# Echo 21cc Trimmer Mods (SRM-210SB, GT-2000, etc)



## Team FAST (Jan 9, 2012)

Howdy,

I've decided to start a thread to detail the various mods and testing I am doing on my Echo 21cc Trimmer. I know its not a chainsaw, but on the SRM-210 SB model I can put a 10" chainsaw bar attachement on and make it a pole saw. So there! 

Basically, I wanted to use this trimmer as a test bed project to prove out my MOTA two stroke engine simulation software in preparation for using it on my much larger, much faster Kawasaki H1 500cc and H2 750cc two-stroke triple motorcycle restrorations. But I do love chainsaws as well. See my other threads  Most of the mods I am making to this trimmer directly apply to the saws, so its worth the effort to document what I am doing.

I will update this thread with pics and data as I have time and make more progress.


For now, some background. I started out with a totally stock, totally reliable, and reasonably well tuned out of the box (I was surprised) Echo trimmer:

Front View:






Back View





Muffler view:





A couple of things right off the bat:
1. It has a fixed jet carb (no real mixture adjustment except Idle speed)
2. It has a very restrictive Catalytic Converter/muffler


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## Team FAST (Jan 9, 2012)

Since the muffler appears to be highly restrictive in stock EPA compliant form, I decided to test it, and eventually MOD it. However, it turns out that the earlier GT-2000 muffler is a direct bolt on replacement. It has no catalytic element inside, so it should flow a lot better. I scored on of these on Ebay, and then I cleaned it up using my Harbor Freight soda blaster (really useful way to clean engine parts!)

SRM 210SB cat muffler on left, GT-2000 muffler on right:





Here's an exploded view of the GT-2000 muffler:





To test the mufflers and get a TRUE comarison of their relative performance in terms of gas flow, I machined an adaptor plate matching the stock exhaust port outlet side and installed them on my SuperFlow SF-110 flow bench

Adaptor:





GT-2000 Muffler installed


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## FlyLow (Jan 9, 2012)

WOW, you're serious. I like it! 

I'm curious to know what the flow differences are.


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## Saw Dr. (Jan 9, 2012)

FYI, many of those carburetors DO have an adjustable needle. There is only one needle and it is pretty well hidden, but you can make small changes. I have had little luck on those. As soon as you change something and adjust the carb, either the high or low end is not correct. If you find a traditional carb to fit then it might be worthwhile. Some of the handheld blowers use a two-needle carb on this engine, but I have never tried to swap one over. This should be a very interesting thread. There are SCADS of those Echos around, and most of the parts are interchangeable. Once you tell everyone what the best combo is, the prices will skyrocket on Ebay.


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## Team FAST (Jan 9, 2012)

*Muffler Flow Data*

Here is the muffler flow data:






It turns out that the earlier GT-2000/SRM-2100 muffler flows 75% more than the cataylic converter muffler. If you eliminate the arrestor screen backing plate, you pick up some additional benefit and it flows nearly twice as much!

If you omit the cover, (basically an open hole where the arrestor screen goes) the flow is up to 2.5x the cat muffler stock.

So this becomes a true bolt-on Muffler Mod!

The other interesting thing is how much heavier the cat muffler is. It weighs more than twice as much. I feel this is significant, especially for a landscape professional who has to heft this tool for hours at a time during the course of a day earning money. Clearly there are performance reasons to do this muffler mod beyond just making more power!


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## Team FAST (Jan 18, 2012)

*Engine stand fab*

I decided that in order to execute all of the modifications I plan to do, I figured it would be better if I had a second motor to play with. Lower risk that way, because if I mess up the modifications, I won't ruin my trimmer (keeps my wife the accountant happier that way). So I scored an earlier Echo GT2000 powerhead on Ebay (for $10!) and it was in great running condition. The best part was it had the earlier Zama/Walbro WT-424 carb with adjustable mixture (this engine had the Zama).

In addition I scored two "freebie" engines from my local mower shop. These were worn out partially disassembled 21cc engines. One was a SRM-2100 and the other was a GT-2000 "Type 1e" model. At the time, I had no idea what that meant, but when I compare the cylinders, I will highlight the differences. 

So now I have a nice collection of bottom ends, ignitions, and cylinders to play around with. The first thing I decided to do was design and fab up a nice little workstand so I can easily work on the engines.

Here's a 3D CAD model of my workstand:







And here's the final product with the Ebay GT-2000 engine mounted:





One more:





I TIG Brazed the steel tubing together and machined a stub shaft on my lathe to fit into the trimmer clutch housing. Makes it really easy to rotate the engine around to work on it.

Next I will talk about the differences between the cylinders.


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## drumbum (Jan 18, 2012)

Kewl


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## c5rulz (Jan 18, 2012)

I'll throw some rep at ya. This look interesting.


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## Team FAST (Jan 18, 2012)

*Cylinder Differences*

It turns out that there are some interesting differences in the transfer port arrangements of the three "donor" cylinders I acquired.

