b90 johnson 115 idle trouble

" Just bought this motor so ha

" Just bought this motor so have no history. It idles rough and feels like its only running on two cylinders up to about 1/4 throttle, then it takes off and runs fine. As I come off the throttle I can feel exactly when I lose the two cylinders again. Runs great from around 2500rpm and up. Seems to have good spark to all cylinders in my backyard test. What should I check next? Thanks "

"Kenny.... From what you'v

"Kenny.... From what you've said, and assuming that you have even compression of approx 100 lbs on all cylinders, and that the spark on all cylinders will jump a 7/16" gap with a strong blue flame..... what you are describing is a case of fouled carburetors. Fuel is not flowing through the small slow speed passageways and jets which is resulting in your engine running lean on whatever cylinders are involved. When you hit a certain throttle point, the intermetediate and/or high speed jets become involved, allowing fuel to flow normally. Look at the lower sides of the carbs (the float chambers). There will be a screw at the bottom sides. Remove those screws and inspect the back of them. If they're gummed, fouled, varnished, you can pretty well count on that carb being fouled, and it will require cleaning. You may have other problems but this is the most likely cause. If when running at a slow rpm and the engine is missing, running rough, etc, engage the choke/primer momentarily which will force fuel through the carb(s) even if they're fouled. If the rpms pick up slightly when you do that, obviously the carb(s) are at fault.

Joe "