Compression questions

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Jun 17, 2009
Hi everyone!
I am the guy with the white smoke pouring out of exhaust thread questions.
I would be interested in your further thoughts:
Went for a ride, waiting one hour so motor just warm, compression guage showed 80psi on both, this with throttle closed.
Yes, I NOW know it should have been open, but its been some 20 years since I last did a comp test I just plain forgot.
I then pouring a teaspoon of motor oil in each spark plug hole and kick six times again, now comp. shot up to 120 both, throttle closed.
Can anything be interpreted from this? Please don't make me drive 40 miles round trip to borrow the comp guage again for throttle open test.
Bike starts first kick and really does run just fine. Some 12,000 miles ago since new pistons and rings, and valve guides and valves lapped, but all
head components from 1973.
Appreciate any comments
The compression readings you got are about what I would expect with closed throttle. They are saying both cylinders have even compression which is about all a compression test is going to tell you unless you have previous readings under the same conditions to compare them to. The rise in compression with oil is normal as filling the cylinder with a teaspoon of non-compressible liquid effectivly raises the compression ratio. Jim
I agree with Jim, 80psi with a closed throttle sounds ok, especially as they're both the same, also putting oil down there would increase the presure, that's to be expected. If you were only getting 40psi or so and then the pressure increased markedly with oil it could have pointed to piston/bore/rings problems but in that case it would be very unlikely for both cyls to have the same problems.
So, all sounds ok, still no nearer to solving your problem though!
Just a thought, I suppose it's not possible that there's something in the fuel? Have you used any fuel additive (Millers etc) and overdone it a bit, (or a squirt of diesel by mistake when filling up)!
Thanks for the compression comments, I think I am ok there based on what you have said!

And I believe I have solve the white smoke at start up issue.
As my center stand is remove, by choice, I now end a ride by putting the bike on the side stand but with a one inch block of wood under it to raise the
bike up to very close to upright. When I start it, I now very gently let it warm up holding the idle at 1200, no choke, for a minute then take off,
shifting at 3500 and riding very easily until the motor is fully warmed up. I believe I was stressing the motor and sucking oil up in to the combustion
chambers too early by goosing the throttle up to 4000 to early in warm up.
Anyway, no smoke anymore and all seems quite well!
Thank again for the comments
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