Chris-PA
Where the Wild Things Are
I've long been critical of catalytic converter mufflers on chainsaws. This was because they are complete Band-Aids that do nothing to reduce wasted fuel, they just burn it up in a can afterwards, plus they are restrictive and get hot. To that end I took the cat muffler off my Husky 142e 9 years ago, and have been happy with how it's run ever since. It's otherwise totally stock, one of the few saw I have that has never had the engine opened. This is how it looked when the muffler was new:
However, I've long known that breathing 2-stroke exhaust causes me to hack and cough, thanks to all the unburned mix in the exhaust. I have two Echo string trimmers, one ported and modified 24cc, and one stone stock 21cc with a cat muffler. I end up using the stock one with the cat because it doesn't bother me, and it works just fine. About 2 years ago I was having a discussion with @scottr about Poulan's cat mufflers. We did some modifications and I opened one up, and it turns out the cat material is not restrictive, rather it's just a mesh like Poulan usually uses as a spark screen. There's lots of surface area, but the outlets are tiny. I think they are using these like the "Thermal Reactors" that some auto companies tried in the early days of emissions equipment. It's a mostly closed can with a tiny outlet, and a hot catalyst inside to keep it cooking - that way as much of the unburned fuel can get cooked off as possible.
Still, if I mod it like a normal muffler it will flow fine, and the cat material will at least clean up some of the unburned junk. So that's what I did. Here's the 142 with the cat back on - I forgot to get a shot of the outlet, but it's plenty large:
Then I pulled apart a cat muffler from a 42cc. I added a larger outlet to the tiny port that was there:
I see no reason this won't flow fine. So this muffler got put on my most heavily modified Poulan:
Now I expect the extra heat from the cats will cause me more vapor lock issues, especially on the 142 with the Turbo Clean scoop. On the 42cc saw I use this modified cover to reduce vapor lock, and it works quite well:
I ran a tank through both saws cutting hickory today, and they ran just as they always have. They didn't stink so much though.
However, I've long known that breathing 2-stroke exhaust causes me to hack and cough, thanks to all the unburned mix in the exhaust. I have two Echo string trimmers, one ported and modified 24cc, and one stone stock 21cc with a cat muffler. I end up using the stock one with the cat because it doesn't bother me, and it works just fine. About 2 years ago I was having a discussion with @scottr about Poulan's cat mufflers. We did some modifications and I opened one up, and it turns out the cat material is not restrictive, rather it's just a mesh like Poulan usually uses as a spark screen. There's lots of surface area, but the outlets are tiny. I think they are using these like the "Thermal Reactors" that some auto companies tried in the early days of emissions equipment. It's a mostly closed can with a tiny outlet, and a hot catalyst inside to keep it cooking - that way as much of the unburned fuel can get cooked off as possible.
Still, if I mod it like a normal muffler it will flow fine, and the cat material will at least clean up some of the unburned junk. So that's what I did. Here's the 142 with the cat back on - I forgot to get a shot of the outlet, but it's plenty large:
Then I pulled apart a cat muffler from a 42cc. I added a larger outlet to the tiny port that was there:
I see no reason this won't flow fine. So this muffler got put on my most heavily modified Poulan:
Now I expect the extra heat from the cats will cause me more vapor lock issues, especially on the 142 with the Turbo Clean scoop. On the 42cc saw I use this modified cover to reduce vapor lock, and it works quite well:
I ran a tank through both saws cutting hickory today, and they ran just as they always have. They didn't stink so much though.
