Outboard motor questions?

Question

Ok i have a 1995 3cyl 2 stroke mercury. My problem is that when i run the motor between 3000 rpm and 4250 rpm, the rpm's will drop to 3K then back to orignal rpm. It will keep going in and out like this every 30 seconds or so, it idles just fine. If I go any higher between 4300 to wide open, it runs steady. Ive replaced the inline fuel filter and the fuel water separator, installed new plugs. Does anyone think that this sounds like a clogged jet, fuel pump problem, or ignition. Im leaning more towards a clogged jet or its sucking air into the fuel lines somewhere. What do you guys think

Answer 1

I believe that you have an ignition problem.The fact that the engine seems to operate fine at low or idle speeds could be that you are really only running on two cylinders,at mid range the ignition is miss firing,and at WOT the ignition is over coming the fault.

   The first thing to check is are the spark plugs all firing and or are they fouled in any way.

   Run the engine at low RPM's for a couple of minutes then remove the plugs.Note which cylinder that you remove them from and check to see if any are wet/damp.If one is. switch it with a plug from one of the cylinders and repeat the first step.If the same cylinder is wet then you have a ignition problem,but if the first plug that was wet still is then replace the spark plug.

Answer 2

It could be an air leak in the fuel line, or maybe a clogged vent for the fuel tank. I would think the fuel pump might be a concern. Try pumping the fuel bulb while running in the problem rpm and see if that clears it up. Also check the bulb and make sure it is not collapsing on you. The bulb has a check valve in it that also can go bad which can cause problems.

Answer 3

do what mark said also you can take the cap off of the gas tank and see if it does the same thing, if not it is prob a clogged jet , could be fuel pump i doubt it is an ignition problem, but look at your coils and spark wires make sure there is not any cracks or swelling..good luck....