025 muffler mod

[nelly]

What kind of gains could you get out of a consumer saw? Is this something that would help with power and coolness etc.

Just what would I do to open it up. What size holes If I am drilling the baffel and how much on the front plate. Do I have to worry about carb adjustment afterward.

I have taken the muffler off and it comes apart. It would be very easy to work on.

 

[spreaderman]

how I did mine

I have a 023 and I drilled out the bottom of the basket that is in the muffler if there is one , and there is three holes in the muffler that have a angle half covering them ... or mine did ..... I drilled all of them out and added 1 more hole under them ... I used a bout a 5/16 bit ... maybe a little larger .... just try to match the size allready there ...... it will add a little more thump to the sound but you will also like the quicker tach and power .... I hope this helped

 

[rbtree]

nelly,

If there are any innards inside the muffler, lose em, or at least drill em way out. make the port openings 1.25- 1.5 times as large as the cyl. exhaust port.

power gains will be good, consumer or pro saw...15-20% perhaps.

 

[Greg]

Wouldn't the saw then require some carb adjustment to run right?

Would you say that opening the mufler is a good thing for all 2cycles? (saws, blowers, etc..)

How important is a spark arestor screen? is it more to keep dust out than containing sparks?

Greg

 

[treeclimber165]

Greg-
Carb adjustments, if any, are extremely minor. It depends on just how restrictive the muffler is and how much you improve the airflow. More airflow will increase the percentage of air to fuel, so fuel will need to be increased slightly to match the airflow (richen it up a tad cause mods will lean it out a little).

Muffler mods are practically necessary for any current 2-cycle engine. Manufacturers have been forced to reduce emissions and have had to reduce horsepower in order to meet EPA requirements.

I used to throw my spark screens away. Now I don't, mostly because of what I have learned here. 2-cycle engines can (and do) create a vacuum in the muffler between cycles. Without a screen, sand can be sucked back into the cylinder when making a stump cut, for instance. I never replaced the screen in my climbing saw, but I no longer will use it for a small stump cut either.

 

[nelly]

Originally posted by rbtree
nelly,

If there are any innards inside the muffler, lose em, or at least drill em way out.

rb,
The muffler does come apart. Had the innards in my hand. Removing it sounds great but it also is the support post so the front of the muffler does not cave in when tightneing the screws. I could try to find some rods to replace them.

Great point that treeclimber made about the arrestor screen. Whatever I do I will have to leave something to keep the screen in place.

Spreaderman, thanks for the info on what you did. I think I will remove some of the cover angles also. Although that cover just comes off of mine and leaves a big hole. The cover also keeps the screen in place. could remove the whole thing and leave at least a 1" by 1" hole. Would that be too much?

You have given some stregenth to a mechanically declined person.

 

[treeclimber165]

Just cut or drill it out a little at a time. You can always drill a hole larger, real hard to close it back up (unless you are a good welder). The deflector can remain intact. The outlet hole that the screen is mounted against is one of the culprets in the newer saws. My 026 only had a 3/8" hole covered by screen, I opened it up to 3/4" X 1".
The inside baffle can be drilled out also, so it doesn't block the exhaust from leaving the cylinder. Remove the entire muffler from the saw first so you don't get metal shavings in the cylinder.

When you are ready, you can print this thread to keep it by your workbench for reference.

 

[treeclimber165]

OK, I just pulled my 025 muffler to look and see what I did to it and refresh my memory.

The interior baffle that slides down over the two bolts- At the front end of it there will be 2 indents about 1/4" or so to let excess exhaust out. All the rest of the exhaust must pass through the multiple small holes. I took this piece and made the indents about 3/4", or just past the first set of holes. I did this easliy on my bench grinder. Then file smooth all the edges where the grinder rolls up the metal.

The front cover with 3 vent slots- I just took a wide screwdriver and shoved it in each slot and pryed them wider.

Front half of muffler- The rectangular hole behind the vent slots is fine. Leave it alone.

After doing this, my old POS 025 revs up great! Throttle response is instant and the saw is much torquier. Make sure to check your carb adjustment and make sure it isn't too lean. Plenty of other threads here on adjusting carbs, so I won't address that here.

 

[rahtreelimbs]

??????????

I took the muffler off of my Shindaiwa 488 and totally gutted it. I then welded a plate on the front with a 1/2" hole ( may not be big enough ). I didn't want to go too big on the hole size. Anyway the saw was totally ballless. I bought a stock replacement muffler and put it on, now the saw has all the guts it had origionally. Go figure. for now I'm disgusted with it but I'm sure I will be back at it. Rich.

 

[treeclimber165]

Thanks, Rich. But I was giving specific methods and results with a STIHL 025, not a shindaiwa.

Here's the link for instructions on carb adjustments. Much better written than I could say.
http://www.madsens1.com/sawtune.htm

 

[nelly]

treeclimber,
Thanks for your reply. I believe that I will try something very similar. I checked the output hole on the front cover. It was smaller than I originally thought. 7/8 by 5/8. There is room to make this a little bigger while still keeping the original spark arrestor. I will also open up the fins on the top plate to match.

With the innards, I took it apart and saw what you meant. That is something that I could easily do. Out of town this weekend but I'll try it early in the week. I still need to learn about the carb adjustment. I'll do a search here for previous posts.

Thanks,
Greg

 

[nelly]

oops, I also meant to say thanks for the link.

 

[treeclimber165]

I know this is an old thread, but I finally finished my roll of film and wanted to post the pic of my 025 muffler.
I just put a new piston and rings in this 15+ year old saw last month and it runs better than my 026. Super little lightweight limbing saw.

 

[spreaderman]

good job

I did a very similar job on my 023, With the smaller chain than the 026 it does cut close to it.....