Stalls, backfires on acceleration, 1989 4.3L V6 OMC Cobra

[hughesra]

I am having problems with my engine. It is a 1989 OMC Cobra, 4.3L, GM, V6.

Initially, there were two times (out of about 10 outings) that it lost power at the high end. The first time the boat was heavily loaded, and I went over a couple large waves, when I tried to accelerate again, it had no power, took a few minutes before I could get up and plane again. The second time I was pulling a skier, and I was planing, then the engine went to about half power. After a while I was able to plane again, but seems to have less power. I had also noticed a couple times (when water skiing) that the motor would 'diesel' (run after turned off) for a about 5 seconds.

I took it in for a tune up. The mechanic replaced plugs, wires, cap, rotor, points, condensor and coil. Checked the timing and the compression (ok). Seemed to idle and rev okay, but when he put it back in the water, it would stall and backfire when he put it in gear (under load). Now, it will start and idle, but as soon as you start to push the throttle, it starts to stall, if you pump the throttle, it will rev a bit, but usually backfires (through the carb).

We have tried everything to do with ignition
- tried swapping back to old plugs, wires, cap, rotor, condensor
- tried other spare coil
- checked firing order (wires from cap to plugs)
- checked resistor wire (measured and bypassed) to coil
- checked advance on distributor (twisted rotor)
- checked cap (dry)
- disconnected the ESA module
(noticed that the new plugs, #1 and #2 at least, were pretty black with carbon)

Then thought maybe it was a fuel problem:
- replaced cannister fuel filter (no water)
- checked carb fuel filter (clean)
- when pump throttle, see 2 streams of gas in carb (2 barrel)
- choke looks okay

Couple things I noticed (not sure if it is good or bad):
- I compared the routing of the plug wires from the cap to the plugs to what is in the manual - it is off by one position (in the manual, #1 should be closest to the front, but on the boat it is one position to the left on the cap). Mechanic says it is right as it, manual is wrong.
- less stalling, backfiring if flame arrestor is off
- looking into carb - looks like unequal amount of gas is being fed to the 2 seperate barrels - port side I don't see much gas, but on starboard side I see constant sputtering of gas (when I start revving up the throttle).

Things do not seem to be getting better. Hope someone can help?

 

[subcrx]

Re: Stalls, backfires on acceleration, 1989 4.3L V6 OMC Cobra

doing same thing here on my 5.7L cobra. Retarding the timing seem to slow it down. I need to have my distibutor checked, its gotta be either that or too much fuel coming out of the carb. Do you have an electronic ignition?

Check this post http://forums.iboats.com/showthread.php?t=274514

 

[79Rude115]

Re: Stalls, backfires on acceleration, 1989 4.3L V6 OMC Cobra

Same problem here on 5.7 OMC after replacing the distributor cap, rotor, points and condensor. I think it is likely to be incorrect order connecting leads to dist. cap and/or the points gap.

Have you checked the timing and points gap? I have attached the picture from my manual, I am not able to tell exactly where #1 should connect in realtionship to the cap screws.

 

[hughesra]

Re: Stalls, backfires on acceleration, 1989 4.3L V6 OMC Cobra

Finally found out what the problem was. I gave up on the mechanic that was working on the boat and took it to someone new. The first thing they did was to check the points and timing - turns out the point gap was off by a bit and the timing was off by a lot.
The original mechanic had never re-checked the timing and that was the problem. I am not sure if he had checked it and then it changed, or he just checked it wrong. But after the timing was set correctly, it made all the difference. The boat now runs well (better than it did before I took it in for a tune up).
Thanks for your help.