Stihl MS200 bogs down at throttle

[Thunderhead]

Hi.

I inherited a Stihl MS200 2007 model from my father. He used it in the woods and after leaving the saw for a few minutes to do some small things, he was not able to start it again. I have been able to make it run, but it does not run properly and I need some guidance.

In short, now it starts easily and runs fine at idle, and responds well to quick pressure on the throttle, but with persistent throttle it starts to gargle as if the choke goes on (it does not), and it stops if I do not release the throttle (it will easily start again). If I release throttle early enough, it returns to idle. It does not matter where the H-screw is adjusted. The screws are adjusted according to the book after turning them a bit to see if it makes any difference.

So far I have:
Replaced carburetor, no change.
Replaced coil, no change.
Replaced spark plug, no change.
Replaced clutch, no change.
With or without air filter, no change.
Replaced fuel hose and filter, no change.

As a last resort, I took off the cylinder today and along the way checked the connection between the crankcase and the carburetor was open, and it was. The cylinder looks exceptionally fine and cannot feel the slightest wear edge after the piston rings, and the piston and rings themselves were also in excellent condition (ie no signs of soot in the groove of the rings and the rings were loose). Can also not feel any slack in rod bearings or crank bearings.

Almost the only thing I have not tried now is without a muffler, but it looks absolutely fine inside with insignificant soot here and there (does not have fine-mesh mesh as a spark arrestor).

I have not put it together yet, and hope that it may be that there was some blockage in the pipe or hose between the crankcase and carburetor that disappeared when I checked, because now I am starting to run out of ideas ....

Sorry for any confusion, English is not my native language.

 

[Vintage Engine Repairs]

Hey mate

It sounds lean. The quick (Initial) pressure on the throttle resulting In good throttle response is likley because you are actuating the accelerator pump (If present) giving the saw a shot of fuel. After that, as the engine rpms increase the seals are allowing more air past than can be compensated by tuning.

Really you need to pressure and vac test the saw, which will probably show your seals are leaking under vacuum.

With everything you have changed (so long as the parts have all been changed with OEM parts) a leak somewhere is your likely culprit and all the parts you changed were actually all ok. If you changed the old parts with new Chinese AM / clone parts, take them back off, put your original OEM parts on and bin the Chinese Clone ones.

Buy a vacuum and pressure gauge, it is cheaper than the parts you have already replaced (30 usd off ebay)

Uploading a video here will also help.

Warm regards, Tom

 

[Thunderhead]

Thanks for your reply Tom! Can you point me in the right direction of a suitable vacuum and pressure gauge? And where do you expect any leaks to be?

 

[SteveSr]

Thanks for your reply Tom! Can you point me in the right direction of a suitable vacuum and pressure gauge? And where do you expect any leaks to be?

Here is the link to the vacuum tester:
https://www.skf.com/mityvac/products/hand-vacuum-pressure-pumps/hand-pump-kits/mv8500Shop around for best price.

Leaks can come from just about any aged rubber including crankcase seals.

@lone wolf can tell you for sure but I believe that that some carbs that were use on this series had problematic accelerator pumps that would fail and cause air leaks through the carb. I would sort this out first. 2007 is kind of new to see failed seals and rubber.

 

[lone wolf]

Here is the link to the vacuum tester:
https://www.skf.com/mityvac/products/hand-vacuum-pressure-pumps/hand-pump-kits/mv8500Shop around for best price.

Leaks can come from just about any aged rubber including crankcase seals.

@lone wolf can tell you for sure but I believe that that some carbs that were use on this series had problematic accelerator pumps that would fail and cause air leaks through the carb. I would sort this out first. 2007 is kind of new to see failed seals and rubber.

I think I read he replaced the carb, the question is with what specifically new, used, or china aftermarket? Next step may be pressure vac test .

 

[Vintage Engine Repairs]

As above leaks can be on any mating surface, connection or rubber parts. Fuel lines, carb gaskets, cylinder and case gaskets, manifolds, oil seals, o-rings, spark plug hole, decomp valve, cracks or pitting. This is why the pressure and vac tool is essential

 

[siouxindian]

you pulled the cylinder?

