1989 70 HP 3-CYL One Plug fouling

[Jim Lloyd]

E70ELCE

Brand new plugs, the dirty one is the bottom cylinder (#3). Engine is spitting back through the carb on the dirty cylinder. My first thought was the thing is running super rich, but this is dry sooty carbon (like a Ficht) and if I give it a shot of carb cleaner into the throttle body, it picks up rpm. Am I dealing with a lean condition on the idle/slow speed circuit? Am I reading this plug right?

Compression is 130# on all three cylinders.

I swapped the top and bottom carbs and moved the problem to the top cylinder. It's definitely a carb issue, but this is a buddy's boat and I'm not digging into it w/o a service manual.

 

[James R]

Re: 1989 70 HP 3-CYL One Plug fouling

If the carbs have not been cleaned and rebuilt in the last two years then that's what's needed. If you want to ruin a good two stroke motor then keep shooting carb cleaner into it. When you do get the carbs cleaned and rebuilt be sure to use Stabil Marine in all your fuel.

 

[boobie]

Re: 1989 70 HP 3-CYL One Plug fouling

Edit.....

 

[Jim Lloyd]

Re: 1989 70 HP 3-CYL One Plug fouling

No worries on the carb cleaner, I gave it a couple of quick of shots at idle speed to see what happened to the rpms. This boat gets used year round, so fuel never has a chance to get old. It is E10, but fuel lines are all ethanol resistant and the carbs were overhauled last year. My bud said the condition came on suddenly. I'm thinking some trash worked its way into the carburetor and is the root of all this evil.

A carb overhaul will be forthcoming, I'm just trying to validate my diag. Does it make sense?

 

[boobie]

Re: 1989 70 HP 3-CYL One Plug fouling

Yes........ Especially since you switched carbs and the prob followed the carb.