Posted by igore on April 21, 04 at 08:49:32:
In Reply to: Re: Carb tuning... posted by ICON on April 21, 04 at 05:21:12:
Your saw sounds like the low speed jet is plugged or set too lean.
There are three adjustments on the carb. Idle speed, low speed jet, and high speed jet.
Tightening the idle speed screw makes the saw idle faster. As long as the chain doesn't move when idling, set it as fast as you can to keep the engine from dying.
Loosening the mixture screws opens the carb jets wider and makes the saw run richer.
Set the high speed jet so that it is just shy of four stroking (running rough)at full throttle. This keeps it from running lean. Sounds like your saw is fine here.
Set the low speed jet so that the saw doesn't hesitate when you mash down the throttle. This may be your problem. If backing out the screw doesn't cure things, try putting it in all the way and backing it out about 1 1/2 turns. This will sometimes clean the jet holes.
Set the idle speed so the saw doesn't die when idling.
These are actually very high performance engines with an emphasis on power/weight. This makes them pretty high strung and sensitive to carb adjustments.
I find that these saws are so critical on adjustment that they are weather sensitive, needing readjusting between winter and summer to compensate for air density or something.
A saw that is set right for winter will run rough (rich) in the summer. Going the other way, a saw adjusted for summer air will hesitate in the winter when the throttle is mashed. The adjustment for season is usually about 1/8 to 1/4 turn.
If the saw doesn't start with the choke on and has a dry plug, check the filter in the gas tank. It is fuel starved. Also check that the linkage from the choke lever to the choke isn't out of adjustment. There's a lot of vibration in these things to knock stuff loose.
This pretty much applies to old snowmobiles, outboards, and 2 cycle lawnmowers too.
: While we're on the subject, i have an old Husky 35 chainsaw that's been a real bear. It's only a small saw for misc projects when i don't want to trash the new one. The problem is it's really tough to get it started, need to be pulled at least a dozen times full choke, even when 90 out. I believe the plug is dry if removed so it seems it might be lack of fuel. Compression is good, new plug, clean air filter, fresh gas. Once it does start, i need to lightly feather the throttle to keep it running but too much and it'll die. Once running it runs great WOT but if yoy let up on the gas it'll die right out and wont restart till it cools all the way down. I've torn the carb apart and put new gaskets in plus tried setting it to factory specs but it still wont run right. Do you think the float setting, or what ever it's refered to in 2 stroke engines needs adjusting and how do you set it?
: You mentioned it's really easy to set these too lean, how do you NOT set it too lean, hi idle adjustment or lo? What i usually do is try and set them to factory then minor adjustments to get it sounding good. I also heard that it's better to set the high idle first then low, but this is in regards to an old outboard motor so i don't know if it'd apply to all 2-strokes. Thanks for any advice.