Compression too low?? PLEASE HELP!!

[sunbird 18]

I am looking at purchasing a 1994 Yamaha 225 OX66 carbd engine to repower my boat with. The current owner say that a compression test shows 94 PSI across the board. To me, this sounds low, but I am not sure what a typical good running range is for this motor. Can anyone tell me if this is good, healthy compression for this motor??? Any reason to shy away from a commercially used engine with these compression numbers?
THANKS!!!!

 

[shes a keeper]

Re: Compression too low?? PLEASE HELP!!

Are you sure that the owner is doing the compression test properly ? The most important is that they are all equal . It does sound low i had a 1994 yam 150 and she had 120psi but i don`t know your motor. It sounds like they might of did the test incorrectly not sure

 

[EAVES]

Re: Compression too low?? PLEASE HELP!!

You need a mininum of 90psi to idle and 94psi is on the low side , however i have seen some older 2 strokes that were ideled around alot build up alot of carbon and would cause lower comp. you can run some Yamaha Ring Free through it and see if it comes up any but i would say buying the engine would all depend on the $$$$ that is being handed over for it. If you can just hone and re-ring it than it maybe worth buying but is really had to say

 

[JB]

Re: Compression too low?? PLEASE HELP!!

Guages, technique and conditions vary too much to get paranoid about psi. Decarb it, warm it up, have an experienced wrench test it with a different guage and they might all come in at 125psi. What is important is that they are uniform.

The chance of 6 cylinders all going bad by the same amount at the same time is less than zero.

That is a mechanically healthy engine.

 

[rodbolt]

Re: Compression too low?? PLEASE HELP!!

I agree with JB, as long as they are uniform your ok.
the 3.1L motors typically run in the 100-105 range but some replacement powerheads run in the 80 PSI range.
if your still worried have a leak down test run.
I would also be concerned about what maint has been done,water pump,t-stats,pressure control valve,VST maint,fuel pump replacements,O2 sensor cleaning and testing and so on.
the maint on modern outboards gets expensive but without they puke parts fairly rapidly.
doesnt matter who made it or 2 or 4 stroke. modern outboards must be correctly maintained or it can get expensive.
I looked just yesterday and Maytag aint on my shirt.

 

[rodbolt]

Re: Compression too low?? PLEASE HELP!!

sorry, hit the submit button early,,your engine cannot be a 1994 OX66 as they did not make it then.
the 225 was made in both the 2.6 and 3.1L versions for the 1994 production and both models were carbed.
the first year run of the 225 OX66 motors were 1997.
however if you can post the full model number we can aide in identifying what your planning to buy and advise from there.

 

[sunbird 18]

Re: Compression too low?? PLEASE HELP!!

sorry, hit the submit button early,,your engine cannot be a 1994 OX66 as they did not make it then.
the 225 was made in both the 2.6 and 3.1L versions for the 1994 production and both models were carbed.
the first year run of the 225 OX66 motors were 1997.
however if you can post the full model number we can aide in identifying what your planning to buy and advise from there.

I was pretty sure that it wasnt an OX66 just by looking at the cowl and the fact that the guy says that it was carbureted. (craigslist ad, talked to him on the phone) He isnt much of a gearhead. He just goes by what his mechanic tells him. He used the engine commercially on a charter boat for 3 years, unknown hours before then. He estimated adding around 1200 hours in those 3 years. He had it maintained every year with the regular things. With the potential hours on the engine, I wouldnt be surprised if the comp was low due to just having high hours. Guy says it runs perfect, just repowered with 4 strokes like the rest of the boats in his fleet for fuel economy reasons. I'll get you the model number shortly.