Stihl ms200t erratic idle

[john.massing]

I ran my ms200t this morning on a removal and it worked well. This afternoon, i was cutting a larger branch and the idle went up. Seemed like it leaned out or had an air leak. I shut it off. Later I pressure/vac tested it because i suspected an air leak, but it held pressure and vacuum. I checked the carb and it looked clean, screen was clean, diaphragm supple, etc. I blew it out and cleaned the air filter. When I fired it up the idle still seemed a bit high, so i backed out the LA and richened up the low jet and checked it against a tach. Seems fine now. I think the weather was cooler and less humid this afternoon. Does anyone think that could be the cause, or are there any other suggestions? Come to think of it the throttle spring on the butterfly could have been gummed up. What do you think?

 

[MA Arborist]

I know that the intake boot is prone to failure on the 200t. I’m not sure but the boot may have a crack and the vac test may not show while the saw is sitting on a bench.

I’ve replaced a lot of intake boots on mine and the crack is usually closed unless the top handle is pulled.

 

[john.massing]

Thanks. The intake manifold is pretty new and OEM. The next time I run the saw i will move the handle around and see if I can get it to act up. I moved it in all directions last night after I tuned it and it seemed fine. I will keep an ear on it. The suggestion is much appreciated and if you have any others, please pass them on.

 

[MA Arborist]

Thanks. The intake manifold is pretty new and OEM. The next time I run the saw i will move the handle around and see if I can get it to act up. I moved it in all directions last night after I tuned it and it seemed fine. I will keep an ear on it. The suggestion is much appreciated and if you have any others, please pass them on.

I’m not sure what else. Besides the carb going bad after a few years and the torn boots I never had any other problems with the 200ts. If I think of something I’ll definitely let you know. …

 

[john.massing]

Carb is new too! Lol i will keep an ear on it, we had a wild shift in temperature and humidity...idk. thanks

 

[evo]

In take boot or tank vent would be my guess

 

[Chris Schultz]

Sounds like my 200t when the impulse hose needed replaced….

 

[john.massing]

It is holding pressure and fairly new and supple, but thanks, I really appreciate the suggestions.

 

[Bart_]

New carb rules out air leakage via the accelerator pump - I think?

 

[john.massing]

Indeed that is why it has a new carb...lol. after adjustment, It may get run tomorrow and we'll see how it runs. I didn't get the opportunity to run it today.

 

[john.massing]

Thanks for all of the suggestions. I ran the saw today and it ran well other than me adjusting a tad on the rich side. The symptoms acutely happened after cutting a sugar maple limb with wetness inside. Maybe some got on the throttle spring with other gunk and slowed the butterfly's action. I really don't know and this is speculation. That fact is that the saw passes all my diagnostic tests, runs wot without fluttering, and idles smooth and unwavering through all the motions. Thanks again.

 

[Bart_]

If you get tired of or can't get an accelerator pump carb there's always the Marc Antoine epoxy block off trick. Only drawback the epoxy eventually goes soft and needs a re-do. And you don't get the instant rev response.