064 fast idle ?

[wi50]

I picked up a good running 064 and put some time on it, then I simply added a couple holes in the side of the muffler, made a little deflector and tig welded it on. I'd have to look at it again and see what size I made the holes, but I figured the area of the existing exhaust hole in the muffler and the approxamate area of the exhaust port at the piston. Then I added the 2 holds to make my total exhaust outlet area roughly 80% the area of the exhaust port at piston. I ran it and re tuned the carb.

The saw runs great and pulls verry strong in the cut, but comeing out of the cut it idles fast. If I start the saw and let it idle it will idle like it needs to. I also don't notice any change in the low speed mixture adjustment on the carb unless I really choke it off to probably 1/2 turn from closed, of course than it leans out and dies. The throttle plate idle adjustment is closed all the way and the saw will still idle fast.

At times I can adjust the carb and get a good idle, and at other times it just likes to run fast, a random problem.

Vaccume leak? or should I close off the additional holes in the muffler and see what happens. My muffler was in tough shape anyway, I took an hour and blasted it, tig welded the cracks and added some metal to make it good rather than buy a new one. I did not do any porting or take anything else apart on the saw, it makes roughly 150-160 PSI compression.

 

[blsnelling]

You want 125%-150% of the area of the port at the piston. The 80% comes from guys that go by the area at the flange where the muffler bolts on. But that's too vague. It's best to measure the port at the cylinder as you did. You just need to go bigger.

 

[wi50]

Looking (without measureing) at my neighbors new MS660, the area of the hole in the muffler is probably 1/2 the area of my old stock 064 muffler. His is the stock single port muffler.

Then I added the 2 more holes at roughly .400 to .500 in diameter each, I'd have to go measure as my memory works like a homelite. If anything I was figureing that the exhaust outlet is to large, makeing the idle fast. But it is way shy of the 125% exhaust port volume, or the 85% at piston volume.

I have a 066 mag with the dual port muffler that will be here in a few days, maybe I'll simply swap that muffler on the 064 and see what happens.