From left to right: 

GT-2000, SRM-2100, and GT-2000 Type 1e






As you can see, there are some big differences between the transfers. There are also differences in the intake port sizes and timing. Below are the intake ports. 

from left to right: GT-2000, SRM-2100, and GT-2000 Type 1e






Does anyone happen to know what the Type 1e designation is supposed to be? To anyone purchasing an Echo trimmer, you would be none the wiser as to any of the differences between these cylinders! The port timing numbers are close.....but the intakes differ quite a bit because of the size (and therefore flow) difference.

All of the cylinders are nikasil plated, and have the exact same external dimensions and bores. They are interchangeable.


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## Team FAST (Jan 18, 2012)

*Instrumentation*

I need to know the RPM range of the trimmer. I've spent a lot of time reading on these forums, and seen all the typical tachs used for chainsaws. The problem is that I need to see engine RPMS during operation of the trimmer. The handheld chainsaw tachs don't work very well for that. I discovered a cool little compact solution. The Trail Tech tach. It's pretty basic, but it does feature a 1/2 second update rate (barely adequate) but it does record max rpm during a run session which is handy. It is also an hour meter. The best part is that it is super compact.

I mounted it on my trimmer in front of the lower handle, within easy eyesight during operation:






There is a wire pickup which has to be wrapped around the ignition wire. The unit has a built in battery.





So Here's what I learned:

Once warmed up, the trimmer idles at 3400 rpm
With the dual line head at max length (17" cutting diameter with .105" line) the max rpm at WOT is 8000
With no line showing at the head, the max rpm is 10,560

(BTW in the picture, the tach is reading 2400rpms....this is the max rpms I could get using the starter rope and pulling the engine through without a plug installed....interesting, huh?)


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## Nardoo (Jan 18, 2012)

Great thread! I have one of those little SRM 2100,s. Well built and snappy.

Al.


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## Miles86 (Jan 19, 2012)

Type 1E is for the "emmissions" model has a carb with limiter caps, the other non "E" has a carb with no limiters,just a regular screwdriver high / low needles.

Note the 4 channel transfers for the emmissions model, to give higher gas velocity in the transfers , better mixing and scavenging for more complete burning.


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## turtle561 (Jan 19, 2012)

great stuff 
worthy little motors for sure.
i see the 'borg' carb on the SRM210SB. those have adj. jets on them too.
opcorn:


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## Team FAST (Jan 19, 2012)

Miles86 said:


> Type 1E is for the "emmissions" model has a carb with limiter caps, the other non "E" has a carb with no limiters,just a regular screwdriver high / low needles.
> 
> Note the 4 channel transfers for the emmissions model, to give higher gas velocity in the transfers , better mixing and scavenging for more complete burning.




Thanks for the clarification on that. That is what I suspected was the case. The interesting thing is that when I modeled all of these transfers using MOTA (details to follow) this Type-1e cylinder produced the best horspower and torque. Especially when I started altering the port timing for more top end performance. The SRM 2100 cylinder in the middle of the picture has very small transfers and therefore doesn't breathe very well in the model/simulation.


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## o8f150 (Jan 19, 2012)

this isn't a chainsaw thread but i like it


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## booger1286 (Jan 19, 2012)

This is great stuff. Icant wait to see it in action when your finished. I have modded a couple of my trimmers too with really good success and love the difference in power. You should find a stihl fs 85 and mod it, they are very solid built with adjustable carbs and steel shafts.


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## Team FAST (Jan 26, 2012)

*Initial MOTA results*

Here is a baseline plot from MOTA showing the power and torque curves. This is the GT-2000 cylinder.







I took great care to accurately measure the engine and capture all the physical attributes about the engine. Port timing, crankcase volume, squish, chamber volume, ignition timing, port shapes, etc. I used a box muffler model for the exhaust. 

I am pretty happy with these results. While it's difficult to find published data on Echo horspower output, I have seen some references which suggest that peak horspower output on their 21cc engines is around 1hp. The power curve also seems to emulate the performance I get from my stock trimmer. (see my post above about tachometer readings). Plus it is a reasonable looking power curve.

One general comment: The exhaust port timing on all these cylinders are really conservative! (low) obviously they are tuning for low end torque.


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## Team FAST (Jan 27, 2012)

*Time for some Mods*

So based on what I learned so far, I made a game plan:

1. the port timing needs to be seriously adjusted. The exhaust ports are too low and the transfers are too restrictive -- Look into porting the cylinder

2. The carb is very small and restrictive -- adapt larger carb?

3. The exhaust (with the higher flowing muffler) may be adequate, but the ideal solution might involve an expansion chamber


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## Team FAST (Jan 27, 2012)

*Carbs*

I have a stash of misc chainsaw, trimmer, and blower carburetors which I have procured on Ebay, from old equipment, etc. I dug through the pile-o-carbs and found a Walbro WT-532 (from a Husky XPT 335 chainsaw). This carb has a simliar body and I can adapt the Echo thottle lever over to it. I machined a new adaptor plate for the flowbench so I can flow carbs, and did a head to head comparison of the WT-424 (Echo GT-2000 carb) to the much larger venturi WT-532. 

