89 yamaha f9.9 fouling plugs. To much idling?

[Jasonscott]

I have an 89 four stroke yamaha outboard that runs perfect until I troll with it for a couple of hours. Its on a 17' reinell and the fishing I use it for requires a slow troll. (idle) Is it normal for these to foul plugs if used too long at idle or could I lean the idle mixture up a bit to help. Im using the factory recommended plugs, maybe a step hotter? I realize this motor is a little large for what im doing but I dont have the coin to invest in anything else. I have a repair manual i acquired on cd, but its pretty vague in carburetor adjustments. There is only one screw on the carb that is adjustable (besides the idle speed screw) would this be my idle mix adjustment and would in or clockwise lean it? Thanks for any suggestions.

 

[rodbolt]

Re: 89 yamaha f9.9 fouling plugs. To much idling?

if the fuel system is clean and the piston rings are sealing correctly then set the pilot air screw at 3 turns out from lightly seated and the engine idle speed at 850 RPM in gear and the hull moving unrestrained.
if it still fouls plugs then most likly a ring seal issue.
do a leak down test.
now here is a trick.
with most kicker brackets and the engine tilted full down sometimes older rigs will oil foul due to excessive oil puddling behind the piston.
tilt the engine so the cylinders are actually higher on the spark plug end then the crankshaft end.
make sure the water intakes are still submerged.