MS 192TC Carburetor

[Carburetorless]

I bought a used MS 192TC.

The saw was hard to start at first, so I cleaned the carb, then I adjusted the H, L, and LA screws. Now it starts and idles(sometimes idles fast at first then smooths out), but when I pull the trigger the saw bogs down and dies.

The only thing I noticed that seems odd about the saw(other than the way it runs) is the primer bulb, it doesn't want to pop back out when I press it in, it sticks for a while then eventually pops back out.

I want to put a new carburetor on it, but I can't find one online anywhere(going to see a dealer tomorrow).

I'm convinced it's a carb problem, but I could be wrong.

I'm hoping that someone here can diagnose the problem better than I can. Do you think it's the carb, or is it something else?

Thanks

 

[stderr]

Primer bulb

The primer being sluggish could just be age; they're cheap to replace. When you cleaned the carb, did you disassemble it or rebuild it? How did you clean it?

You say you adjusted the LA, L and H screws. If you can't get the saw to wind up, how did you adjust the H screw? It should have a factory default position that's close to ideal (usually 1-turn out from bottomed) then you tweak from there. If the saw is dying, it's probably running out of fuel when you pull the trigger. Open the high jet a little more. If you can't get it, it could be something else. If you bottom the jet screws and back them off, be very gentle when you hit bottom or you may damage the jets. If you overtighten the screws you will need a new carb.

Checked compression? Pulled the muffler off and looked at the cylinder wall and piston?

I'm not sure if there's an impluse line on that saw, but if there is, could it be detached? Without it connected, the carb will not be able to pump fuel, and you won't get very far. You might be able to idle if you hold the saw at the right angle, but I'd bet it's pretty tough.

It could also be that the vent for the fuel tank is plugged, or partially blocked. If this is the case the saw might be able to idle but will sputter out pretty quickly due to a lack of air flowing into the tank to fill the empty space left by the fuel exiting.

There are lots of videos on youtube showing step-by-step rebuilding of chainsaw carbs, you should be able to do it fairly quickly and easily. Here's a good reference for tuning: Saw Carb Tuning

 

[JoshF]

dont forget the accelerator pump o-ring that leaks and causes the same problem. requires new carb to fix.

 

[speeco]

be sure to remove muffler deflector and screen to see if it is plugged with carbon . this was a problem i had recently.

 

[Carburetorless]

The primer being sluggish could just be age; they're cheap to replace. When you cleaned the carb, did you disassemble it or rebuild it? How did you clean it?

I took it apart, cleaned it, then reassembled it. I didn't put anything new in it.

You say you adjusted the LA, L and H screws. If you can't get the saw to wind up, how did you adjust the H screw? It should have a factory default position that's close to ideal (usually 1-turn out from bottomed) then you tweak from there.

I turned the screws all the way in, then backed them out, 1 full turn for the L, 3/4 turn for the H, and 1/4 for the LA.

The H will only turn out 3/4.

If the saw is dying, it's probably running out of fuel when you pull the trigger. Open the high jet a little more. If you can't get it, it could be something else. If you bottom the jet screws and back them off, be very gentle when you hit bottom or you may damage the jets. If you overtighten the screws you will need a new carb.

The L screw is stripped out a bit, someone may have over tightened it.

I'll try opening high jet more.

Checked compression? Pulled the muffler off and looked at the cylinder wall and piston?

I'm not sure if there's an impluse line on that saw, but if there is, could it be detached? Without it connected, the carb will not be able to pump fuel, and you won't get very far. You might be able to idle if you hold the saw at the right angle, but I'd bet it's pretty tough.

I haven't checked the compression, or the cylinder.

There is a line sort of behind the carb that a tube from the carb plugs into when the carb is placed back in, it has a spring on it(I guess to hold it up so the tube will go in), I made sure it was reconnected when I put the carb back in.

It could also be that the vent for the fuel tank is plugged, or partially blocked. If this is the case the saw might be able to idle but will sputter out pretty quickly due to a lack of air flowing into the tank to fill the empty space left by the fuel exiting.

