popping through carb

[metacat]

I have a 1991 Four Winns 180 Horizon w/4.3 OMC Cobra 170 or 175 horse power. <br /><br />The problem I am haveing started last boating season but was very intermittent. Yesterday was my first day out on the water and it is much worse now.<br /><br />Here is my problem. I have a popping (sounds like a lean misfire) comeing back up through the carb. I do not experience this problem when accellerating from a stop to get on plane or when cruiseing under 3000rpm's. The popping is real bad once I am on plane and I go to full throttle over 3000rpm's. It also seems to do it only when the engine is at normal operating temperature. <br /><br />Also when I experience this problem if I shut the boat off or when it stalls when shifting from reverse or drive into neutral like it sometimes does. I have to let the boat sit almost like letting the engine cool before it will start.<br /><br />I have replaced the spark plugs, distributor cap & rotor, coil and coil wire. I have checked the fuel filter, it was a stone filter, and it appeared to be clean. Any and all input/advise would be much appreciated. Thank You.

 

[metacat]

Re: popping through carb

bump up

 

[DJ]

Re: popping through carb

metacat,<br /><br />Have you changed the spark plug wires? Sounds like crossfiring.

 

[metacat]

Re: popping through carb

Thanks for the reply djohns19.<br /><br />No I have not. I did inspect them though and they looked good down inside the boots and had no signs of rubbing through. <br /><br />I did just get inside from working on the boat and discovered this. Loss of ignition spark after boat is shut off when it is at operating temperature only. After engine cools, aprox a half an hour later it starts fine. <br /><br />If you would please re-read my original post. I mention this in the fourth section of that post.<br /><br />Since I have changed the coil and coil wire already, I am leaning twords the ignition module.<br />Although in my automotive mechanic experience I have never had a case where a faulty ignition module caused a backfire throught the carb.<br /><br />What do ya think? Should I go for the ignition module. I called a few marinas and auto shops to see if I could have it tested but they said no.<br />They want 125.00 for a new module. So I want to be sure before I change it.

 

[Hooty]

Re: popping through carb

Valve?<br /><br />c/6<br /><br />Hooty

 

[metacat]

Re: popping through carb

Hooty, what do you mean by....<br /><br />valve?<br /><br />c/6<br /><br />I don't understand. Please elaborate on that.<br /><br />Thank you.

 

[Yepblaze]

Re: popping through carb

A burnt valve will pop at the carb. Also do other strange things. Vacuum check for steady needle.

 

[metacat]

Re: popping through carb

ok will do. I'll check that also and get back.