MS270 need help. please!

[fuzzybear]

  Symptoms:
   At wide open throttle it seams like it starts to lean out.
   When you release the throttle it runs at a very high idle then falls back to a normal idle.     This can last for up to 30 sec.
    I only have to move it slightly to the side and it wants to shut off.
    if I nose it down slightly it runs high and then drops down low.
    This all started out of the blue. I keep the saw inside, so it's warm when I use it.
    I have had the carb apart to check it every thing is clean. I replaced the fuel filter, and checked it as best as I could and didn't find any cracks. Different fuel. New plug. engine is running a little lean on the plug. Checked the manifold between the carb and jug found no cracks. cleaned out the tank vent.
    The saw is only a year and maybe 100 cords old. Any one know what's causing this or can give me a little direction?
Thank You
FB

[shinnlinger]

You say you had the carb apart, but did you put in a new gasket kit?  I just resurrected two old saws by simply putting the basic $6 kit (from Chainsawr) in.  As Al explained it to me, the new ethanol gas is hard on the diaphragms so they need to be replaced more often and the fuel starvation issue you mention could easily be caused by a weak diaphragm.

Good luck!

Dave

[ladylake]

 
It could be the crank seals or base gasket also but go through the carb, fuel lines first.
If you had the saw sitting for a while with ethonal laced fuel I'd think a dirty carb, they can be hard to get clean once clogged up.      Steve

[nmurph]

you have an air leak. i would replace the fuel line, and i don't know if it has one or not, probably does, the impulse line. those are quick and easy.
when you say you checked the manifold, did you flex it and check it carefully? sometime small cracks won't show unless the boot is flexed.
lastly, a pressure/vacuum test on the crankcase should be done. you may have a crank seal which is failing.

[SawTroll]

I am thinking air leak. Of course it could be related to the fuel system/carb as well.

Don't run the saw until it is diagnosed and fixed!

[lumberjack48]

It sure sounds like a air leak, every time i had this happen it was the boot, the clamps loused up. I tightened them up and it ran perfect, never now it might be this simple.

Start the saw, take a can of starting fluid and spray a little any place it could have a air leak, if it revs up you found it, a very simple way to check for air leak.