Compression Test - 120/90 - 30 PSI difference or 25% and ( Bad Idle)

[Greg2011]

I have a 1988 Johnson 40HP with the Vro2 oil pump.I have 2 questions: I checked the compression: •cylinder 1 has 120 PSI •and cylinder 2 has 90 PSI •a 30 PSI difference or 25%The engine starts, runs from 1500 RPM to 5500 like it was brand-new.The only problem is: it dies at idle when I set the idle from 800 to 1200 RPM with the engine in gear.Idles OK above 1500 RPM but too fast to get into a dock.The engine has about 800 engine hours on it. 1) How long do these engines normally last? (Piston and ring wear on block) = low compression!2) Is this 30 PSI the cause of the bad idle below 1500 RPM?Cleaned engine with Sea foamI checked the compression: • cylinder 1 has 115 PSI • and cylinder 2 has 85 PSI • a 30 PSI difference or 25%• Compression dropped 5 PSI after cleaning Thanks Greg

 

[racerone]

Not uncommon in the high revving 2 cylinder like yours.-----------------------Pull the cylinderhead and inspect, post picture of the cylinder and piston if you like..----Lucky you if it is just a blown head gasket ---------------------Motor may be repairable now ( new O/S piston ) or if you wait the trouble will be worse and it may be " new motor time "