I also progressively flowed the airfilter and choke plate on the stock setup to see what the flow restrictions are like with each piece. On the WT-532, I experimented with removing the choke plate and shaft. I'm considering using a velocity stack and getting rid of the Echo air filter assembly in favor of a K&N setup.

I'm thinking if I can get the motor to breath better, and perhaps even use a pipe, the larger carb might be the ticket to a real screamer!

So here's some pics.

Here's the stock GT-2000 carb mounted on the flowbench. I hold the throttle butterfly open to WOT condition during all flow testing.






Here's the choke assembly installed:





And here's the air filter config:





Here's a comparison of both carbs. WT-532 on left, WT-424 on right. I can easily swap the primer bulb assembly over to the over carb. Retrofitting the throttle lever will require a bit of machining.






Finally, the flow data:






I'm liking the fact that the larger carb flows more than TWICE what the stock one does!!! There is plenty of flow capacity to keep up with my other mods.....


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## slipknot (Jan 27, 2012)

*mantis tiller has a echo trimmer engine..i do believe.*

These are basically the same engine platform as the mantis tiller?? I wonder what bigger echo engine i could drop down onto the mantis. I did a mild woods port on one last year but have since scored the piston and cylinder. IMO.....the stock mantis engine is a really too small and under powered. I like this thread..im about to learn a whole bunch..thanks.


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## steve316 (Jan 27, 2012)

just subscribing


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## slipknot (Jan 27, 2012)

I think the mantis engine is 25cc....my bad.


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## slipknot (Jan 29, 2012)

c'mon fellas this thread aint done yet..there's more to know.


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## Miles86 (Jan 30, 2012)

I could see getting the power up to 2.5 to 3.0 hp. The Zenoah G230RC is 22.5 cc and is available from RC shops rated at:

quote from an RC website: 

"Available in factory black finish or with aftermarket chrome shroud, fancover, etc pre-installed. 
Engine Stats: Displacement: 22.5cc. Power: 2.8HP @14,000 RPM. Torque: 1.32 ft/lbs @10,000 RPM. Timing:30 degrees BTDC @ 8,000 RPM. Compression Ratio: 9.2:1. Fuel: 95 octane or higher mixed 25:1 with 2-stroke oil."

How long these Zenoahs' last is ????:msp_unsure:


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## Team FAST (Feb 7, 2012)

I've seen simliar info. I've been looking at what the Zenoah folks have been doing for modifications (RC cars, boats, and also scooters). I've also found some people who are modifying these echo string trimmer engines for use on R/C aircraft.

My plan to get more power is to raise the exhaust port for more rpm, open up the transfers, and try and get a decent combustion chamber setup (squish and volume). And install a bigger carb for better breathing. Something else I am cosidering is building a pipe. Howe cool would THAT be? 

The holy grail would be a programmable ignition with a non-linear advance curve. The fixed timing on these engines really holds them back.


I've got some more stuff to post, just need to find the time....




Miles86 said:


> I could see getting the power up to 2.5 to 3.0 hp. The Zenoah G230RC is 22.5 cc and is available from RC shops rated at:
> 
> quote from an RC website:
> 
> ...


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## Miles86 (Feb 7, 2012)

Team:

Like the module on the CS-370? They state it is a slope advancing unit, not sure how that works, does it retard for starting then variable advance through the rpm range? Or just wham-full advance at x rpm? My cs-370 is just a little rev machine, very happy with that saw.

I need to order some of those 21 cc muffler outlets for my other echos.


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## Team FAST (Feb 8, 2012)

Interesting idea!

I will have to look into the CD-370 ignition module. Never thought of that! I have a pair of CS-400 saws, so I wonder if they have a similar module. I will have to hook up a degree wheel and a timing light and see if there is a timing curve built into that module.

If it works, I may be in the hunt for a CS-370 ignition module....


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## PLMCRZY (Feb 8, 2012)

Just curious are you retired?


Sent from my iPhone using Tapatalk


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## Team FAST (Feb 10, 2012)

PLMCRZY said:


> Just curious are you retired?
> 
> 
> Sent from my iPhone using Tapatalk




Not even close! Why?


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## PLMCRZY (Feb 10, 2012)

Team FAST said:


> Not even close! Why?



How the hell do you have time for this stuff lol? I think it's cool for sure but you put a lot of time into your stuff it seems. 


Sent from my iPhone using Tapatalk


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## Team FAST (Feb 10, 2012)

I decided to get a bit radical. I think the biggest limitation to getting decent port timing and squish settings in trimmer and chainsaw style engines is the fact that these are one piece cylinders with the cylinder head cast into the top. If you start raising up the cylinder to get better exhaust port timing, you increase the squish...not a good thing.

So I decided to get radical and try something I haven't seen done a lot on here on this board. 

