Chainsaw Repair

Sources of air leaks . . .

Seals around the crankshaft bearings on either the chain or flywheel side or both sides.

Carburetor intake rubber boot

Compression relief valve but I don't think the 5100s has one?

Impulse line if it has one.

- - - - - - -

The test involves blocking off the carburetor and muffler exits. Pump up the engine with 7 lbs of air pressure and check for leaks with soapy water? If you find the seals leaking at the crankshaft on either side, you have found the problem and no need to do the vacuum test.

And then draw 15" vacuum on the crankcase and see if it still has 10" vacuum after 30 seconds. The vacuum test is to check for bad seals on the crankshaft ends. The vacuum test will show the seals bad where the pressure test did not.

If it fails, you try some heavy oil on the seals and see if it changes the leak rate any.