compression problems

[akhiok_grizz]

I just recently bought a used 90 horse yamaha. Took it for a test drive and

my motor just died. I got it started and now it only runs on two plugs. Brought the boat home and pulled the spark plugs and the plug on the top was melted. I went and bought new plugs and a compression tester. The top cylinder has little compression but not enough for the compression tester and the other two have 6 to 8 pounds. What do I have to do to fix the problem.

 

[robert graham]

Re: compression problems

Well it don't sound good!, but maybe pull the head off the motor to inspect for damage, sounds like a lean fuel mixture caused by plugged carbs, overheated the pistons, rings may be stuck in grooves,damaged cylinder walls, etc. Check it out and maybe repair/replace power head. That's about the same motor as mine and I'm sorry to hear about your problems. Good luck and let us know what you find out.

 

[Mark42]

Re: compression problems

If there is no compression on the top cylinder and only 6 or 8 lbs on the other two, it sounds like the motor is toast. Like was said before, pull the cylinder head and inspect the pistons and cylinder walls for damage.

Is there oil in the oil tank?

 

[99yam40]

Re: compression problems

I find it hard to believe that the motor will run on two cylinders with only 6-8 lbs of compression in them and none in the 3rd.
Something does not sound right, maybe your tester is bad.