'89 yamaha 225 excel compression

[micel]

A friend of mine has a '89 225 yamaha that stalled while at sea although it would it would run on trailer.I informed him I had seen this before and that it usually meant that it dropped a cylinder.After convincing him that the easiest way to tell is to do a compression check and he agreed and the#1 was 100lbs,#2 was132 and the rest were close to 115lbs.I did check this with engine cold and dry.I told him he basically needed a rebuild.Since then his usual mechanic did another comp. test with engine warm(1/2hr running)and lubricated cylinders before checking compression and said engine is fine.The only reason I got involved was that I was planning on doing some 40 mile runs offshore with him. I told him I would buy a new engine b/c his was shot(he could not afford one).He now thinks that I just wanted a share in his boat and thinks I was trying to rip him off.Did I diagnose it right?Won't the lubricant falsely raise comp.,plus checking it warm?How good will the engine run or will it run at all with that much of a variance in compression? Much Thanks Michael

 

[yamamarinetech40]

Re: '89 yamaha 225 excel compression

Well, since the problem occured with engine running, I would say the compression would be same when problem happened as when he tested it as good...right? So probably wasn't problem, right? Did you open the throttle when you tested? Did you realize Yamaha builds different compressions between cylndrs. on purpose(from up to down, same across) on SOME engines? You probably shouldn't be just throwing that kind($$$) of advice around, especially to friends....sounds like carb cleaning to me...will spool up on hose with very little(drops) of fuel, takes a lot when loaded.

 

[ghind]

Re: '89 yamaha 225 excel compression

That compression difference isn't too bad considering the age of the motor. It could be improved by a simple decarb.

Any decent Yamaha mechanic should be able to fix this model motor.

As a backyard mechanic I'd start with checking the spark plug caps (resistance specifications), replacing the plugs, checking the fuel system for air leaks (it is a fuel system not an air system, air is bad), check/replace the low pressure fuel pumps.

Greg

 

[micel]

Re: '89 yamaha 225 excel compression

Thanks for input guys!I was just trying to help him and it upset me that he would disrespect me after saving him big $ on multiple engines over the years,plus the waste of my unappreciated time.I think he blew the engine since b/c he's been asking my opinion on new outboards,I'm not going to make same mistake twice!I have been taught with 2-strokes a 10% variance in compression is the cut off on a healthy engine and this one was 2.5X that.What is the maximum variance between cylinders to have a dependable engine?

 

[ghind]

Re: '89 yamaha 225 excel compression

All of the cylinders have substantial compression. A simple decarb may very well bring them all back to near new specifications. No need to be recommending a new motor.

There are plenty of things to look into but really now would be a good time to encourage him to find a skilled mechanic rather than giving advice which is really 50/50 at best.

There is plenty of posts on this forum about how to test the list of things I put above.

It is possible the motor is blown, who knows from what you've posted here. It is just as likely to be a couple of hundred dollars in parts to make this motor as good as new.