engine cutting out

[tburn]

1984 Exciter 350 Mercruiser, Just bought it less than a month ago and ran 4 or 5 times and it ran great. Took it out the other day and it started falling on its face when I would get up on plane. I went through the fuel system, carb had no problems,filters are good,tank was clean and no water anywhere. I did find some crap in the screen on the tank fitting and thought that would be the fix,took it out today ran great for about 5 minutes then started doing the same thing again. It only seems to die out when you get into the higher RPMs almost like its losing spark but, I checked (visually) all the electronics and all that seems fine too. It actually has stalled a few times up on plane, coast to a stop touch the key fires right up like nothing is wrong. So it leads me to believe it has to be spark. The only thing I found was some rust on the pick up that the rotor spins through so I cleaned that up and still have the problem. Could it be the coil or maybe fuel pump? Please help Thanks

 

[Jimway]

Hey T, does your set up have a fuel filter inside the carb at the fuel inlet to carb fitting? What kind of fuel pressure are you seeing at idle, and at 3500 rpm? At what rpm does the problem happen?

 

[tburn]

Yes it does have the filter with the check valve built into it in the carb. As for fuel pressures I have no way to check those. It seems to break down as you try to go up on plane, it will get up and go for a while then it starts surging a little and then seems like it just shuts off then fires right back up and runs fine until you do it all over again. It never really runs rough like a fuel problem though. If I pull out of the throttle it will run fine down low.

 

[Jimway]

Hey T, if I were able to take a look at the boat today, I would hook up a fuel pressure gauge at the carb and also hook up an inductive timing light to number 1 cylinder. I would splash the boat and try a quick run to simulate the problem you are having. A fuel pressure, or timing/ ignition problem, if present would be easy to see, like either low fuel pressure, or the ignition cutting out.

 

[tburn]

I'll check it out some more and let you know what I find. Thanks for your input.

 

[wca_tim]

try running it without the gas cap on once... could be tank vent plugged. also sometimes water / ethanol in the tank can do something similar... by plugging up the fuel water separator (assuming you have one) most of the way. in either case, it'll flow enough to let you run until you start going faster and use more fuel, then the pump starves, cavities and it dies...