Chainsaw adjustment question...

[Mrleft8]

Something got out of whack when I had to replace the fuel line on my Stihl 038 super, and I can't seem to get it back into whack. It was running perfectly (aside from the gush of fuel mix at one point) and now in order to cold start it, I have to crank the main idle screw all the way in, then back it off 2 turns. But at this setting it races like crazy once it warms up, so I open the main idle screw to 6 1/2 turns until it idles normally... Obviously I've got something wrong with either the fast, or slow idle screws.....But what? (It won't even think about cold starting with the main idle screw at 6 1/2 turns)

[ 11-27-2005, 09:06 AM: Message edited by: Mrleft8 ]

[Ken Hutchins]

First, the fuel line replaced, why, some small bits of the fuel line or filter may be in the carb. 2 turns on the low speed mix should be close, definitely not 6 or so turns. When you replaced the fuel line did you remove the carb? When replacing it the idle speed set screw may have gotten bent if the throttle linkage wasn't held away from the screw when tightening the carb. If this screw is bent it will make you think the mixture adjustment is off when actually the idle speed adjustment has problems. The other place for starting problems is the carb inlet needle and diaphram; a bad needle, burrs or worn areas on the needle lever or diaphram button can cause the needle to hang tight instead of letting in fuel, or the diaphram itself might have problems. If it cold starts ok but starts hard when warm or guits after running a while, the fuel vent might be plugged. This is only a few things to look at, there could be a bunch of other causes. :rolleyes:

[Mrleft8]

The fuel line ruptured due to.... er.....fatigue I guess..... It was kinda like an old used rubber....Very thin and flimsy. I did remove the top of the carb, but it wasn't necessary to remove the whole deal. Which is the hi and the lo on a Stihl? There are 3.....The big main idle, then below that 2 lil ones....

[Del Lansing]

Is there a kink in the fuel line maybe?

[Stiletto]

Have a look at the filter in the fuel tank.

[Mrleft8]

No kink and the filter is brand new spanking clean. It's definately something out of adjustment on the carb. Once it's warm it starts first pull. It's also guzzling gas at this point because it's running so rich.

[Ken Hutchins]

The big main idle is speed only, the 2 little ones are mixture, the one closest to the intake is hi, the one closest to the engine is lo.

[Mrleft8]

So I want to open the lo, and close down the hi?

[Mrleft8]

Ehem! (Where's Smalser when you need him?)

[Ken Hutchins]

Start with both mixture screws open 2 turns, get it started and warmed up. Adjust high with saw running max, adjust mixture to get the highest speed then turn counter clockwise till it slows down somewhat it must run a bit rich on high or you will burn the piston. After getting high speed set adjust low mixture the same way, increase to highest speed then back it off the make it richer. Finally set the idle speed low enough so the chain will stop on idle. After you think you have it all set redo this sequence once or twice because changing the low settings could affect the high settings. A rich mixture is better for the life of the saw, a lean mixture could cook the engine in just a few minutes of running.
2 other things to do before adjusting the carb, make sure the air filter and the screen in the exhaust is clean.
Once you finally get the mixture screws set NEVER adjust them again. When the saw has problems it is usually something else causing it, unfortunitely most people start readjusting the carb instead of finding the real cause of the problem. I ran my Stihl 25 years without touching the mixture screws, changed the inlet needles diaphrams and gaskets several times, done the same thing with the Jonsered on my mini mill. NEVER touch the mixture screws.

[Mrleft8]

Thanks Ken!