[boxermania]

calling911

Based on your posts and the good advice I gather that you are expecting things to change for the good, unfortunately it won't happen. On the other hand you do have a point based on the inconsistencies of your measurements and hopefully I can help you find your answer.

Compression Test

First the engine should be warm
Pull the relay for the fuel pump so as to not spray fuel into the cylinders
Open the throttle valve and lock it open
Check compression on all cylinders and record

With a syringe and a long piece of tubing, squirt 5 cc's of oil into each cylinder
Check compression on all cylinders and record.

Compare the two compression tests, if the values increase as I would expect there is blow by past the rings. The sources are many such as: worn rings, out of spec ring lands which allow the rings to "rock" as the piston moves, cylinder out of round, gummed rings and of course broken rings amongst others.

Small differences in compression between cylinders are not a good indicator of valve sealing, unless there is a badly burned or broken valve. Hence, the advent of the leak down test.

Leak down Test

This can be done following the compression test if the engine is still warm with each piston at TDC and not allowing the crank to rotate while doing the test. The readings will indicate leakage via one of three potential paths; the rings, the intake valve and the exhaust valve.

In order of the most likely problem I would go with exhaust valves (heat/air cooled engine), rings (mileage, gummed) and intake valve. In some extreme instances one could find a hole or crack on the piston (detonation or turbo lean out).

john_cramer’s rule for leak down; 4% good/10% marginal/30% teardown is an excellent starting point.

Last but not least, the smoke you are experiencing during deceleration, to read, engine vacuum is, as you suspected, excessive clearance on the valve guides or bad valve seals, albeit the original alloy of the valve guides didn't prove too durable.

So, in closing, the engine needs some attention and might make a good project if you have the inclination to go after the rebuild.

Best of luck and keep us posted.