Yamaha 70 troubles botom cyl?

[johnny whaler]

I have a 1994 Yamaha 70 Precision Blend outboard on my whaler. It seems to be having an issue with the bottom cylinder. I brought it to the dealer and they did a leakdown test. 1 and 2 were 90 and leaked down to 80. 3 was 90 and leaked down to 60. they then put some de-carbonizer in the jug and let it sit overnight. they blew it out and tersted it again and it was 90 down to 68 so 8 points higher. They told me to run Yamaha ring free in there and it should get better. I never saw an engine "get better" and I have my doubts.

While the engine is running in the bucket I pulled off plug wire 1 and it died, I pulled of plug wire 2 and it died. (one wire at a time) then when I pull of wire 3 very litle to no change in the sound of the engine. The spark looks good and they cleaned the carbs out.

This is one of the best rated Yamaha dealers around. Could they be misinf something simple like a weak power pack, leaking head gasket or maybe a bad #3 carb? Could this be the cause of posibly more carbon in the number 3 botom jug?

I'm not trying to second guess them or overthink but why just a problem in one cyl? Did anyone hear of running the ring free and running the boat hard and it "fixing" a problem like this? I just don't ant to play around and find out I have a bad piston or rings in June and miss 1/2 the season.

Any suggestions are appreciated. I'm ready to buy a new motor but I'm not sue if this is something simple they may have missed ot if it sounds like a scored cyl wall or something.

 

[Ray Neudecker]

Re: Yamaha 70 troubles botom cyl?

They sound like the voice of experience and could very well be right. Use good oil (Yamalube preferably)and the ring free to help clean up the carbon and the rings will likely reseat better.
The only other reasonable complete repair would be to tear down and rebuild.
Wally World oil is a no no.