1987 Mercury Motor Not running right Please HELP

[taxidermist144]

I have a 1987 Mercury motor, 35hp. It started fowling out a plug once in a while. maybe once in two to three years. I thought it was the fuel mix, change the plugs and it was okay.(Using NKG plugs) But it has gotten progressively worse. Setting in the yard idleing it runs fine, give it a little gas and you can hear a plug missfire once in a while. Put it in the water it will run fine until you throttle up to full throttle or next to full throttle. When it starts missfireing I can back out of the throttle and the plug starts fireing again and I regain power. I put the boat in a boat shop for repairs and they thought it was the trottle valve. But they rebuilt the throttle valve and it still does the same thing. If you have any suggestions I really need to know what to do. I am lost and I think they are too. Thank You taxidermist144
The motor is a 35hp twin cylinder, I run NKG plugs, I have used several kinds of oil mixes but the boat shop tells me they are using mercury mix in their gas. I also use 93 octain. The motor is oil injected but the oil injection system has been disconected.

 

[Paul DuLaney]

Re: 1987 Mercury Motor Not running right Please HELP

taxidermist144,What size is your motor and are you running champion or ngk plugs. In my older inlines I had bettr results with ngk than I did with champion as the latter would fowl out very easy.

 

[achris]

Re: 1987 Mercury Motor Not running right Please HELP

As well as asking what engine you have (horsepower), I would also ask what brand of 2 stroke oil you're using...

I've had engines that don't like a particular brand, but runn perfectly on other brands...

Chris...........