PTO crank seals causing high idle??? - Snowmobile Forum: Your #1 Snowmobile Forum
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post #1 of 6 (permalink) Old 02-02-2008, 08:17 AM Thread Starter
Leonard Evans Body Shop
 
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PTO crank seals causing high idle???

Please help me to understand this, I see alot of people saying a crank seal would also cause high idle, not that that is my problem, I just want to understand this, as obvoiusly its not like an automotive engine, I just do not see how that could affect the idle

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post #2 of 6 (permalink) Old 02-02-2008, 08:40 AM
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when you have an air leak it causes a lean mixture in the cylinder which in turn will make it rev too high at idle. If you have an air leak you should be able to tell by your jetting.

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post #3 of 6 (permalink) Old 02-02-2008, 08:48 AM
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Leaking crank seals cause the air/fuel mixture to LEAN out, as the mixture leans out the engine revs higher because the mixture is burning so efficiently. However since the mixture is buring so efficiently it also burns very HOT and at higher RPMs the engine can't sustain the extra heat and the piston will likely seize(usually on the exhaust side). The reason the mixture will lean out is because the leaking seal will let more air into the mixture after its forced into the crankcase. Try running your lawnmower or car out of gas and you will hear the RPM go up and peek then die. Same thing with your engine except there is still enough fuel in the mixture to keep it running.

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post #4 of 6 (permalink) Old 02-03-2008, 03:40 AM
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Three ways to tell if you are running lean.
1. Popping at the exhaust
2. Plug electrode color is gray or white.
3. The engine suddenly has a lot of pep that was never there before. (they always run their best just before failure)

Either one is a good indicator, although, # 1 usually means that the damage has already progressed to the point of needing repair immediatly.
To test for a air leak, you can use starting fluid that you spray around the crank seals, the carb mounting flanges (boots) and the head and base gaskets. This is done with the engine running and if the rpms go up, you have an air leak. Do not run the engine any longer, but get it fixed right away.

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post #5 of 6 (permalink) Old 02-03-2008, 08:55 AM Thread Starter
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excellent explaination, I dont think thats the problem, good thing to watch for tho, I just have to get out there and figure it out, was just curious as to what this meant, but will be the first thing I will check as it is so easy, I do see some fuel seeping from one of the carbs where the fuel line connects on the side of the carb body, it is like a little elbow block that the line hooks to, not sure what to do about that or if I will need another carb body

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post #6 of 6 (permalink) Old 02-03-2008, 03:05 PM Thread Starter
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I think it is my cable as I have checked everything,, cleaned the carbs, sprayed brake kleen all around and no difference, but it appears that It seems to could possible be over oiling, im buying a new cable from DennisKirk - Production Website Home page,

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