carbon fouled

[Berke]

Hi All, I Recently bought a boat with a Force 70HP 1992 engine. The engine had one damaged piston when I bougt it. So I had the engine rebuild and it ran fine for 6 hours. Yesterday it started to misfire and stalled a few minutes later. This happened after I ran the engine at 1600RPM for one hour. When I got home I checked the spark plugs and found that the lowerst spark was carbon fouled. I've cleaned the spark and the engine ran fine again. Does anyone have an idea why this could have happened? The information I've found is that the engine is running to rich, but I'm supprised that only one spark plug was carbon fouled. The oil/gas mixture is currently 1:25 (first 10 hours after the rebuild). Many thanks in advance.

 

[steelespike]

Re: carbon fouled

I assume you mean the breakin mix is 25:1 approximately 5.3 ozs per gallon.
approximately 1 gt to 6 gallons.
As for as fouling I've found in my limited experience that the lower cylinders tend to run a little wetter than the top.Also I don't know how many carbs are on the 70 but the bottom carb could be a little rich.Also the spark could be a little weak.
It seems that 1600 rpm is a pretty slow cruising speed 6 or 8 mph.Planing speed would be better unless you have specific instructions to stay below 2000 rpm. Most economical cruising speed is in the range just above planing up to about 2,000rpm higher.You'll have to test it out for the best rpm.

 

[Berke]

Re: carbon fouled

Thanks Steelspike. Yes, I meant the Breakin mix of 25:1. The 70HP has only one carb. 8 mph is the general speed limitation in Belgium... I will test if the spark is to weak.