Most common air leak areas on a 372?

[Mattyo]

The clutch holds the bushing in and aids the seal. So no this is not a problem.

 

[Mattyo]

At this point I'd lean toward the carb being the issue ....or the issue being at some point during fminiuel delivery....or even bad coil. So before you go crazy and take the top end off...I'd throw some other new parts at it.

How about tuning...how much have you messed with the carb tuning?

Mweba on YouTube has a great video on tuning carbs.

You have a heated handle saw which is a very desirable unit. Worth throwing some bucks at for sure.

 

[Mattyo]

btw....yes use brake cleaner but use it with the top cover off. Much easier to see where u r squirting it.

To me the idle sounds low...but thats all. If the saw has 2 idle spots then in the past I've had that be either carb or coil. ..not an air leak.

 

[kneedeepinsaws]

I checked my kit and no o ring i have is that thin...

Saw has a new unlim coil. Gonna re assemble tomorrow and try again i suppose...
Probably carb to boot connection, caused my grief before. No matter how rich i set L and adjust the Idle, it was surging...

 

[Mattyo]

If the coil is new id put a fresh hd12b carb in there. Fresh new carbs fix a lot of odd issues.

Those are proprietary o rings. They are not available in o ring supply houses. I've checked.

That said I've put a ton of 372s together with out that o ring. Never knew it was there lol. That's why I had to issue that apology vid on my channel. Now I use it for sure. In the meantime you can just pack it with grease and it'll seal well enough and be retrievable.

 

[BuckthornBonnie]

Kit and clean that carb even if you’re purchasing a new one.

Check the fuel system again (new oem plug and filter?) and make sure a line isn’t pinched somewhere.

To your original question-
As said above, bad bearings taking out seals or cases, base gaskets or poor attempts at gasket deletes. This series has a very simple fuel/impulse line that I actually like (mainly into Stihls, so I see tons of the molded lines cracked in hidden crevices), but it still can fail.

 

[kneedeepinsaws]

It has a new walbro branded carb.

tonight im going to check the fuel line and filter for a leak and or pinch and pull the vent and clean it as well.
If it was bad bearings the seals wouldnt hold right? Cause the pressure test passed?

i can find no play in the crank, but ill check again on a full 360 rotation.

thanks again!

 

[Mattyo]

It has new carb...OK. good.

Did it hold pressure on rotation of the crank during the pressure test?

How about vac?

 

[kneedeepinsaws]

It has new carb...OK. good.

Did it hold pressure on rotation of the crank during the pressure test?

How about vac?

That i do not know... i will check that as well when i am home.

 

[Stump Shot]

It is very common/easy to over tighten the carburetor mounting screws on a 372, causing the plastic mount to pucker and warp causing an air leak at the end of the manifold boot.

 

[kneedeepinsaws]

It is very common/easy to over tighten the carburetor mounting screws on a 372, causing the plastic mount to pucker and warp causing an air leak at the end of the manifold boot.

I am using a hutzl farmertech aluminum one. Ot does look tho like there should be another gasket of rubber or cork between the two tho... bottoms out way to easy

 

[Stump Shot]

I am using a hutzl farmertech aluminum one. Ot does look tho like there should be another gasket of rubber or cork between the two tho... bottoms out way to easy

Never tried one, couldn't really say.

 

[Mattyo]

I like the am ones....they are stiffer and less likely to bend than the oem ones. This is one of those rare am parts that they really made better imho

 

[kneedeepinsaws]

Alright, just finished dikkin around in the garage after a long long day at work.

i took off the oil Pump and chainbrake assembly to expose the clutch side seal. I cleaned it out good and proper to make sure i didnt get a piece of wood fiber in there for the o ring to not seal on properly. put the oil pump back on with it nice and clean, put the chainbrake assembly back together (that was not fun) and re assembled the worm gear, bearing for clutch and drum etc.
did another vac test right after, 10” Hg for ten minutes. Rotated the crank many times by hand, pressure dropped then increased with rotation but would stay at 10 given the right position.
Did a pressure test at 7psi, rotated crank, did full revolutions multiple times, same as negative pressure test. Held at 7psi for ten minutes.

thats where im at now, so i think i can rule out bottom end seals and top end leaks as an issue..

