89 gt150 low power

[Dholbrooks]

I'm new to outboards. I bought a 1990 17' stratos bass boat with a 89 gt150, previous owner said it wouldnt get on plane but we ran it on muffs and it sounded good Put it in water it doesnt idle well and throttle response is slugish and real weak took it home pulled all the plugs and ran compression test and all 6 cylinders only had between 59-61 psi. Im thinkig i have a sealing problem in the crankcase.

 

[racerone]

Sorry. crankcase compression / sealing has nothing to do with the compression in the cylinder.--------Some might argue that fact.

 

[Dholbrooks]

Sorry. crankcase compression / sealing has nothing to do with the compression in the cylinder.--------Some might argue that fact.

That sounds reasonable, it just seems odd that all six would be down that much and it even run. Like i said im new to outboard but have plenty of experience with diesel engines

 

[joereeves]

Sorry. crankcase compression / sealing has nothing to do with the compression in the cylinder.--------Some might argue that fact.

Total agreement with Racerone..... Compression exists only in any two cycle cylinder when the piston rings pass above the exhaust ports... rising upwards to TDC. It has nothing to do with "crankcase pressure"!

Note that compression is related to the speed with which the engine cranks over... a slow cranking engine cannot develop a proper compression reading. Crankcase pressure exists only to force the fuel mixture up and through to the intake ports. Don't get hung up in that mythology of quacks pertaining to crankcase pressure adding to and needed to create compression.

If the engine is cranking over normally, try a different gauge. If still a low reading, I suggest you remove the cylinder heads in order to inspect the head gaskets, the sealing surfaces of the head and block (crankcase), the pistons, and the cylinder walls.

Let us know what you find.