Engine cutting out....

Ok, on a couple of occasions when running at WOT after about 1 minute at this setting the engine would start, what I think, backfiring and loosing power. At WOT I'm showing about 4k on the tach, which I know is relative.

As you know, I converted the distributor with the electronic box, replace the wires and plugs, etc...other than that, the 351 is completely stock.

If I back off slightly on the throttle, the problem disappears. This problem only exhibits itself at WOT.

I am thinking an ignition issue. Any thoughts on troubleshooting? I have a few months to think this over.

thanks

Yup, fuel delivery. Goes flat, lean pop, fix before fragging a piston.

Ok, I found the answer myself. Interesting.

From Wikipedia-

Improperly adjusted carburetors that create a lean condition during acceleration can cause the air fuel mixture to burn so slowly, that combustion is still taking place during the exhaust stroke, and even when the intake valve opens. The flame front can then travel up the intake and cause a backfire.

Beat me to it, but I thought a weak mixture would burn faster being more volatile due higher ratio of oxygen in the charge.

Tomski wrote: Beat me to it, but I thought a weak mixture would burn faster being more volatile due higher ratio of oxygen in the charge.

   Boat dr. has it right,but I'll expand on it cause I'm bored!Lean is harder to ignite to a piont.The fuel molecules are too far apart for the flame front to spread.If you lean it out too much,you'll actually have more unburnt fuel leaving the exhaust than if it were slightly rich.

The popping thru the intake can be caused by being lean(most common),and some timing issues will cause it.Also improper intake\exhaust tuning causes reversion(see previous post about exhaust valve being open while intake charge coming in-cam overlap).

Lean is mean.Too lean and MR.squeaky comes to visit-not good.

Side note-overly rich conditions at the wrong time,can make this a lot worse,IE accelerator pump timing-if the accelerator pump sprays as this phenomenon occurs,it adds fuel to the (mis)fire,making it worse.

   Happy Tuning

    Mike

05 210, do you remember SATURDAY NITE LIVE....The Mr. Bill Show, this was the mental picture that flashed thru my old brain,Mr. Squeaky,new term for the boat dr. to use on clients that will not properly store a boat motor,2 strokes love lean. thanx that was a good hardy har har...........boat dr

Thanks folks for the suggestions. I'll have the mixture and fuel pressure check before we get back on the water in April.

thanks

GottaSki wrote: I'm thinkin its a clogged tank screen

Quite possible, as the boat sat for a number of years with out running, except for winterizing and summerizing....

Q, anti-siphon valve. I hate those.

ultrarunner, I had the same problem this past spring on my 89 nautique. It almost drove me crazy looking for what the problem. I adjusted the float, took apart the carb, changed the fuel filter, checked the fuel pump pressure, checked the fresh air hoses for kinks, birds nests or other blockage.

I went to see Woody at Southeast Correct Craft and described the problem, without hesitation he said "your anti-siphon valve is clogged". I took the valve off and it was exactly as he decribed, the screen was clogged on the fuel tank side just enough that the fuel flow would not keep up with demand at wide open throttle for more than one minute.

The anti-siphon valve is on top of the gas tank and is between the nintey degree connection from the tank and the fuel hose to the fuel pump.

I would check that and clean it before doing anything elae.

In the process of disa$$embling my 87 SN I removed all of the fuel and the fuel cell. The last gallon of fuel came out brown from all the whatever lurks in the bottom of a fuel cell for 20 years. Could definately understand why clogging someplace would create an issue.