Help MS 311 won't run right after rebuild

[stihltech]

So you have now performed the basic testing required for confirming a motor has no issues that would cause it to run poorly. This is exactly what a Stihl diagnosis chart (and any other 2 stroke manufacturer that provides one) is for. Now you get a carburetor and fix the saw.
Fixing carburetors is a 50/50 or less success. Corrosion inside cannot be removed by cleaning (passages). As rutterbe stated above, the carb is the final issue. Not an electrical computer, but a mechanical controlled by vacuum. Take away that control and you end up with bad operation or worse (scored piston and cylinder.)

 

[Gomofast]

I ordered the carb. I believe I found the problem within it. I think the tiny brass check valve under the metering diaphragm is bad. As I understand, it should allow fuel to flow from the metering side through the main jet into the throat of the carb. But I found that I could both suck and blow air through that little check valve - which means that it's not preventing air from coming back into that metering area when the diaphragm lifts. I think (hope) that makes sense.

 

[Gomofast]

Yep, new carb did the trick. It purrs now. Thanks all for the help.

 

[lone wolf]

One thing I've never been able to get my grasp around is how saw owners manage to straight gas any saw. I always keep my pre mix in a dedicated gas can and my straight gas for the 4 strokes in separate gas cans not anywhere near the pre mix can.

Working part time at my tractor dealer who is also an Echo dealer, I see a lot of straight gassed saws come in and I always wonder about the owners and their level of intelligence.

When the carb was done, was it rebuilt and just cleaned and were the internals reset properly?

By lending them out is one way!

 

[Husky77]

Mityvac is the way to go, dont spend hours looking on ebay for a cheap one because there are so many "cheap deals" you will end up with a kit in a red box that you think was a bargain until you use it, and find readings very erratic so first as last buy a good one. But as mentioned above, a drum of water will get you by and show a leak very well.
Are you 100% sure its straight gassed, could be something simple like a very dull chain and inexperienced user.
That's why you never lend your tools.

 

[cookies]

A quality tester is key, a couple adapters are also key for making things reliable and able to find the tiny leaks. The check valves in those ms290-311-390 carbs deform flooding or starving the L circuit that will make starting difficult and roach pistons, the older versions on the 0 series were not so prone to the check valve failures. Some of it is the exceedingly long life these saws seem to live.