Porting a chainsaw muffler

[AH64ID]

Rogan's chainsaw thread reminded me that I have been wanting some info on this for a while. I read that adding additional exhaust ports to the muffler on a chainsaw will really improve the power, that and a larger carb or just a fully adjustable one. I have an MS260 with a 16" bar. It's a great saw, but like Michael, I spend most of my time cutting at altitude. I don't cut too much, but enough that I want a little more power at altitude. I am thinking of porting the muffler, and getting a fully adjustable carb for it. Thoughts? Experiences?

[Rogan]

Ive read a bunch, and watched a ton of videos on this.. Apparently, a little is a lot, when it comes to porting the muffler.. I plan on doing this, once I get a tach for tuning the carb.It seems pretty straight-forward.If you haven't already, John, peruse the Arborsite forum. Tons of info there on it.

[AH64ID]

I found that forum the other night on my tablet, and plan to go back to it and do some more reading. It looks like a lot of great info.

[hd99fxr3]

Rogan's chainsaw thread reminded me that I have been wanting some info on this for a while. I read that adding additional exhaust ports to the muffler on a chainsaw will really improve the power, that and a larger carb or just a fully adjustable one. I have an MS260 with a 16" bar. It's a great saw, but like Michael, I spend most of my time cutting at altitude. I don't cut too much, but enough that I want a little more power at altitude. I am thinking of porting the muffler, and getting a fully adjustable carb for it. Thoughts? Experiences?

On a 2 stroke cycle engine a tuned muffler is more important than almost anything else you can do. Opening up the muffler willy nilly will cause problems. You also need to keep in mind that the carb changes need to be done prior to muff mods and then checked during the runs with muffler mods. The carb can be made to go rich or lean when messing with the muffler flow. For the exhaust you want to tune for the 5-6 impulse wave IIRC. If you don't have a sensor to sample the exhaust during adjusting of the carb and exhaust, to see if your rich or lean you'll just be barking up a storm and not making any progress, and likely ruin a good running saw. Google tuned exhaust pipe. You should pull up enough informtion to get really confused, before you see the light. Confused yet?

[jlwelding]

I did something along those lines years back. I ported and polished the cylinders on a 350 2 stroke yamaha, the motor ran like a bat out - but fowled right spark plug every 65 miles on the dot. If you ran it like you stole it you could get 70 miles before it fowled the plug. I have no clue what I did wrong on the right cylinder.

[hd99fxr3]

I did something along those lines years back. I ported and polished the cylinders on a 350 2 stroke yamaha, the motor ran like a bat out - but fowled right spark plug every 65 miles on the dot. If you ran it like you stole it you could get 70 miles before it fowled the plug. I have no clue what I did wrong on the right cylinder.

Likely your port job on the left cylinder, created more flow than the right side. Hence when tuning the carb you had to richen the carb adj. to get the good flowing cylinder to get to run right, and were way rich on the not so good flowing cylinder (assuming one carb 2 cyl.).