Ongoing MS 200T Carburetor Issue

[ZeroJunk]

ZeroJunk: How do you go about making sure that the butterfly is replaced "...in the exact same position?" opcorn:

You can go by the mouse hole in relation to the idle orifice, or mark it. The butterfly is not round, so if you are off much it will not close all the way. And, just a hair will make it idle too high. It wants to turn when you tighten the screw.

In looking at your photo, does it have a nipple on the shaft to keep it in place? The one I repaired did not.

Never mind , that's the choke side.

 

[lone wolf]

What is the compression reading on that saw?And try fixing that carb first if no good pres / vac test then as a last resort buy a new one . To bad you cant stick a known good runner on and see what happens!

 

[HandLogger]

Marking the position of the butterfly valve

You can go by the mouse hole in relation to the idle orifice, or mark it. The butterfly is not round, so if you are off much it will not close all the way. And, just a hair will make it idle too high. It wants to turn when you tighten the screw.

In looking at your photo, does it have a nipple on the shaft to keep it in place? The one I repaired did not.

Never mind , that's the choke side.

We own and manage forest land, ZeroJunk. I'm not a Stihl repair tech, so I'm not familiar with all of the parts of a Zama diaphragm carburetor.

Do you happen to have any photos or diagrams of the parts you're referring to? I'm familiar with the butterfly valve on the engine side of the carb, but the "mouse hole" and the "idle orifice" are terms I'm unfamiliar with.

Thanks for your time,
HandLogger

 

[HandLogger]

Compression and/or vacuum testing

What is the compression reading on that saw? And try fixing that carb first if no good pres / vac test then as a last resort buy a new one . Too bad you cant stick a known good runner on and see what happens!

Do you have to own a special tester (from Stihl) to test the compression of the MS 200T, Lone Wolf?

Does the vacuum test require a Stihl test system of some kind?

 

[ZeroJunk]

We own and manage forest land, ZeroJunk. I'm not a Stihl repair tech, so I'm not familiar with all of the parts of a Zama diaphragm carburetor.

Do you happen to have any photos or diagrams of the parts you're referring to? I'm familiar with the butterfly valve on the engine side of the carb, but the "mouse hole" and the "idle orifice" are terms I'm unfamiliar with.

Thanks for your time,
HandLogger

The fuel that the saw idles off of comes out of one, two, or maybe even three tiny holes, depending on the carb, in the barrel of the carburetor on the engine side of the butterfly. The main fuel nozzle is on the far side of the butterfly from the engine.

If I remember correctly that carb has one idle hole in the barrel for fuel to enter and a mousehole centered over it in the butterfly so it can get some air to atomize it.

 

[lone wolf]

Do you have to own a special tester (from Stihl) to test the compression of the MS 200T, Lone Wolf?

Does the vacuum test require a Stihl test system of some kind?

A snap on tester for comp and a mitivac 8500 for pres/vac

 

[HandLogger]

Thanks for the carburetor primer

The fuel that the saw idles off of comes out of one, two, or maybe even three tiny holes, depending on the carb, in the barrel of the carburetor on the engine side of the butterfly. The main fuel nozzle is on the far side of the butterfly from the engine.

If I remember correctly that carb has one idle hole in the barrel for fuel to enter and a mousehole centered over it in the butterfly so it can get some air to atomize it.

Thanks for the helpful information, ZeroJunk.

I'll take a real close look for what you're describing the next time I have the carburetor off of the MS 200T we're working on.

 

[HandLogger]

Test Equipment

A snap on tester for comp and a mitivac 8500 for pres/vac

I'll check into the test equipment you've mentioned as soon as I can, Lone Wolf.

I'm not sure what it is exactly, but the Mityvac 8500 sounds a little imposing.

Thanks again,
HandLogger

 

[pgg]

bah, ditzy 200T's, gone done a bearing, caused the seal to leak because of the extra slop, symptoms are running like a sick dog and hi revving idle no matter what the carb setting, the shagged bearing you can tap out easily with a socket or suchlike, easy to test the seals, seal the exhaust port with rubber and backing plate, just seal the inlet port with your thumb, slap your tyre pump to the impulse hose and stick some air in, you'll soon see the leak if there is one

 

[lone wolf]

Good for a pressure test .But to test the seals you need to put a vac on them because that is when a crank seal fails under vac.

 

[pgg]

Good for a pressure test .But to test the seals you need to put a vac on them because that is when a crank seal fails under vac.

hehe, no need, if they leak under pressure then it won't matter if they leak under vacuum or not ...

 

[lone wolf]

Troubleshooting Air Leaks

Once you've found a leak, fix it and retest. If it passes a pressure test, apply a vacuum. When it comes to leaks, vacuum is just as important as pressure. Some engines will hold 6 - 8 lbs pressure, but not be able to hold a vacuum. If you find this problem, suspect the main bearing seals.

 

[HandLogger]

Non-accelerator pump carbs for the MS200T

Definitely split the muffler and scrub it out, see if it responds to the trigger then, does sound like a blocked exhaust, also crank the lo AND hi jets rich as hell then gradually lean the hi back in so she's revving out good, fiddle the lo as well, might be just a case of tuning to get the little tart responding. P.S. non-accel carbs work perfectly on a 200T also

pgg: Above, please see a quote taken from a post that you made back in September of 2010 on a thread called about to toss the 200T over the hill.... Your last post to this thread indicates that you're having bearing and seal problems with your 200T, but I'd still like to ask you if, in the past, you tossed out a Zama C1Q-XXXX accelerator pump model for a Walbro, or perhaps for a Zama without an accelerator pump?

Please let us know how you know that "...non-accel carbs work perfectly on a 200T..."

