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

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

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

WOW, you're serious. I like it!

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

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.

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!

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.

Kewl

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

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.

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?)

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

Al.

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.

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

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.

Click to expand...

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.

this isn't a chainsaw thread but i like it

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.

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.

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

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.....

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.