First I machined a mandrel from 6061 bar stock so I could conduct machining operations to the cylinder in my lathe:







Here's a pic with it installed in the cylinder. It's slip fit into the bore.





Then, I took the GT-2000 cylinder and cut the top off using my bandsaw:






Next, I mounted the cylinder onto the mandrel and then installed it into my lathe using a 5C collet chuck. I designed the mandrel so that the stock bolt holes could be used to support and attached the cylinder to the base flange. I machined the actual mandrel to be a close tolerance slip fit to the stock bore. Here's how it looked with the cylinder installed (before I cut off the top)






OK. So once I cut off the top, I used the mandrel in my lathe to machine the top of the cylinder smooth and square. At this point, I don't know how much to take off, so I machine it to only clean up the top of the cylinder. Later, when I go to set the port timing, and eventually the squish clearance, I will take more off as needed.






And here is the finished product from this operation:






Now this is starting to look like a real cylinder! Something that I can work with to accomplish good porting, tuning and lots of horsepower!


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## Team FAST (Feb 12, 2012)

Here's what going to be installed on top of the now open cylinder:






This head has a nominal 3cc volume (total volume above the piston) with a 15 deg squishband. Best part is that it is a hemi chamber with a centered open spark plug. The stock head has an asymetric chamber with a very shrouded spark plug. 

Making the leap from "virtual" CAD to "actual" metal here is the starting point. I sawed the billet from .625" 6061 plate





Machining the edges:





Finished the mounting holes. Notice there are four holes. The Echo cylinder is attached to the crankcases be only two bolts. More on that detail later 





Now with a M14x1.25 spark plug hole:





Machining the cooling fins. Takes MANY passes with a .125 diameter ball nose carbide endmill! All the edges were also machined with radius cutters (corner rounding endmills)


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## Team FAST (Feb 12, 2012)

*Finished cylinder head*

And here is the finished product:











Here's what the combustion chamber looks like. This is actually a prototype head I made. On the first attempt, I messed up on the dimensions of the mounting holes, but I went ahead and finished it. I also had a problem with the spark plug threads, so I installed a thread insert. Otherwise, this is identical to the second part I made. So you are looking at my "Revision A" of my cylinder head design 






I still have to machine a counterbore on the sparkplug hole to properly set the depth of the plug. I am going to wait to do this until I get the squish set properly and the cylinder ported.


Next, I will show how I modified the crankcases to the entire assembly will fit together.


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## dboyd351 (Feb 12, 2012)

That's awesome!!! I agree the one piece cylinder head is a real limiting factor. Love to see you machining up your own solution. This is going to be an amazing thread to follow. I also like the other extreme, with the bolt on muffler mod. A little bit of something for everyone!


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## Team FAST (Feb 12, 2012)

Thanks! I think when I am done I hope it's going to be a piped snarling fire breathing monster. I haven't ruled out running alky and nitro to get the most power.....


Yeah I know, its a weed eater....:tongue2:


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## Team FAST (Feb 12, 2012)

Design time again. I needed to make another fixture. This time I got two for one. This fixture allows me to mount each crankcase half against a reference surface. Turns out that the good folks at Echo designed their cankcases to allow provisions for two additional cylinder attach locations. The bosses are cast into the crankcases, but they aren't drilled or tapped. So after much measuring and layout, I reverse engineered the bolt pattern for the cylinder base, and established the locations for the additional holes. The new head needs four strong attach locations to clamp everything together to seal it. 

The second thing this fixture does is provide an accurate way to bolt up the cylinder so I can drill the extra holes for the attach bolts through the fins.

Also turns out I can mount the cylinder on this plate sideways and directly machine the exhaust port in the mill. Haven't done that operation yet, so stay tuned....

Here's the CAD layout:






Here's a set of cases set up on the mill with the new holes drilled and tapped:











Here's what the cylinder looks like installed (sort of). I made up some studs, which are shown here, but later I decided to purchase M5x65mm socket head cap screws.






Also, having the cylinder open on top makes it a CINCH to measure and set port timing (as it should be).


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## cujet (Feb 12, 2012)

I'd love to know what port timing specs were stock and what you end up with. Also, your predicted HP. 

Obviously, a well tuned pipe would be best, but there are compact alternatives that may produce more power than a modified stock muffler. 

I had considered trying a larger volume muffler, with internal standpipe to reduce noise levels.


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## Team FAST (Feb 12, 2012)

Let's see....port timing for the Type Ie cylinder (which is what I am going to use to modify) stock is:

Inlets open at 65 deg BTDC with 130 deg duration
Transfers open at 48 BBDC with 99 deg duration
Exhaust opens at 115 ATDC with 135 deg duration

The exhaust port timing is super low. I'm going to raise the exhaust significantly. That's why I had to cut the top off the cylinder and machine my own cylinder head.


I haven't had time to do any porting yet, so I welcome any inputs for where to put the ports.


