MS192T acting up - doesnt drop to idle immediately

WolfpactVI · Feb 5, 2013

Hello everyone,

I have a Stihl MS192TC that is acting up. Had someone from the forums help me tune it (thanks hoeyrd2110), and it revs and idles fine. However, coming off full throttle, it's almost as if the throttle is sticking. It doesnt drop immediately back to idle. Seems to stay at full throttle for a split second, then slowly drop back down to idle. If my memory is correct, it doesnt do it all the time, but a lot of it. I dont have the saw with me at the moment so I cant say for sure whether or not it happens every time.

We did pull the carb off and take it apart. Looked like new, no crud or corrosion that we could see. The screen in the carb was perfectly clean. However, we did notice when blowing air through the brass tubes that air seemed to be coming out around a little (maybe 1/4" diameter) white-ish plastic plug in a hole in the aluminum block of the carb. Wish I had taken a pic. I'll try to do so tonight. It's on the side of the carb opposite the diaphram.

So, the questions: What could be causing the slow return to idle? Air leak? That plastic plug in the carb? Could something be sticking? If so, what should I check?

Thanks!

- Justin

watsonr · Feb 5, 2013

WolfpactVI said:
Hello everyone,

I have a Stihl MS192TC that is acting up. Had someone from the forums help me tune it (thanks hoeyrd2110), and it revs and idles fine. However, coming off full throttle, it's almost as if the throttle is sticking. It doesnt drop immediately back to idle. Seems to stay at full throttle for a split second, then slowly drop back down to idle. If my memory is correct, it doesnt do it all the time, but a lot of it. I dont have the saw with me at the moment so I cant say for sure whether or not it happens every time.

We did pull the carb off and take it apart. Looked like new, no crud or corrosion that we could see. The screen in the carb was perfectly clean. However, we did notice when blowing air through the brass tubes that air seemed to be coming out around a little (maybe 1/4" diameter) white-ish plastic plug in a hole in the aluminum block of the carb. Wish I had taken a pic. I'll try to do so tonight. It's on the side of the carb opposite the diaphram.

So, the questions: What could be causing the slow return to idle? Air leak? That plastic plug in the carb? Could something be sticking? If so, what should I check?

Thanks!

- Justin

Those things you mentioned could cause it, also a sticking throttle rod, sticky trigger, spring on the carb may be getting weak. You could pressurize the carb body and test it with soapy water for a leak.

KenJax Tree · Feb 5, 2013

watsonr said:
Those things you mentioned could cause it, also a sticking throttle rod, sticky trigger, spring on the carb may be getting weak. You could pressurize the carb body and test it with soapy water for a leak.

You said sticky throttle rod:hmm3grin2orange:

nmurph · Feb 5, 2013

The first thing to check is that the L and H needles are set correctly. From there, assuming you don't have a sticky rod, you need to look for an air leak.

hoeyrd2110 · Feb 6, 2013

The only air leak I could find was the plastic plug on the carb to intake face for machining the high side needle. No sticky shafts or the like. Do the intake boots in these have any issues? I didn't take the saw down enough to take the boot off.

WolfpactVI · Feb 6, 2013

View attachment 277618 View attachment 277619

That little yellow-ish white-ish plug at the upper right of the carb is where there seemed to be an air leak. Is this normal?

Also, I checked this morning, no sticky throttle linkage, trigger or anything. The throttle plate in the carb was operating fine too. What spring am I looking to check? And we did tune it up, so all of the screws should be set right.

nmurph · Feb 6, 2013

Intake runner, fuel line, or crank seals...I would start by replacing the fuel line, and maybe you could check the intake at the same time. May sure you flex the boot to see if there are small cracks.

WolfpactVI · Feb 6, 2013

Is it normal for one of these items to be bad? I've had it only a few years (like 3 at the most) and only use maybe 20 times a year.

Trailtrimmer · Feb 6, 2013

WolfpactVI said:
Is it normal for one of these items to be bad? I've had it only a few years (like 3 at the most) and only use maybe 20 times a year.

Fuel lines are a maintenance item on a chainsaw, especially if you don't drain the alcohol blended gas from them before they sit for a while. A fuel line every 3 to 5 years is pretty typical.

Hddnis · Feb 6, 2013

Pine sap around the throttle will make it so they never return to idle. :msp_scared:

Starts out just sticking a little, then gets worse.

Mr. HE

fearofpavement · Feb 6, 2013

That fact that the saw DOES return to normal idle, albeit slowly, makes me think mechanical, not carb and air leak issues. You said the linkage isn't sticking or hung up but that is where I am laying my money. Unless you can get it to do it while observing and confirming the actual throttle plate position I think you need to revisit that area.

Check the linkages for cleanliness, make sure it didn't get bent and study any areas it passes through or near to make sure there is no rubbing. Sometimes even a fuel line can rub against the linkage and cause these symptoms. And if you have a cover off to see it isn't interfering, is it possible the cover is pushing something into the linkage only when installed? Keep checking.

