Wide open throttle backfire

"My 1990 omc 4.3 liter is abou

"My 1990 omc 4.3 liter is about to drive me insane. The boat runs like a champ untill you get around the 4000 rpm range. Seems to backfire or pop through the carb. You can back the throttle off just a touch and it will pur like a kitten. Sometimes you can push it up to 4500 hundred and will run fine for a moment then start popping. Iam lost. New carb, points, condensor, plugs,and coil and even cut out some of the purple wire thats a mile long going from the coil to the alternator. Boat runs wonderful until that 3/4 throttle mark. I was wondering about the resistor and its location. Was thinking that maybe it is getting hot and breaking down. ANY IDEAS ANYBODY."

"You don't reallt have a r

"You don't reallt have a resistor per say but a resistor wire that goes between the coil and the alternator. Could be a lean condition causing the backfiring, I would replace the fuel filters, the one at the carb, the water/fuel separtor (if you have one) and possibly check the anti-syphon valve at the outlet of the tank. Is this a 2bbl or 4 bbl, I think those 4 bbl had the infamous OMC Spifire ignition, the 2 bbls had points, could even be a timing advance problem within the distributor."

"Hey bob, I do have a 2 bbl ca

"Hey bob, I do have a 2 bbl carb. I have checked the the timing advance and every thing seems to be workin fine there. I have even put a light on it and checked the timing and checked to see if it advances when throttle is given and every thing seemed ok. replaced all filters. The antisyphon valve iam not familiar with. Have noticed sometimes when iam fueling that fuel splashes out a vent looking valve back beside the gas cap. Is that the antisyphon valve. Also do you by chance no what color the resistor wire is. If i remember correctly there is three wires coming off the back of the alternator. Dont no if this has anything to do with it but i noticed that the alternator gets hot as he## when the engine is running. Layed my hand on it the other day and didnt take me long to move it. Thanks bob!!"

"The "vent looking thing b

"The "vent looking thing back beside the gas cap" is exactly that, a vent. It is normal for fuel to come out when the tank fills. The anti siphon valve is in the line from the tank to the fuel pump. It is a safety shut off in the case of fuel line breakage. The fuel pump has to overcome the spring in the valve.
What is the condition of your plug wires? You have changed all the other ignition parts, might as well spring for new wires. Probably need them. Also, I would recommend checking the fuel pressure from the pump. You can get a fuel pressure gauge at Autozone to install temporarily between the pump and carb. Monitor the pressure throughout the RPM range to see if it is keeping up.
Hope this helps"

"The resistor wire actually co

"The resistor wire actually comes from a splice between the coil and alt. The color at the positive post of the coil is purple with red and splices into the purple wire from the alternator, the other part of that splice continues on as purple to feed the ESA module.

You've got me real curious now when you say " even cut out some of the purple wire thats a mile long going from the coil to the alternator " was this a solid purple color because there shouldn't be a purple wire going directly to the coil, should only be a purple/black (feeds 12v during starting) and the purple/red (resistor wire) I sure hope you didn't cut some off the resistor wire "