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## cujet (Feb 13, 2012)

Can I suggest 196 degrees exhaust port timing and 135 degree transfer port duration. You have no "guts" if you don't go this radical, ha ha. Of course, that would require a properly tuned chamber and case reed induction. What fun. 

I am totally impressed with your modification plan. Very cool indeed.


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## Miles86 (Feb 13, 2012)

TeamFast;

Great job as usual! 

How are you going to stop the head from warping? Maybe use the stud method with a spacer collar to act as a limit stop? (The cylinder fins are not uniform in their shape at the top of the cylinder, maybe it doesn't matter.) Thanks again for sharing.


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## Team FAST (Feb 13, 2012)

*Warping*

I hope warping won't be an issue, as the thickness of the head below the fins is almost .250". So that's a 2.5" x 2.5" x.25" thick plate being bolted on top of the cylinder. The bolt circle is just outside the cylinder section, so there isn't a lot of cantilever to distort things when I clamp it together with the bolts. I expect cooling to be adequate because the total cooling fin surface area is more than the stock fins I removed.

I still have to work out sealing the head to the cylinder, but my plan is to machine an o-ring groove in the head, and then make an O-ring from copper wire with some "crush" designed into the dimensions. If I get it right, the two aluminum surfaces should seat together with the copper O-ring providing the sealing.


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## promac850 (Feb 13, 2012)

Geez, and I thought I did a good job with my Ryobi SS30...

You're raising the bar!


Dammit, now I need to get a Bridgeport... bad. Blasted college, if I didn't go, I could've bought a BP...


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## Team FAST (Feb 13, 2012)

Thanks!

Your Ryobi String Trimmer mods thread was actually an inspiration for me to move out on my project. So I can now tell my wife its all your fault 

I have a Ryobi trimmer that a co-worker gave me in good (running) shape. I think it may be the same model as yours. I will check tonight. 

The thing I like about the Echo trimmers is the bottom end is really solid. Two main bearing crank with forged conecting rod = lots of high rpm goodness. I wish the crank was full circle like a proper two stroke race crank. I suppose I could machine my own, but the dynamic balancing would be tricky.


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## dboyd351 (Feb 13, 2012)

Miles86 said:


> TeamFast;
> 
> Great job as usual!
> 
> How are you going to stop the head from warping? Maybe use the stud method with a spacer collar to act as a limit stop? (The cylinder fins are not uniform in their shape at the top of the cylinder, maybe it doesn't matter.) Thanks again for sharing.



Pretty much all 2 stroke dirt bikes are built this way and all they use is a head gasket.


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## Team FAST (Feb 13, 2012)

*Cylinder head test fit*

Here is the cylinder head installed:







This side shows one of the new fasteners added by me.





Here's the cool part. The new head fits under the stock plastic cover!





Another view:





One last pic:


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## dboyd351 (Feb 13, 2012)

Sweeet!!!


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## steve316 (Feb 14, 2012)

*great mod*

I have never had any desire to cut the head off a blind clinder before, but after this post I am all fore it. I am looking at some new toys and as soon as I have them I am going for it .GREAT POST. Steve


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## Chris-PA (Feb 14, 2012)

You are nuts, and I'm lovin' it! Nice work!


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## Team FAST (Feb 15, 2012)

*Porting Question*

I have a question. I am considering eliminating the divider between the two small transfers on the Type Ie cylinder to make them larger single transfers. Does anyone see any problem with this? 

Based on what I've seen from my MOTA computer models, and also my experiences with kart engines, bigger transfers are rarely a bad thing.

Thoughts?


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## HiOctane (Feb 15, 2012)

Still enough rings support to avoid catching ?


Team FAST said:


> I have a question. I am considering eliminating the divider between the two small transfers on the Type Ie cylinder to make them larger single transfers. Does anyone see any problem with this?
> 
> Based on what I've seen from my MOTA computer models, and also my experiences with kart engines, bigger transfers are rarely a bad thing.
> 
> Thoughts?


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## Team FAST (Feb 15, 2012)

I think so. There are single ring and double ring pistons available from Echo. I Don't know what drives them to use one vs. the other. There are performance gains to be had from a single ring piston, but probably longevity benefits from a dual ring piston...seals better and holds compression longer over operating hours. 

What is the rule of thumb for the amount of ring support needed across a port window so as to avoid hanging up a ring on the edge of a port?


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## HiOctane (Feb 15, 2012)

I know that an ex port should not be larger than around 65 % of bore to avoid problem,should the same % for tranfer i guess.



Team FAST said:


> I think so. There are single ring and double ring pistons available from Echo. I Don't know what drives them to use one vs. the other. There are performance gains to be had from a single ring piston, but probably longevity benefits from a dual ring piston...seals better and holds compression longer over operating hours.
> 
> What is the rule of thumb for the amount of ring support needed across a port window so as to avoid hanging up a ring on the edge of a port?


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## Team FAST (Feb 15, 2012)

I'll check it out. It's also going to depend on where the ring end gaps fall.

I need to acquire some porting tools, small carbide stones, etc. to get the cylinder porting done.