Next going to fuel system, gonna pull the tank prob tomorrow when i have a fresh mind and pull the fuel line, vent and test both. Probably clean out the vent and do a pressure vac test on the fuel line... when i put it back i gotta make sure its not pinched, any pointers there?

after that im gonna focus on the carb and do the FSM tests, if it passes ill then move on to the carb mount. I bought 5 of these a long time ago, they seem pretty decent. To be safe i think im gonna make a gasket or o ring or piece of cork gasket to give it a more proud sealing surface. Any thoughts on that?


Once again this is all very good help, and im quite excited to get all of your opinions and tips especially the veterans here.

 

[Mattyo]

Ok...so for now id agree to not worry about bottom end. Do you have any other carbs or coils you can swap out?

Pull the top cover off and run it ....then use the brake cleaner around the base and see if there is a specific spot that kills the motor. Doesn't need tons of cleaner to kill when there is a leak.

If you are using oem line just empty the gas out of the tank and check the line for kinks or being tangled.

Look where the fuel line comes through the tank up to the carb base and make sure that there is enough slack there.

You can use your mitivac to check the fuel line by pulling it off the carb and applying a vacuum to the line....does it suck up fuel? Don't get the fuel in the mitivac BTW.

Is the muffler spark screen plugged?

New spark plug?

 

[MERR6267]

I've had coil problems cause similar trouble recently. My MMWS 346 would not idle at all after it warmed up. I swapped carbs, pressure tested, fuel line tested, etc. Finally I swapped coils from my 353 and it's all good.

I burned the top end on my brother's 61, did a top end swap to a 272 and only after a lot of messing around did I realize the whole trouble was caused by a bad ignition. The saw would act really rich and "4 stroke" at 7-10k rpm, then if I'd lean it out it would sound like it was 4 stroking at about 13k. Sounds good, eh? No, it was super lean, but the ignition was just strong enough to light it up to 13k and then it would 4 stroke because the ignition couldn't light a full proper mixture. If fattened it up at all it would fall on its face. With only a coil swap it came back to normal tuning. The H needle was able to fatten up over 1/2 turn to properly tune.

My BIL has a 395 that would hunt like crazy at idle and tuning would cause high and low speed, stalling, etc. We found a thin spot on the high voltage lead that was grounding against the cylinder fin. At full throttle it vibrated at a frequency that it 'usually' didn't cause trouble.
We taped it up and moved it away from he cylinder and all came back to normal.

Good luck.

 

[kneedeepinsaws]

I have the oem coil i can put back in if the shenanigans continue. However the coil that is in there now has maybe 1 hour of runtime

still gotta go over the things i mentioned in the last post. But hopefully i get home a half decent time today to do some work on the saw. Going in for a root canal right now then right to work.

 

[kneedeepinsaws]

I've had coil problems cause similar trouble recently. My MMWS 346 would not idle at all after it warmed up. I swapped carbs, pressure tested, fuel line tested, etc. Finally I swapped coils from my 353 and it's all good.

I burned the top end on my brother's 61, did a top end swap to a 272 and only after a lot of messing around did I realize the whole trouble was caused by a bad ignition. The saw would act really rich and "4 stroke" at 7-10k rpm, then if I'd lean it out it would sound like it was 4 stroking at about 13k. Sounds good, eh? No, it was super lean, but the ignition was just strong enough to light it up to 13k and then it would 4 stroke because the ignition couldn't light a full proper mixture. If fattened it up at all it would fall on its face. With only a coil swap it came back to normal tuning. The H needle was able to fatten up over 1/2 turn to properly tune.

My BIL has a 395 that would hunt like crazy at idle and tuning would cause high and low speed, stalling, etc. We found a thin spot on the high voltage lead that was grounding against the cylinder fin. At full throttle it vibrated at a frequency that it 'usually' didn't cause trouble.
We taped it up and moved it away from he cylinder and all came back to normal.

Good luck.

Good info, thank you, there is a large part the ignition plays in tuning it would seem
I went thru two coils so far now with this wandering idle and crappy tuning... i however did keep the spark plug wire and just swapped the coil pack. The original wire was of a better quality and fit better.

 

[trooney]

Keep on chuggin man!! You'll get it eventually!! You'll be a hell of alot wiser!!!

 

[Mattyo]

I've had a few where I've swapped 2 or 3 coils before it ran right...very frustrating.

No more am coils for me....only oem for sure.