Air Leaks


Well-Known Member
Local time
2:27 AM
Oct 2, 2021
An air leak can be one of the most frustrating issues that can be challenging on a CG engine.

If the tune is in any way erratic there’s a good chance an air leak is the reason.

On the outside it’s fairly straight forward running these down.

If it’s between the combustion and clutch shaft area inside.. not so easy to see it.
I guess a leak down pressure tester is in the cards for me. I would have found it sooner.

My leak is…was intermittent and not bad. Most times the engine ran perfect and other times behaved like a leak. It didn’t matter if the engine was hot or cold.

I had to split the case to change the crank out and found it. The case gasket was split right in the area where the oil passed. I must have damaged it putting it back together last time.

Upon splitting the case I found 2 stroke engine oil on the clutch shaft and spring. Clearly I had 2 stroke oil getting into that area.
I would find traces of oil on the bevel gear side and change the seal thinking it was a bad seal. The sprocket side not so obvious. Chain oil is in that area so it wasn’t obvious.


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