1989 OMC 302 5.0 Ford Backfires Pops thru Carb Please Help!

[athorsvik]

I have done a lot of searching and found a lot of great info, BUT my boat still pops out of the carb when under load, the boat will not get up on a plane. It idles great, revs in neutral to over 4K no problem.

It is a 1989 Fourwinns 302 5.0 ford OMC
Whats been done
-New plugs, wires, cap, rotor, points, condenser.
-Timing set to 10deg
-Spark plug gap at .035
-Point gap .018
-Firing order set to1-5-4-2-6-3-7-8 (I tried the HO firing order but it would not start with the HO firing order)
-Rebuilt carb
-All new gas
-New fuel filter
-Compression check all cylinders at 150psi (+/-3 psi)
-Timing chain is tight no slop.

Randomly, i began removing one spark plug wire at a time to see narrow down the culprit. When i removed cylinder #1 wire the poping was not as bad, but boat would still not get up on a plane.

Engine is in great shape, very clean, no rust etc.
I am completely stumped on why it still pops and backfires through the carb?!?! Please help! Hopefully one of you awesome people on this forum can help me!

 

[Bondo]

Randomly, i began removing one spark plug wire at a time to see narrow down the culprit. When i removed cylinder #1 wire the poping was not as bad, but boat would still not get up on a plane.

Ayuh,.... Welcome Aboard,..... Have ya done a compression, 'n leak-down test on it,.....

Sounds like ya might possibly have bad valves,....

How much crud was found in the carb,..?? the old fuel filter,..?? in the tank,..??

 

[athorsvik]

Thanks for the quick reply! First off i just solved the problem!!! Second off i feel very dumb But all the info on this forum in other posts is what helped me fix it so thank you!

Turns out my timing was off by 180 deg and i was using the wrong firing order. The HO motor does use the 351 firing order!

How i figured this out was i pulled the valve cover and actually watched the valves move in relation to the dist rotor. Should have done this three weeks ago as this would have saved me a lot of time and all the money i spent on replacing items that were good.

Who would have though that with being 180 deg off and using the wrong firing order that the boat would actually idle nicely and run around at 15mph?!?!?! Granted it runs MUCH better now and has a nice V8 rumble.

Ohh well problem solved, happy and safe boating everyone!

 

[Redrig]

I'm surprised it would run let alone go 15mph with wrong firing order and being 180 out .

How did that happen ? When you were doing timing chain ?

Glad you found it

 

[athorsvik]

It happened when installing the dist and spark plug wires. It is crazy how well it ran with being 180 out and wrong firing order. Hopefully this will help someone else out in the future.