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9.9 compression 90 and 85 psi Should I change the Head gasket? Will that increate my compression?

Well----I do not believe you will find a head gasket on that 9.9 model 2 stroke.-----What is the motor doing / not doing for you ??
 
It (white) smokes a lot from exhaust coming out a hole in the shaft about 4" below the bottom of the motor. I think this hole should have a plug in it but is missing. The hole has no threads inside. It also coughs under high idle and we think it is from an air leak from a gasket around the choke button. Got a gasket kit but haven't fixed that yet.
Inspected the cylinders and they are black but no sign of water.

Are you saying there is no head gasket for this model?
I just bought it last Saturday.
 
There is a water jacket gasket.----But no cylinder head that you can take off.-----Do not go installing plugs if you are not 100% sure of things on this motor.
 
Try opening the low speed screw to help with the coughing at High RPMs in neutral. Or it is normal because they do not like high Rpms in neutral. That is probably not a primer problem. put up a pic of the hole where the exhaust is coming out.
 
Exhaust hole is apparently there to compensate for the lower exhaust pressure during idle. At higher speeds the exhaust pressure is sufficient to overcome the hydrostatic pressure at the bottom of the motor.

Haven't checked coughing yet.
 
flyingscott said:
Try opening the low speed screw to help with the coughing at High RPMs in neutral. Or it is normal because they do not like high Rpms in neutral. That is probably not a primer problem. put up a pic of the hole where the exhaust is coming out.
Click to expand...
Primer had a split in the diaphragm replaced it and did not fix coughing - engine started coughing after it warmed up.- Were would I find the low speed screw?
 
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