Stihl ms201t idle out of control

Karstensklaywerks

Karstensklaywerks

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I have recently rebuilt an older Stihl ms201t and now I cannot slow the idle down! I have installed new piston rings and ported the muffler. The only re-conditioning I did to the carb was to replace the plastic metering diaphragm and on the other side, the rubber pump (diaphragm). It starts easily and cuts like a beast but I cannot adjust the idle down. The LA (idle adjustment) screw has been backed all the way out so it is not even touching the throttle stop. I have made minor and major adjustments to both hi and lo screws, starting at the owners manual suggested settings, but does not alter the idle rpms very much at all. I am not using a tach on it, just going by sound and how fast the chain is turning. At this point the idle appears to be nearly a third throttle, too fast to be safe with the chain turning so fast at rest. What have I done to this beast?! Also, the "hi" carb screw has a plastic limiter which gives me barley half a turn either direction. It is a stock, Stihl/ZAMA C1Q, S280 carburetor.
 
stihl86

stihl86

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I agree with the possible air leak. I'd stop using it till you figure it out. You sure you put the two flanges back on the intake manifold? One goes on the outer perimeter and the other fits into the manifold.
 
Karstensklaywerks

Karstensklaywerks

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I will be checking for air leaks tomorrow. I suspect it may be the intake manifold boot which I had difficulty feeding back through the black plastic carb retaining plate. Yes, I did install the lower rubber flange, made sure it snapped down tight and flush. The upper boot flange, where the carb seats into, is not separate, it is built into the boot itself. Although the manifold seemed flexible and soft, I wonder if I didn't tear or crack it fitting it back thru the retainer plate. I recall being quite frustrated that it was do difficult to do, thinking it was an ignorant design. I think I have seen older 201 models which use a separate ring- type flange that fits down into the manifold boot, which is a much better design.
 
stihl86

stihl86

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There’s nothing wrong with the design. In fact it a better set up Wrap a piece of recoil rope around the manifold, pass the tag ends through the opening in the handle and gently pull the manifold through.
But it’s pretty hard to rip the manifold.
And the inner flange can come off the carb if your not careful. It’s only a push fit into the recess.
There is a tiny “key” on it to maintain a correct fit.
 
Karstensklaywerks

Karstensklaywerks

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Gentlemen, success! Thank you for your help and information!!
I was in agreement about the air leak so I focus my efforts on that. I carefully disassembled down to the manifold. Took it off and inspected it thoroughly; it is in great shape, very flexible still. I carefully took the carb apart also.
I found two suspect issues. Manifold- the mating surfaces between manifold flange and cylinder were oily, not clean. I wiped and cleaned the two surfaces and reinstalled the manifold. Carburetor- I discovered remnants of the old paper gasket on the fuel metering side which could have caused air leak. My fault for being in a hurry when I rebuilt the carb and not cleaning all mating surfaces carefully.
That seems to have been the problem(s)! I started it up and the idle was adjustable again. In fact, stalled out because I had back the idle adjustment screw all the way out, lol! But I was thrilled because I knew I had it licked; quickly re-adjusted idle screw and adjusted "hi" slightly off factory settings due to freshly ported muffler. Haven't cut any wood with it yet but I am confident it is better than new. My client raves about this saw. I really am impressed with it! Super fast and lightweight, I need to find me one!
Thanks Stihl86 for the tip about feeding manifold through handle port! I will take your word that it is a superior design
I want a 201 now!!!
 
Mad Professor

Mad Professor

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There’s nothing wrong with the design. In fact it a better set up Wrap a piece of recoil rope around the manifold, pass the tag ends through the opening in the handle and gently pull the manifold through.
But it’s pretty hard to rip the manifold.
And the inner flange can come off the carb if your not careful. It’s only a push fit into the recess.
There is a tiny “key” on it to maintain a correct fit.

It's better to use a thinner string. Acrylic knitting yarn works great.
 

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