Here's a pic to clarify what I am talking about. I want to possibly get rid of the ribs (or divider walls) that I circled.


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## steve316 (Feb 17, 2012)

*to rib or not to rib*

you can remove the ribs below th rings travel and still have the suport. if you are wanting more transfer port area take the the port closes to the intake towards the intake the thickness of the divider.I have made this mistake in a dirt bike years ago, just my blunder but it may work for you.great post Steve


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## cujet (Feb 19, 2012)

Any more updates?

I'd love to know what your predicted HP is. I'm sure the software will give you a value. 

Are you trying to go with practical power or is this an "all out" exercise in power production?


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## Team FAST (Feb 24, 2012)

cujet said:


> Any more updates?
> 
> I'd love to know what your predicted HP is. I'm sure the software will give you a value.
> 
> Are you trying to go with practical power or is this an "all out" exercise in power production?




I will post some updates this weekend showing some predicited gains in horsepower due to porting, carb, etc.


I started out thinking this would be a "practical power" mod, however when I started acquiring all the spare parts, I rationalized that I could build an all out fire breathing effort. After all, that's what its all about right? MORE POWER. But as I document my progress along the way, you can determine which levels of "mod" is right for your application. 

As a result of the feedback I have been getting from this thread (including several non-members who visited the site) I am considering a couple of new ideas for this project which would really make it stand out. One thing I am contemplating is building a dyno to test the engine for real. I could also then test other folks saw engines.


I'm also tempted to have a go at the Poulan "Wild Thing" build off.


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## dboyd351 (Feb 24, 2012)

Team FAST said:


> I will post some updates this weekend showing some predicited gains in horsepower due to porting, carb, etc.
> 
> 
> I started out thinking this would be a "practical power" mod, however when I started acquiring all the spare parts, I rationalized that I could build an all out fire breathing effort. After all, that's what its all about right? MORE POWER. But as I document my progress along the way, you can determine which levels of "mod" is right for your application.
> ...



I'm looking forward to it. I think the Wild Thing build would be great, too. Nothing like a cheap, universally available saw to experiment on.


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## k5alive (Feb 24, 2012)

:msp_drool:


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## steve316 (Feb 24, 2012)

*dyno*

I am wanting to build a dyno myself.I am looking forward to you thoughs on design for one. GREAT POST.Steve


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## Team FAST (Mar 11, 2012)

Some things arrived at my shop in the past two weeks:

A Ford 3G alternator:






And a Hubbell Resistor Load bank with enough capacity to absorb power from probably half my house:






I have no idea, but they might be really handy for someone who wants
to build an eddy current dynomometer. I don't know. Maybe? 

I already had several load cells, and a variable voltage DC
power supply handy as well.

Alternator has already been cleaned, torn down, rebuilt, modified.


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## Hulsty (Apr 27, 2012)

updates?


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## gcdible1 (Apr 27, 2012)

FlyLow said:


> WOW, you're serious. I like it!
> 
> I'm curious to know what the flow differences are.



Thats what I was thinking...all scientific and shi:msp_wink:.

I had both the gt200i and the gt2000. Both ran great for me for several years.:msp_smile:


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## osut362 (May 6, 2012)

bump


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## Team FAST (Mar 23, 2013)

I have some updates....but its been a while. Been busy with work, etc. Will try and post them soon.


Anyone know why my pics are no longer showing up? I hosted them on my picasa account.


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## steve316 (Mar 24, 2013)

*pictures*

Don't know why they are not showing up but would like the them. Steve


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## Chris-PA (Mar 24, 2013)

Team FAST said:


> I have some updates....but its been a while. Been busy with work, etc. Will try and post them soon.
> 
> 
> Anyone know why my pics are no longer showing up? I hosted them on my picasa account.


Why don't you just upload them to AS directly instead of using a 3rd party site? With a 3rd party site link, if they change the URL even slightly then the old link is no longer valid and they're gone.


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## LegDeLimber (Mar 24, 2013)

Has anyone run into these screws?
Theses came from an Echo pb-500 blower.
screw holes are indicated in second pic.
They were recessed into the body, in about 1/8" diam hole.
They take a small size "D" tool, the head is about 2mm.
Thought I found a tool for them but it was $50 before s&h
(area dealer wouldn't even discus it or those screws [..can't say that I blame them though])

The walbro ipl lists two different screws in this carb WLA-1-1
high & low, but neither one is like these and don't appear to be a fit.
( funny that the walbro page doesn't even display an image )
Found a site that had the correct part displayed, 
but at $14 a piece !! (plus shipping)

hmm, was time to take a power tool to the carb.
couldn't turn them with a slot (tried 3 times) 
and finally had to just dig down to get pliers on them
that nylock insert made 'em damn hard to turn.

these are why I wondered what pitch Stumpy used on his carb build. 
http://www.arboristsite.com/chainsaw/232204.htm


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## Chris-PA (Jul 30, 2017)

I was thinking about this thread this weekend while I worked on my 25 year old SRM-2410. The shaft broke on it last year, and I have been meaning to get another but had not bothered yet - then my neighbor threw out an SRM-2400, with a good shaft! They were both filthy and naturally I had to clean them up, and of course soon they were both pulled down completely. Mine was SN 20,xxx or thereabouts, and his was SN 161,4xx or so, and there were several major differences. My older engine was 1-ring, and had larger transfers (both are dual transfers) with a larger opening volume at the bottom. It also had some light scoring stripes, although it was usable. The amount of carbon in it, and blocking the exhaust port, was amazing. I must have run some real crap oil along the way.

