[JohnBNTampa]

I am looking at a boat with an 86 225hp Yamaha Outboard. The motor was rebuilt 25 hours ago with a new crank, powerhead, etc. 5 cylinders are at 110 psi. One cylinder is at 140 psi. What would cause such a high compression rating in one cylinder?? Is this normal?? Thanks in advance for the reply!!null

[steve forsythe]

Sounds like to me .... 5 bad cylinders. Mine numbers on my 200 Merc were 140, 140, 135, 140, 140, 115. I am not sure what is 'high' and what isnt. But they should be the same.

[omctech]

Redo the compression test. If all 6 cylinders are not within 10 pounds of the highest reading, do not buy the boat.

[steve forsythe]

Agree!! If i had done my homework..i wouldnt have purchased either. $2500 later i have a great motor that runs fine...all 140psi.

[JohnBNTampa]

Thanks for the info guys! Could it be possible that only one cylinder was rebuilt, and not broken in yet?? I have taken the boat out, motor runs great. I don't understand what would cause such a high compression in only one cylinder.

[G DANE]

I guess you are right Johnny.You cant always count on what people says. If one cylinder has overheated or ran lean due to clocked carb or something else, they can have bored this cyl and put in a new piston. Ive seen this. If you are sure on mesuring, i would pass on it, if no good explanation is given. But its pretty low readings on the others.

[JohnBNTampa]

Went back over to the boat this afternoon. Mechanic said there was carbon buildup and to run some Decarbonizer through it. After doing so, all cylinders checked in at 110 psi. (Used a different guage as well) It seems all may be well. Any thoughts???