I checked that, couldn't find anything.

So now the saw won't start at all, I checked/cleaned the plug, checked spark, spark is good, it throws an arc at least 1/4 inch to one of the carb bolts.

I'll put a carb on it and see what happens.

There are lots of videos on youtube showing step-by-step rebuilding of chainsaw carbs, you should be able to do it fairly quickly and easily. Here's a good reference for tuning: Saw Carb Tuning

Thanks

 

[ZeroJunk]

dont forget the accelerator pump o-ring that leaks and causes the same problem. requires new carb to fix.

You can buy that pump piston kit for $8.50. Just replaced one on a MS200 last week . Not the easiest thing to do for a beginner I don't suppose.

 

[Carburetorless]

dont forget the accelerator pump o-ring that leaks and causes the same problem. requires new carb to fix.

Where is the accelerator pump o-ring?

 

[galde]

The throttle rod has a flat spot that contacts a spring-loaded cylindrical piston that carries a tiny 0-ring. When you open the throttle, the piston is forced forward which pushes a small amount of fuel into the carb intake. These carbs seem to fail after extended use because the o-ring degrades and the piston scuffs the bore that it slides in. If the bore is scuffed, then a new o-ring will soon also fail. Do a search on "carbitooter" and get the whole story on this issue.

 

[Carburetorless]

The throttle rod has a flat spot that contacts a spring-loaded cylindrical piston that carries a tiny 0-ring. When you open the throttle, the piston is forced forward which pushes a small amount of fuel into the carb intake. These carbs seem to fail after extended use because the o-ring degrades and the piston scuffs the bore that it slides in. If the bore is scuffed, then a new o-ring will soon also fail. Do a search on "carbitooter" and get the whole story on this issue.

I took the carb apart looking for the piston, but I don't think I found it. There is a rod with sort of see-saw fork on it that has a spring under it, the fork raises and lower a needle valve. This is all held in place by a small screw.

Am I looking in the right place for the piston?

Also, once I find it; Should I take it out and fill the hole with apoxy like the thread on 200T suggests?

Something else I noticed while looking at the other things that were suggested; I took the spark muffler off to check the piston, then I sprayed some carb cleaner in there and pulled the start cord a little to move the piston through it's stroke. There were some bubbles during the compression stroke.

Does this mean I need to do a ring job on it, or is this normal leakage?

 

[ZeroJunk]

I'm not sure your carb even has one since the IPL I looked at doesn't show a carb with a primer pump, but if it does, read this thread to find where it is and what to do.

http://www.arboristsite.com/chainsaw/145024.htm

 

[Carburetorless]

I'm not sure your carb even has one since the IPL I looked at doesn't show a carb with a primer pump, but if it does, read this thread to find where it is and what to do.

http://www.arboristsite.com/chainsaw/145024.htm

My primer pump isn't on the carb it's self, it's separate and sends fuel to the carb by means of a rubber tube.

Where did my last post go?

 

[Carburetorless]

Update: I decided to tear this saw apart, when I took the starter recoil cover off I noticed a tube that wasn't connected to anything.

After removing the pickup coil I noticed there is a nipple on the black plastic whatchamacallit that fits over the back of the carb. I fed the hose up through the square hole in the case and connected it to the nipple.

Now the saw starts much better, and after some fine tuning runs much better. The gasket that goes between the carb and the intake is not in great shape. I'm thinking a new gasket and the saw will run great.

 

[Carburetorless]

I think I've found the problem

I put a new manifold gasket on the saw, but there was little if any change.

Next I ran the saw at different angles to see if there was any difference in how it ran. When I ran the saw level it would run pretty good, unless I moved it around a lot, then it would run pretty good most of the time, but sometimes it would bog a little.

Then I ran the saw with the bar pointed up, and the saw ran great.

Finally I ran the saw with the bar pointed down, and it bogged out every time. When I would point the bar up the saw would smooth out and run great, as soon as I pointed it back down it would start to bog out again.