The newer engine has 2-rings and lower volume, higher velocity transfers with a pocket-shaped profile to give better outlet angle and loop scavenging - it looked a lot like the jug in post #53 in this thread. The bore was in near perfect shape, so I wanted to use it, but sadly it had a significantly narrower exhaust port. Timing seemed about the same. The new engine had a very small Walbro carb (with a 20/64" venturi), while the ZAMA on my old trimmer was about 28/64" - pretty big for a 23cc engine!

So, I decided to open up the exhaust to about 56% of the bore (my old cylinder was only 50%), and used the newer jug. I figured the newer design lower transfers would help reduce case volume too. I removed the base gasket (only 0.010"), and drilled the 6 holes in the exhaust baffle from 0.235" to 0.250" (a 13% increase in area). I also used the bigger carb. All the carbon got removed from the piston, cylinder and rings, and I put it back together with all the best covers and parts from the two. 

I can't believe how the thing runs! It's amazing what just a couple of tiny mods and the right parts can do. I've been using my ported PP338PT, and that has just a little more power, but it's heavy, poorly balanced and I hate the trimmer head (feeds string all the time). Clearly the old Echo was down on power at the end, but I don't think it ever ran like this. It's got the power now to keep the rpm up through heavier, thicker stuff so the line won't get caught. Now the Poulan can go back to pole saw duty.


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## James Miller (Jul 31, 2017)

Iv never modded one of the echo motors but iv done a few older homelite bandit trimmer motors for friction bikes. I have one on the bench right now with BG delete and stuffed crank case Gona see how it runs and then maybe widen the ports. Never done any porting before so could be interesting.


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## GeorgiaVol (Jul 31, 2017)

Thanks a lot. I was perfectly happy just working on my saws, now you got me thinking about the SRM225 over in the corner and the 2 extra powerheads I have. Now look what you did!


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## Team FAST (Jul 31, 2017)

Looks like I need to re-post a whole lot of pictures. Here's where I left the project a couple of years ago...billet machined separate head on an Echo cylinder. Cases modified with four bolts attaching the cylinder/head assembly.




The cylinder after I cut off the original Echo cylinder head and machined it. The head will have an o-ring groove for sealing.





The cylinder head I machined.


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## Team FAST (Jul 31, 2017)

Here's PHASE 1 which is the way I run the trimmer today.

Phase 1:
- Removed stock non-adjustable barrel carb
- installed blueprinted Zama adjustable carb from Echo GT-2100 trimmer...not straightforward....had to modify the throttle cable. The butterfly screw has been replaced with a low profile button head screw (better flow)
- removed stock choke assembly and replaced with aftermarket Go-ped style choke and velocity stack/K&N style air filter
- replaced stock CAT muffler with older style box muffler, ported.
- installed Trailtech tachometer

I've been using it like this for two years now. It runs STRONG, and is just as reliable. I loaned it to my neighbor a couple of weeks ago and he couldn't believe the difference in power/performance as compared to this Husky String Trimmer (which I have also worked on for him....see my Husky trimmer thread).


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## Doskiez (May 30, 2019)

Ok I know this is resurrecting an old thread but this thread was my inspiration, and what I found out might be useful to those who have this trimmer. I was given an echo ES210 blower that was straight gassed and as I was ordering parts and looking at it it got me thinking about my trimmer SRM210 which shares basically the same running gear. I was hoping to get a little more power out of it so I decided to tear into it too. The main restrictions to these seem to be the carb, muffler, and base gasket transfer holes (Thanks EPA) to correct this I did the following.

Doubled the size of the outlet slot in the muffler,
Opened the exhaust port up about 2thou on each side and raised the top 1 thou (while removing what looked like a casting defect bump and channel on the top of the port.
Cut the restrictor holes on the base gasket for the transfers (opened them up to the profile of the tranfer rather than being 3 little holes.
Smoothed/ rounded the blunt edge of the seperation between the two transfers (cylinder brace) 
And finally but in no way least fitted a carb for an SRM 260 trimmer. the 260 carb is a direct bolt on, you can still use the factory filter housing (although I am going to try out the 260 housing for the larger filter) and it moves you from a 9mm venturi on the stock carb to a 12.2 mm 
Testing the trimmer with all mods listed above and stock carb still showed improvement over stock (high speed jet was maxed out) but the addition of a larger carb made a huge difference. Revs much faster, holds RPM better through aggressive cuts and there is still adjustment left in the high speed jet to support further tweaking if wanted.
From this experience I think simply opening the base gasket transfers, opening the muffler up some, and the larger carb would still net good results on an otherwise stock trimmer.
Anyway thanks for the inspiration, I hope this helps some of you without access to a flow bench and machine shop, and I couldn't be happier with how this fairly simple mod turned out.


