MS201TC won't idle or start on choke

[tool11132]

I have a ms201tc m tronic saw that won't start on choke or idle at all. It will only start on full throttle off choke and run on full throttle to mid throttle then cuts out. I have replaced the fuel filter, and installed a new oem carb with fuel solenoid. I cannot get it to start on choke in order to do the mtronic reset. The exhaust screen is clean and the spark plug is newer. Fuel is new and the proper mix. I have not replaced the coil module as it seems to be fine and produces spark. Any advice would be greatly appreciated.

 

[ballisticdoughnut]

Have you performed a vac/pressure test? I’ve seen torn intake boots on those saws from being dropped out of a tree. Also remove fuel filter and pressure test. Could have a leak in fuel hose. Have you done compression test? Pulled muffler to inspect piston?

 

[tool11132]

compression about 115, pressure and vac tested tank through vent hose, also vac and pressure tested vent on its own. Do you know if there should be any resistance changes on the red / black wires on the coil that go to the fuel solenoid measured at the coil connector? I was able to get the saw to run with no blade on choke for about 45 sec then full throttle and it idled for a few sec then shut off and would only start again on full throttle. I have the 1145-120-0622 carb with white solenoid with 1145 4703A coil incase that means anything. I looked inside the intake boot with the carb off but did't see any cracks and I removed and tested the impulse hose and it was good also.

 

[ballisticdoughnut]

115 psi compression is low for that saw, but that could be due to the tester your using. Should be 150+.

 

[Tobystihl]

My go to fix is replacing the wiring loom when the saw stops after a few seconds.

 

[ZeroJunk]

115 psi compression is low for that saw, but that could be due to the tester your using. Should be 150+.

Yes, pull the muffler and look at the piston as he suggested.

 

[stihltech]

Diagnosis time. Just like any saw. Start from the beginning. Truthfully. The computer hookup is the last thing you need right now.
Had many a carburetor on those, but you must verify integrity of the whole saw first.
Does the inlet needle hold pressure?

 

[tool11132]

Have you performed a vac/pressure test? I’ve seen torn intake boots on those saws from being dropped out of a tree. Also remove fuel filter and pressure test. Could have a leak in fuel hose. Have you done compression test? Pulled muffler to inspect piston?

I did a hot compression check and it was 90 psi after an extended full throttle run, vs 115 psi cold. I am assuming this why it won't idle or restart easily once its hot without full throttle.

 

[Tobystihl]

Sounds like you've sussed the problem!

 

[ballisticdoughnut]

I did a hot compression check and it was 90 psi after an extended full throttle run, vs 115 psi cold. I am assuming this why it won't idle or restart easily once its hot without full throttle.

Use the same compression tester on a known good running saw. Something isn’t adding up here, those numbers are way too low. Or pull the muffler and inspect the piston. If it’s scored you’re looking at a full rebuild.

 

[Twinfield]

My experience with those saws is any little bit of scoring of the piston and/or cylinder will cause that issue.