very odd 12a compression thing
 

ok i have a 81 12a that i built a few years ago. did a compression test on it with a mazda tester .... got good #'s back 90's on all... the thing is when the motors cold it fires up... when its hot you have to roll start it to get it to run... not far or fast may be 6 mph and pop the clutch verrom shes running good.... the odd thing is i am pushing compression OUT the front rotor intake ports. I pulled the intake off and put tape over the ports on the rear it sucks the tape in(normal...vacume) when you spin it with the key... on the front rotor ports it pushs the tape off.... blows it off the motor... and its pushing HARD... what would cause this? and y would i still have good compression?
Thanks. David


and im gonna open the motor soon to figure this out 4 sure

Dude, that is one WEIRD problem! Maybe there is some SERIOUS overlap in there:) Doubt it:)

I have no idea. I am trying to think of something but if all of your compression #'s are fine it is weird. They were fine on all 3 faces? Only thing I can think of is that a seal is gone. Maybe a side seal, so when it compresses it squirts past the seals out the intake.

resurrection. did you ever find out the cause of this problem? :)

Sideseals or corner seal something is letting the compression by.

yes, probably a side seal or corner seal or their corresponding springs. i built a Gen II 13B motor about 11 years ago and it would start fine when cold, but it would literally take up to 45 minutes before i could get it to restart when hot. another thing is it didn't rev past 5000+ RPM under load, but it felt great at low RPM. strange ...