sun64
ArboristSite Operative
I purchased a US 660 in Australia. I ditched the US muffler and put on a dual port. What a waste of time they are. No wonder the saws hardly go.
I used a 1/4 carbide bit in a drill and opened up the small holes in the internal cage.
I ground 4 of the small holes into a 5/8 x 3/4 hole. I did this on all 3 sides of the cage where the small holes were.
I then drilled a 5/16 hole in the upper end of the front baffles plate.
I opened up the side hole on the dual port as well and replaced the tiny mesh with 2mm stainless steel screen I have here.
I also matched the muffler to the gasket.
I left the front baffle plate in place , except for the small hole I drilled in it to help put a bit of backpressure back into the cylinder.
The rest is preety gutted though.
My guestimate is with the larger mesh, I am at around 95 % of port opening. 85 to 100 % is all you need .
I have never started a fire with my larger mesh. I only put it in to keep the wasps out from making nests in there.
Hope this helps, but those stock mufflers are way too restrictive for the saw.
I also changed out the main jet in the carb , from a 62 to a 74.
A lot more power now.
Wayne
I used a 1/4 carbide bit in a drill and opened up the small holes in the internal cage.
I ground 4 of the small holes into a 5/8 x 3/4 hole. I did this on all 3 sides of the cage where the small holes were.
I then drilled a 5/16 hole in the upper end of the front baffles plate.
I opened up the side hole on the dual port as well and replaced the tiny mesh with 2mm stainless steel screen I have here.
I also matched the muffler to the gasket.
I left the front baffle plate in place , except for the small hole I drilled in it to help put a bit of backpressure back into the cylinder.
The rest is preety gutted though.
My guestimate is with the larger mesh, I am at around 95 % of port opening. 85 to 100 % is all you need .
I have never started a fire with my larger mesh. I only put it in to keep the wasps out from making nests in there.
Hope this helps, but those stock mufflers are way too restrictive for the saw.
I also changed out the main jet in the carb , from a 62 to a 74.
A lot more power now.
Wayne