1990 90hp Force missing at high rpm

[bassmasterdude]

Helping a friend with an issue missing at high rpm. Runs great at idle and lower rpm but when you get closer to wot it starts to miss. I put my timing light on each plug wire individually and noticed all 3 cyls. were missing intermittently. When you back off the throttle a little the miss will go away. I have changed the plugs, changed fuel filter, tried pumping the fuel bulb, etc. I am leaning towards rectifier, stator or trigger. I did pull each plug wire individually and all 3 reacted drastically so it seems it has to be something common to all 3 cyl. Anyone have more tests for me before we start throwing parts at it? He is taking the boat out tomorrow and is going to disconnect the two yellow wires off the rectifier to at least eliminate that so I won't know until tomorrow if that was it but I have my doubts.

 

[maxum247]

Re: 1990 90hp Force missing at high rpm

Lean carburetor adjustment, can cause the engine to misfire at high speed.

Low fuel pump pressure, has the fuel pump been rebuilt recently?

 

[bassmasterdude]

Re: 1990 90hp Force missing at high rpm

The pump has not been replaced but the issue I have is there is a smooth spark signal on my timing light until the rpm's get high and then you can see in the light that it is miss firing and it does this on all 3 cylinders. To address the fuel issue, before I found the spark problems while running the boat during the mis fire I manually pumped the fuel bulb and there was no difference in engine performance.

 

[fab9racing]

Re: 1990 90hp Force missing at high rpm

if it has a lean or rich condition and it misses it will still effect the timing light it is cheaper to try and fatten it up just a bit than replace all the electronics, does it run like this ------------------------da------------------------da------------------------da or like this ------------------------dadadadadadad---dada---dada------dadada

 

[bassmasterdude]

Re: 1990 90hp Force missing at high rpm

I guess the best way to describe the miss is almost like partially choking it. Hard to explain. As you gradually increase the throttle (after it's on plane) it is intermittent but as you near wot it just blubbers. I am not comprehending how a lack of spark would be associated with a lean or rich issue? If it were the fuel pump wouldn't manually pumping up the fuel bulb temporarily cure the lean issue? I guess that is the way I have checked for weak pumps in the past. The other think I have done is retard the timing which has helped considerably but only because it is not getting the rpm up since the timing is retarded. This is a long shot but does anyone have any specs (ohm readings) for the trigger, stator etc? Thanks for the feed back guys.