So I'm thinking it's a crack in the fuel line towards the back of the tank where it exits the tank. When the saw is pointed upward fuel covers the crack so it draws fuel just fine. When the saw if pointed downward the crack is exposed and sucks air which leans the saw out causing it to bog.

I haven't removed the hose to check, but I pretty sure this is the problem.

 

[pgg]

fuel hoses are first to check, they'll bog the saw rich then next instant lean, and the tankbreather on those 192T's has only tiny pinpricks that clog solid with dust, leave's the engine fighting a vacuum, also if the saw drops down it's starter cord too easy then shagged compression, and the most insidious of all is an invisibly erratic flywheel that plays hell with the performance and usually sends the owner off chasing dead-ends on symptoms you'd swear had nothing to do with electrics

 

[Carburetorless]

if the saw drops down it's starter cord too easy then shagged compression

By "drops down it's starter cord too easy" you mean hold the saw by the starter cord and see if the weight of the saw cranks the saw over?

That's something I hadn't thought to check; Thanks for the tip.

O.K. I did the cord drop thing; It took about 6 seconds for the engine to turn over with all the saw's weight hanging on the starter cord, then about 4 or 5 more seconds for it to drop another notch/rotation.

I guess for an older saw that's pretty good.

 

[jus2fat]

By "drops down it's starter cord too easy" you mean hold the saw by the starter cord and see if the weight of the saw cranks the saw over?
That's something I hadn't thought to check; Thanks for the tip.

That's simply a "shade tree mechanic" way of checking the compression.

Best to buy a compression gauge..BUT..this little experiment should give you a general idea.

J2F

 

[Carburetorless]

Not the fule lines

I took the saw apart to check the fuel lines, they are great shape.

While I had it apart I noticed that the rubber intake manifold wasn't seated completely and there was a good sized gap on the backside of it. I removed it from the trigger housing/handle, removed the plastic cover that snaps down over the bottom of the manifold, and reseated it over the intake.

After reassembling the saw I fueled it up, pulled the starter cord two or three times and the saw fired up and ran great in all positions. It ran like a new saw.

The only thing I didn't like was that it was idling a little faster than I wanted, so I started adjusting the idle and Low speed screws, then all of a sudden the saw starts bogging again, but worse than before, and now matter how I adjust the screws it won't run right.

Only now though it's blowing fuel back through the carburetor; Could this have something to do with the pickup coil setting, or is it something else?

 

[jus2fat]

Have you checked the muffler screen to see if it's clogged up..??

When I see 'spit-back' from the carburetor..that's the first place I look.

J2F

 

[Carburetorless]

Have you checked the muffler screen to see if it's clogged up..??

When I see 'spit-back' from the carburetor..that's the first place I look.

J2F

Yes. The only problem, if it is a problem, is that there is no screen material in the muffler under the little flange with the screw in it. What mesh size screen does it use?


I rechecked the carb settings, and it seems that I accidentally adjusted the High speed screw instead of the low speed screw. :frown: Someone must have turned it too far and broke the stop, so instead of stopping there's just a click when it goes past 3/4 turn.

After setting the high speed screw back to it's proper position and adjusting the Low speed screw the saw is back to running like new again.

It was the rubber intake manifold that was causing most of the problem from the get go, aside from the loose fuel line that was hidden by the pick up coil.

And wouldn't you know it, now that the saw is running good it's pouring down rain outside. lol

 

[jus2fat]

Yes. The only problem, if it is a problem, is that there is no screen material in the muffler under the little flange with the screw in it. What mesh size screen does it use?
After setting the high speed screw back to it's proper position and adjusting the Low speed screw the saw is back to running like new again.
And wouldn't you know it, now that the saw is running good it's pouring down rain outside. lol

Really glad you got the saw running again after re-adjusting the carb.

As for the muffler screen..leave it out.

Rain sucks...but better than snow..!!

(I really think you will like this little saw...I sure do mine..!!)

J2F