1996 40 HP Johnson fouling bottom spark plug

[ReellyKnotty]

Hi I have a 96 Johnson 40 HP on a 96 pontoon. I bought the boat from my parents who had the boat one year before i bought it from them. They bought the boat from the original owner! He always kept the boat inside and always had the dealer winterize and un winterize it. The boat ran great all last summer while my parents owned it, and great this summer until July 2011. We got caught in a bad storm and after the storm we were going to the dock and running WOT, the boat started to surge and miss out, almost like it was out of gas and finally died. the boat fired right up but would not run any faster than 10 MPH. I pulled the spark plugs and replaced them they were both wet and black. I also replaced the in line fuel filter which neither had been done since my Dad owned the boat. Took the boat back out ran fine for a couple hours then the same serging and miss, but the boat idles all day long and will run fine up to 10 MPH. I checked the plugs again and the same thing only this time it was the bottom plug that was fouled! The top has a little burn to it but not much, I bought new plugs again checked for fuel blockage, I have adjusted the two screws on the right side of the carbs (if looking at the engine from the back) and it did nothing.I have done everything I can think of, the boat is still doing the same as of 10/5/2011. The engine does not seem to be running rich it does smoke a little but nothing out of the ordinary. I have noticed that it seems like it is using more oil than it should, and when running on muffs the water coming out of the prop is very cloudy! The VRO seems to be working properly because the fuel in the clear fuel filter is the color of mixed fuel (blueish green). All fuel lines are clean, and I do not see any fuel leaking while the engin is running. The engine runs fine on the muffs and at idle but can not run wide open! I am useally pretty good at figuring stuff out but this has me stumped, any ideas or suggestions would be greatly appreciated thanks!

David

 

[Rick.]

Re: 1996 40 HP Johnson fouling bottom spark plug

A fuel leak will cause it to use more oil than normal, sometimes significantly more. Is there a chance it is over heating at high RPM? If it has an over heat it will cause it to go into SLOW mode but I can't remember what the RPM's drop to in SLOW. Best of luck. Rick.

 

[boobie]

Re: 1996 40 HP Johnson fouling bottom spark plug

Do a cyl drop test on it when running to see if it's firing on both cyls. Pull one plug wire off at a time with insulated pliers and see which cyl isn't firing.

 

[ReellyKnotty]

Re: 1996 40 HP Johnson fouling bottom spark plug

Thanks for the advice, my fuel connector from primer bulb to the VRO had part of the seal missing. Could this have been the problem?

 

[Haffiman]

Re: 1996 40 HP Johnson fouling bottom spark plug

Might have been sucking air on the fuel side making the oil mix ratio in the carbs too rich.
Short answer: Yes.