Air leaks and crank seals.

[Boomer 87]

Hey all, just joined the site and hope to have a good experience here. I hate to hit you guys with my problems right off the bat. But im working on a poulan farm pro 375 that im having trouble with a suspected air leak. When the saw is layed pto side down it climbs 500+RPMs, when set upright it settles down. When set on the flywheel side theres no change. What do you guys think? Experience tells me crank seals but ive made that repair before and there was no change. Is there anything else im missing that could cause an air leak based off the saws position?

I should say ive rebuilt the carb and new fuel line and filter installed also. I own 8 of these saws so i kinda know the in and outs of these units. Any light anyone can shed would be appreciated.
Cody.

 

[merc_man]

Have you tried a vac/presure check

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[Boomer 87]

Im going to do that tomorrow, mostly wondered if anything besides crank seals could cause a leak only in certain postions.i would think if its a gasket leak, it should leak no matter the position.

 

[merc_man]

I would bet its a crank seal if it only acts up when you turn on its side.

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[Boomer 87]

I hope so it runs great and idles fine its just the rpm change pto side down.

Also i tached my hi side @9,250 rpms wot. Does that sound right? It still 4 strokes heavy at those rpms. Thats with bar and chain no load rpms

 

[merc_man]

If its four stroking at WOT your good. Id still presure and vac test before much running so you dont do any damage to it.

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[jb-chainsaws]

As others have said get a pressure/vac test done, then if you're struggling to give it a constant supply of low pressure air to find the leak or its a hard one to find as some are then change the seals and test again.

When you're testing make sure to rotate the crank, the gauge on the tester should fluctuate a bit as the saw is turned over but it shouldn't leak down to zero

 

[Mastermind]

I moved this to the saw forum to get more exposure.

 

[Boomer 87]

Thank you i came from AS its alittle different navigating here.

 

[Mastermind]

Thank you i came from AS its alittle different navigating here.

Welcome to opeforum sir.

 

[Whiskers]

If it's a small leak it also helps to have the saw stripped down to just the engine and case. Then you have access to all the leakage points.

 

[Fruecrue]

Not familiar with that saw, but...
Could the fuel line in the tank be restricted in that position?

 

[TJ the Chainsaw Mechanic]

Sounds like seals to me, if you tip the nose forward does the rpm drop? Metering lever set to high? Like others have said, do a pressure/vacuum test for sure...Cold and Hot. Sometimes seals will leak when the saw is hot and not when it's cold.

 

[Johnmn]

Just replaced fuel line on my 670 that acted similar but mine stumbled when on clutch side. It fixed my problem. Seals were replaced on my saw only 2 tanks before this issue came up so I didn't figure that was it

 

[Boomer 87]

Im gonna do a leak test after work. Ive put in new carb kit new fuel line and filter. Its gotta be seal leak

 

[Boomer 87]

I sprayed around on the saw also with carb spray, around cylinder gasket, intake manifold gasket, carb gasket. And didnt get any RPM fluctuations doing that. Running, the saw keeps a tune and idle speed fine and runs good WOT and doesnt lean out at WOT either. So time will tell ill keep posted later this evening after the leak test.

 

[2manyhounds]

Had a couple 200t's that it was a tore boot when that happened,,not sure if that model has a boot but something to think on.

 

[Boomer 87]

Ok so heres what i found. It had a pretty substantial leak both pressure and vacuum. So i removed the clutch and put a bead of grease on the pto side seal, the leak slowed but still existed. so removed flywheel more grease slowed more but still exsisted. Got out the windex and sprayed around.....
That is the intake manifold gasket thats bubbling. Lucikly i have all the nessacery parts to fix it on hand. Thanks to all who responded i do appreciate. Cody

 

[Al Smith]

I'm not familiar with the saw either .However as a general rule if the saw acts differently when tilted it normally would be a fuel line leak, torn boot or something like that .If it progressively appears to lean out with run time it most likely is a seal going bad .Usually it's the clutch side seal .

I know for example for years people blamed a faulty carb on Stihl 200t model but most times it was a bad seal caused by a worn crankshaft bearing .I'd imagine Stihl sold a million dollars worth of Zama C1Q carbs at 90 bucks a pop which didn't solve the problem .

I might add with all that said that to trouble shoot a saw over the internet is at best a guessing game .All ideas might have some merit though based on passed experiances .

 

[Boomer 87]

Going to do a tear down and repair today as i have to pull the jug to replace the manifold gasket. Does anyone put any sealer on gasket surfaces?, or around the O.D. of the crank seal? They dont from the factory, but maybe its good insurance.