Engine loping at WOT

[scruffy_fish]

Took the boat out today and at WOT engine started to slow and drop back and then pick up again. I trimed it back and it ran fine until I brought it back to WOT. Trolled around for an hour or so and trolling speed was great. On the way in, same reaction at WOT, loping until I bring it back to a slower speed. <br />I do have last years gas still in the tank that was treated with stabil. (Engine 50HP '84 Mariner 4 cyl). Rebuilt carbs just before winter, first time out this year. <br />Any help would be apperciated.

 

[WillyBWright]

Re: Engine loping at WOT

Could be carbs. Could also be losing spark. There are two kinds of windings in the Stator which makes the electricity for your ignition. High Speed and Low Speed windings. If your High Speed windings are bad (EXTREMELY common on old black stators), then you start losing spark above 3/4 throttle. Connect a timing light and run the motor on the water. If the spark goes away, so will the flashing. If this is the case, it could also be the switchbox. It combines the low and high speed windings internally and if the high speed circuitry is bad it'll act just the same as bad high speed windings. That's pretty common as well.

 

[scruffy_fish]

Re: Engine loping at WOT

Thanks,WBW.<br />I have narrowed it down to possibly restricted fuel flow, because I went to a smaller size fuel line. When I rebuilt the carbs last winter I had an air leak which held down my top end so I went down a size on the fuel line, to get a tighter fit. Maybe not such a good idea. <br />Does any one know the correct size fuel line for this motor?

 

[bluegillspeed]

Re: Engine loping at WOT

a couple years back I rebuilt the carbs on my merc 500 50 hp, not much different from your engine I think. After the rebuild the timing advancement was off. The engine ran fine at idle ans slow speed but when I tried to accelerate there was no power. I fixed this by readjusting the amounnt the timing would advace with the throuttle. If your engine is similar enough to mine there should be two screws on the distrubitor that control the timing advancement. I woule recoment doing this on the water if you cant manually put a load on the engine.