Stihl MS200t

[H-A]

I thought I should get one of Stihls best ever saws.

 

Arrived in the post yesterday, wow what a nice saw.

 

Loads of power, very light, now I can see why they are so well thought of.

 

As the new saws idle was a little fast (chain just moving), I backed off the idle speed screw, but that made no difference to the idle speed.

 

Could there be an air leak? main seals perhaps?

 

Thanks

 

H-A

[2stroke-ady]

It could be so many things! Air leaks normally make 2 strokes unstable, impossible to keep in tune. Are you sure it is a high tickover and not weak clutch springs causing the clutch to drag?

[Rich2484]

could be, try adjusting the low screw a small amount out, or just check its at factory setting.

 

low screw adjust first, then look into seals etc if this makes no diff.

[H-A]

I have a good speed range adjustment on the low screw, rich through to lean.

 

If I adjust to best running on the low screw, then the revs are too high and I can't back off the idle screw to adjust the tick over.

 

The only way I can make it tick over well is to richen up the low screw.

 

On all of my other saws and disc cutters, I set the "L" screw first to best speed, then back off the idle adjustment screw, to the desired idle speed (no chain or belt movement).

 

New one for me.

 

H-A

Edited September 24, 2013 by H-A

[Rich2484]

ok. go with the other post then, look into clutch, a creeping chain can be clutch springs worn. look at them first, see if any are broken, would be worth replaing anyway.

[spudulike]

I have a good speed range adjustment on the low screw, rich through to lean.

 

If I adjust to best running on the low screw, then the revs are too high and I can't back off the idle screw to adjust the tick over.

 

The only way I can make it tick over well is to richen up the low screw.

 

On all of my other saws and disc cutters, I set the "L" screw first to best speed, then back of the idle adjustment screw, to the desired idle speed (no chain or belt movement).

 

New one for me.

 

H-A

 

 

 

This is sounding like an air leak to me - reason for this is that if you undo the idle adjuster to the point it doesn't do anything, the throttle valve is either stuck open or the engine is getting air in from elswhere.

 

I had a 630 Jonsered once and that was exactly the same - I found the crank seal had actually dissintegrated completely!

 

Try setting the L screw one turn out from fully in and then undo the idle screw - if this still gives a faster than normal idle then take the side rubber grommet of the side of the airbox, start the saw and physically push the carb throttle arb close with your thumb and see if the revs drop - it is possible the throttle mechanism is catching or a bit sticky and if the revs continue being too high - it has an air leak.

 

Continuing to run the saw like this may cause damage - a good engineer should be able to pressure/vac check the saw to ascertain where the leak is.

[spudulike]

Looking at your post again, you DON'T adjust the L screw for highest speed, this is running lean, you bring the L screw in till the revs race and then back off circa 1/4 turn and then adjust idle.

 

Give it one turn out and see if that settles it

[H-A]

ok. go with the other post then, look into clutch, a creeping chain can be clutch springs worn. look at them first, see if any are broken, would be worth replacing anyway.

 

I would say the clutch is fine, the only problem is that the Idle speed adjustment screw has no effect at low revs.

 

I can reduce the revs by richening up the low speed screw, and there is no movement of the chain

 

It can't be correct that I should adjust the idle with the low speed mixture screw.

 

If that is normal practice for tuning this saw, that is great I will not strip the crank out and replace bearings and seals.

 

I just seems a little odd that I cant back off the idle adjusting screw enough to stall the motor.

 

H-A

[Rich2484]

give spuds idea a go. the low screw will adjust the idle speed, in will make it run fast, also lean it out, not a good place to have it.

 

out will lower the idle as it will run rich. the balance on standard is one turn out.

 

what colour is the spark plug?

[H-A]

I did remove the grommet an look to see if there was a problem with throttle movement, but it was closing fully.

 

That is what made me think of crankcase leak, I am more used to bronze outboard main bearings.

 

Steep learning curve, if only I could make one of my British Seagull racing engines rev to 12,000.

 

Now I need a 0 to 1 atmosphere vacuum gauge.

 

I might just replace the main bearings and seals, good place to start.

 

H-A