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## James Miller (May 30, 2019)

I noticed a decent gain just splitting the muffler and pulling the cat plate out of my srm 225.


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## Victor A Van Natter (Jun 23, 2019)

I also saw an impressive gain just cutting out the deflector plate in the muffler on an arm 225. Only problem now is it runs a bit rich. Used about 30% more gas than usual. But power definitely improved


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## John Walsh (Jun 7, 2020)

What an interesting thread! Thanks for the science, and the mechanical artistry involved here. I'll bet it influences a lot of people to make mods to their 2-stroke equipment from mild to wild.


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## John Walsh (Jun 20, 2020)

Team FAST said:


> Howdy,
> 
> I've decided to start a thread to detail the various mods and testing I am doing on my Echo 21cc Trimmer. I know its not a chainsaw, but on the SRM-210 SB model I can put a 10" chainsaw bar attachement on and make it a pole saw. So there!
> 
> ...


Those Kawi triples were a hoot. My modded RD400F Yammie is a mini-hoot with expansion chamber exhaust, bored carbs and modded porting


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## mexicanyella (Jun 21, 2020)

Mini-hoot! New vocabulary word!

This has been a fun read; thanks!


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## John Walsh (Jun 21, 2020)

mexicanyella said:


> Mini-hoot! New vocabulary word!
> 
> I used to have a GT380 triple, which was not as “sporting” as the Kawasakis or Yamahas. A quick ride on a buddy’s RD350 (with surprise wheelie) prompted me to try building a set of expansion chambers.
> 
> ...


I'm there with you, 100%, Nothing like the smell of racing castor oil. When I was 12y/o a neighbor had me race a quarter midget for him. I did well in the stock class and the following year he turned the stock car over to a friend's daughter and built an alcohol-burning, castor in the crankcase, highly modified QM for me that was pretty much always in a power slide around the blacktop oval track. That thing BARKED! I remember the GT380 as well. Nice bike! Ah, memories


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## Okie294life (Jun 21, 2020)

Saw Dr. said:


> FYI, many of those carburetors DO have an adjustable needle. There is only one needle and it is pretty well hidden, but you can make small changes. I have had little luck on those. As soon as you change something and adjust the carb, either the high or low end is not correct. If you find a traditional carb to fit then it might be worthwhile. Some of the handheld blowers use a two-needle carb on this engine, but I have never tried to swap one over. This should be a very interesting thread. There are SCADS of those Echos around, and most of the parts are interchangeable. Once you tell everyone what the best combo is, the prices will skyrocket on Ebay.


I bet there is no jet adjustment. A lot of these trimmers are using the new awesome rotary valve carb by Zama and they don’t have any adjustments, just throw away and replace. If you’re running more flow that could be a problem. If you’re serious about hp, you should look at a different head unit, or yank the engine off a larger trimmer.


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## mexicanyella (Jun 21, 2020)

I had some success on a muffler-modded 31cc Poulan Pro with a one-needle Walbro carb...It seemed pretty rich in the upper midrange and up top when the low-speed mixture was right, prior to the muffler mod. After the muffler mod leaned it out a bit (just drilled a few 9/64” holes aimed rearward to exit without melting the plastic shroud), it was better but still a touch rich. Running 32:1 got it about where it needed to be. Kind of the long way around the barn, but it was a dumpster-dive special and it has held up pretty well. It’s the backup to my backup now...kinda loud but reliable for four-five mowing seasons at this point. 

Those upside-down Ryan/IDC/Ryobi/Poulan/Troy-Bilt engines, coming soon to a dumpster near you, are pretty crude but they seem to have pretty decent midrange torque...pretty handy for careful trimming around chain link fence or plants you care about. I’ve had several over the years and never had a problem with the cantilever crank or bearings. It’s always trimmer head or recoil problems, seems like, and the occasional carb
Kit. I seem to remember reading that the large-scale RC guys using them tried to keep them below 7500 rpm with prop size and pitch...so not in the same league of bottom-end robustness as modern pro grade trimmers, or even cantilever-crank 25cc Homelites. 

Okay, digression over; carry on.


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## Chris-PA (Jun 22, 2020)

My newer Echo 21cc trimmer has a ZAMA RB. The screw is called out as a main mixture screw in the diagrams. It does seem to do something, but it's not very sensitive. Next time I have it apart I'm going to try to figure out how the fuel circuit works and how that needle functions.

My stock 21cc with the RB carb does not have near as much power as the ported 24cc with a conventional carb, but it's not all that much less and it uses significantly less fuel. Also, with a cat muffler it stinks a lot less.


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