 

[siouxindian]

you got it tore down now .just rebuild it .

 

[belgian]

As lone wolf said, tell us what replacement carb you installed. was it aftermarket or original stihl (which N°). The MS200 is a bulletproof saw, but the carb issues are well known (search for carbitooter thread).
I can only think of the carburator being culprit with the problems described

 

[Thunderhead]

Thanks for all replies!
Today I put it all together and surprise, it was just the same.... Maybe a little better when it was all cold, but I don't want to rev too much from cold. Tried it for about 5 minutes and was basically as before. Then I took off the oem carb and replaced it with the new china-carb and now it runs quite different. It hesitates at throttle, but when the revs comes up it revs pretty good until about 80% full throttle. More than 80% it gargle like before and the revs goes down. Playing with the throttle I actually think it's possible to use it for smaller jobs.

Reason why I went for china parts is that I don't know for sure where the fault is, so instead of wasting a lot of money on genuine parts, I try cheaper parts first to see it makes any difference.

 

[siouxindian]

you should just rebuild it.you proly just going to burn it up running it the way it is. it proly got a air leak.

 

[Vintage Engine Repairs]

Hi, don’t run it, fix the issues. It’s got an air leak you need to find. If not, you may very well burn it up!

 

[Thunderhead]

I called a local repair guy today to ask if he had tools to pressure/vacuum test my saw. After telling him about the problem with the saw not wanted to run properly on throttle, he was convinced the carb needed adjustment. So I took the saw to him and initially it behaved as earlier. He tried to do some adjustments but couldn't figure it out. Then he took off the plastic thingy that limits the turns of the H-screw and after some tries the saw revved as high as I've ever heard. With some fine tune, it has no hesitation on throttle and revs as smooth as a 2-stoke can do. Not sure if the guy adjusted the screw outside the previous limits or by doing so some debris was able to pass.

Thanks for all support!

 

[SteveSr]

I called a local repair guy today to ask if he had tools to pressure/vacuum test my saw. After telling him about the problem with the saw not wanted to run properly on throttle, he was convinced the carb needed adjustment. So I took the saw to him and initially it behaved as earlier. He tried to do some adjustments but couldn't figure it out. Then he took off the plastic thingy that limits the turns of the H-screw and after some tries the saw revved as high as I've ever heard. With some fine tune, it has no hesitation on throttle and revs as smooth as a 2-stoke can do. Not sure if the guy adjusted the screw outside the previous limits or by doing so some debris was able to pass.

Thanks for all support!

Compensating for an air leak with a carb adjustment? The leak will only get worse and burn up the saw.

 

[lone wolf]

Compensating for an air leak with a carb adjustment? The leak will only get worse and burn up the saw.

Those saws usually run perfect with a OEM carb at 1 turn out on each the H and L , depends on his elevation IDK what that is..

 

[Vintage Engine Repairs]

The number of turns out will say all that’s needed to be said. Less than 1 & 1/2 turns, I’d not suspect any issues and just say, you didn’t tune it properly.

Over that and yes he’s just compensated by adding more fuel.

Turn both the low and high screws in and count how many turns it takes until the screws rest on their seats and let us know. Hopefully he’s left the limiter screws off, though doubtful.

If not, take them off yourself first, then do the above.

 

[Thunderhead]

H - 1 and 1/3 turn out
L - 5 turns out
LA - 3 and 1/4 turns out

Living about 150 meters above sea level.

 

[lone wolf]

H - 1 and 1/3 turn out
L - 5 turns out
LA - 3 and 1/4 turns out

Living about 150 meters above sea level.

OEM carb ? Who ever adjusted it like that and thought it was alright is wrong! You could have an airleak. Dont use it like that!

 

[Thunderhead]

OEM carb.

 

[lone wolf]

OEM carb.

Big airleak, rip it down and pressure test it.