The new carbs called for by Stihl are just too expensive, if they're simply the same design as the Zama C1Q-S61D (accelerator pump model) that's presently on our MS 200T.

Thanks for your time opcorn:

 

[pgg]

hey yeah, there's non-accel pump Zamas as well as WT walbros from 020T's, the 020T and 200T stuff, linkages etc.. all interchanges, you can tell the accel pump carbs from the hole over the butterfly shaft, also despite what some say, a fixed jet carb works brilliantly on a 200T, just need the right jet size in it to stop it from over-revving lean

 

[HandLogger]

Which carb would you take a chance on

My main concern, pgg, is that we'll buy the [read: expensive] carburetor presently recommended by Stihl -- the Zama C1Q-S126A -- only to find out that it's design is just as flawed as the carb that we're replacing, the Zama C1Q-S61D. For that reason, I'm all for trying out a non-accelerator pump carb.

It was recommended, earlier in this thread, that we might give a Zama C1Q-S16A a go. Apparently, it's a non-compensating carburetor intended for a Stihl 020T that will work in an MS 200T. I'm no Stihl repair tech, by any stretch, so I couldn't say whether or not the choke and/or the throttle linkages we presently have will work out or not -- and neither can the fellow that recommended the carb because he had the work done by a dealer. At this point, I also couldn't tell you whether or not the older version -- the C1Q-S16A -- is a non-accelerator pump model, but my feeling is that it's not. If we went this route, obviously, we would have to also get a new airbox backing plate designed for the older carb.

Having written that, I'm not opposed to trying a Walbro carburetor, either. I'm not sure what would have to be modified to get one to work in our sick MS 200T, but I'd love to read about it.

If you were replacing an S61D today, which type of carb would you buy and why? We would also be much obliged if you would care to comment on what modifications would have to be made to get the replacement carb to function properly.

Cheers

 

[a. palmer jr.]

Hi mate. No dramas for the help.
I didn't actually do the swap but one of the local Stihl dealers did. They did the mandatory epoxying of the accelerator pump etc but the saw continued to get out of tune, over rev etc etc. It was really running like a pig. Anyway I took it back in to the dealer and he replaced the carby and backing plate to an older setup he had in his workshop for free. It has not missed a beat since He told me that my issues had him stumped and he works on a lot of 200T's. They are a very popular saw here for fruit tree pruning and contract pruning companies.

I'll try to get some pictures and more information up ASAP.

Does the 020T have the same carb problems or is it different?

 

[pgg]

choke and throttle linkages are plug and play between 020T and 200T, the backing plate isn't an issue, the "compensator" is just a snorkle poking into the airbox, a normal non-compensator carb lid fits, you just seal up the hole in the backing plate

 

[MCW]

Does the 020T have the same carb problems or is it different?

No it didn't have the same problems. I've been led to believe that Stihl installed a more "advanced" carby on the 200T's and created more problems than they fixed.

I'm glad you got the photo linking sorted out Handlogger. Sorry I didn't get back to your PM to help out sooner.
ppg is correct in saying you can simply block the backing plate hole if going from a compensating carby to a non compensating carby.

Lone Wolf is also correct in asking about compression. My local dealer has told me before that he has seen 200T's with what looks to be carby problems be 100% fixed with a new ring and an increase in compression. This is a known Stihl dealer fix on low compression and well used 200T's. Our area has shown up a lot of 200T issues and this dealer in particular has a very good handle on them. Basically all of the 200T's in our area are used for fruit tree pruning (mainly massive almond orchards) and for months on end are running 8 hours a day, 7 days a week. One particular large corporate farm buys 20 at a time.

 

[HandLogger]

Lone Wolf is also correct in asking about compression. My local dealer has told me before that he has seen 200T's with what looks to be carby problems be 100% fixed with a new ring and an increase in compression. This is a known Stihl dealer fix on low compression and well used 200T's. Our area has shown up a lot of 200T issues and this dealer in particular has a very good handle on them. Basically all of the 200T's in our area are used for fruit tree pruning (mainly massive almond orchards) and for months on end are running 8 hours a day, 7 days a week. One particular large corporate farm buys 20 at a time.

Thanks for getting back on the thread, MCW. Although the MS 200T we're currently trying to repair has seen its fair share of use, you definitely use your top-handle saws a lot more than we do. We manage forest land for timber production mostly, so we use a top-handle saw when we're up in a given tree or when we have windthrow issues. We also fell timber, and produce cordwood on occasion, so we use a variety of saws depending on the job at hand.

The point is that -- although a reliable high-performance top-handle saw is critical at times -- we don't operate them all day long. That's why I was surprised by the failure of this particular MS 200T. It certainly hasn't been used as hard as our other Stihl saws, and I know that it's been maintained just as carefully. The 200T is just the right saw for the job -- when it runs well -- but it's clearly the least reliable Stihl saw model we've owned.

 

[lone wolf]

Thanks for getting back on the thread, MCW. Although the MS 200T we're currently trying to repair has seen its fair share of use, you definitely use your top-handle saws a lot more than we do. We manage forest land for timber production mostly, so we use a top-handle saw when we're up in a given tree or when we have windthrow issues. We also fell timber, and produce cordwood on occasion, so we use a variety of saws depending on the job at hand.

The point is that -- although a reliable high-performance top-handle saw is critical at times -- we don't operate them all day long. That's why I was surprised by the failure of this particular MS 200T. It certainly hasn't been used as hard as our other Stihl saws, and I know that it's been maintained just as carefully. The 200T is just the right saw for the job -- when it runs well -- but it's clearly the least reliable Stihl saw model we've owned.

The carbs are made in China you know.