If you had an air leak or defective fuel hose issue, my thinking is that it would cause more than a sluggish throttle response.

WolfpactVI · Feb 6, 2013

Hddnis said:
Pine sap around the throttle will make it so they never return to idle. :msp_scared:

Starts out just sticking a little, then gets worse.

Mr. HE

Sounds like the voice of experience. I hate sap. There are some evergreens around here (ugly, dirty, long needles, scaly bark, non-native, usually croak when they reach ~12" dia and 40' high) that are so full of sap they make my MS390 bog down faster than when cutting oak or elm, even with a freshly sharpened chain.

I'll pull the throttle linkage cover off and see how that looks. Wouldnt it be nice if that's all it was. Oh that I would be so lucky.

If that's ok, I'll check the rubber lines next. If they're ok, I guess I'll replace the carb and see if that fixes it. Hope I dont have to though, since they're about $80.

Thanks all for the suggestions. I'll keep you posted.

- J

Trailtrimmer · Feb 6, 2013

WolfpactVI said:
Sounds like the voice of experience. I hate sap. There are some evergreens around here (ugly, dirty, long needles, scaly bark, non-native, usually croak when they reach ~12" dia and 40' high) that are so full of sap they make my MS390 bog down faster than when cutting oak or elm, even with a freshly sharpened chain.

I'll pull the throttle linkage cover off and see how that looks. Wouldnt it be nice if that's all it was. Oh that I would be so lucky. If that's ok, I'll check the rubber lines next. If they're ok, I guess I'll replace the carb and see if that fixes it. Hope I dont have to though, since they're about $80.

Thanks all for the suggestions. I'll keep you posted.

- J

Just out of curiosity, are you running fresh gas, as in less than two months old? Did the saw sit for any amount of time unused while still full of fuel?

Slow return to idle can indeed be linked to incorrect tuning. A change in tuning typically comes from bad fuel, a carb that's gotten boogerd up from bad fuel or sitting fuel, a mix ratio change, temperature change or an air leak.

How warm was it last time you ran the saw? Did it act OK then?

hoeyrd2110 · Feb 6, 2013

he did mention he got the old bar bound up a little whiles ago, i don't have a vac tester at home but i did quick check the bearings and they were nice a snug. i think now it's gotta get torn down enough to check the boot. if i'm motivated(to put it back together) i may have a 335xpt you can use while figuring out the 192 if you want to do that. don't spend the $80 on the carb yet

his gas was fresh 93 when we tuned it, cause i cleaned out the tank and put my fuel in. carb was taken apart checked over cleaned out and reinstalled screws on factory setting then adjusted from there. when he was over it was probly 30 degree's out.

i'm scratching my alittle head over here as well. this is the first 192 i've done anything to other than sharpen the chain. the throttle linkage insidethe handle looks like no fun to me. nice little saw though. i'm dying to figure out what it is, or what i missed

Zombiechopper · Feb 6, 2013

nmurph said:
The first thing to check is that the L and H needles are set correctly. From there, assuming you don't have a sticky rod, you need to look for an air leak.

yup. biggest cause is L too lean. Start simple.

WolfpactVI · Feb 25, 2013

1137 120 3400

OK, finally had time to look at the 192T again. "Time" as in about 5 mins. Enough to look at the linkage, not enough to pull the fuel line. The throttle linkage is all nice and clean, all springs are nice and strong. Definitely nothing sticking on the throttle or carb. Only thing noticeably out of the ordinary was the black plastic plate behind the air filter that surrounds the carb (called the filter base in the parts list, part # 1137 120 3400). It has a short built-in tube in the back-top-center of it that fits over this snorkel coming out of the top of the carb. I have no idea what said snorkel does, but it has an o-ring on it, so presumably it needs to seal into the tube on the back of that filter base. The problem is, that tube is all broken up, and is in no way sealing to the snorkel thing on the carb. I found a new one on eBay, so when that arrives I'll put it in & then play with the L, LA, & H screws.

Out of curiosity, anyone know what the snorkel thing does? It's part of the plate that screws onto the top of the carb and holds the diaphragm on.

XSKIER · Feb 25, 2013

That "snorkel thing" is Intellicarb. It equalizes the pressure between the filter and metering diaphragm.

WolfpactVI · Feb 25, 2013

So if the intelicarb is leaking would that cause weird throttle response?

XSKIER · Feb 26, 2013

My best guess would be that a leaking Intellicarb would cause the opposite of your problem. The metering diaphragm would see atmospheric pressure, which is usually higher than inside the air filter. The higher pressure on the diaphragm would cause a more rich mixture 1/4 to 3/4 throttle opening. However, I would repair the Intellicarb before continuing to use the saw.

hoeyrd2110 · Feb 26, 2013

How's that 390 running?

I have a question about timing is there any chance the coil has a built in advance and its not coming down and resetting every full throttle run? Off the wall I know but worth a shot

MS192T acting up - doesnt drop to idle immediately

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