1989 351 PLD-PR-R12/PP backfire under power
Hello everyone, (you can skip the beginning and go to bottom to cut to the chase)
My first post, after many years of getting great info from the forum.
The engine was running fine for the 1st month of the season, the kids took it out and complained of ruff running, idle fine but when gassing to pull skier, the engine would stall or RPM's drop and then launch, there might also be an occasional back fire through flame arrestor. On warm and cold starts, would usually have to give gas to start engine. So being the dad that I am, they come back, and I notice the idle speed was low (below 500) so I start adjusting the idle set screw and play with the fuel/air needles and now I really f'd things up. Back fires began to increase, and engine would quit completely under power within seconds of trying to run in gear to the point now where it will not even fire.
In trouble shooting, I have pulled the plugs and they were black with carbon. I cleaned them checked the gap and replaced (many times on the pull and clean throughout the past couple of days) and when I would replace them, I would get a couple of spurts than nothing. I had a mechanic (not marine) review on the boat and his observation was that the coil's spark was not very strong, yellow in color and had to be close to the ground to get the jump and no "crack noise". Of course I do not know what the "optimum factory setting" is for spark and noise. I am at the point now where I will try to jump the battery to the coil to see if that increases the power. On my micky mouse meter, the coil is not registering any volts with the key in the on position. Same back at the solenoid. Its odd because the starter has plenty of power so I do not understand that part of it.
The distributor is electronic so no points, but the firing problem started after I pulled the cap off to see what the inside looked like.
My 351 has been a predictable for the past 8 years I have owned it. I have replaced starter, solenoid, ignition switch, and now the coil and ballast resistor. The spark from the plugs looks the same as the one from the coil, so I don't think the wires are the problem there.
#1So: after pulling all the plugs & cleaning for the 10th time, replacing ballast resistor & coil, I got it to start with throttling, while doing that adjusted the idle set screw to get it to 750, and now she idles like a kitten.
Boats, love / hate relationship mostly hate
#2 the test run produced the issue from the beginning. As soon as I increase throttle and get under way, around 2000 rpm I get a back fire, within seconds of going under power. If I idle speed for a minute or two and then throttle down, it will cause a back fire.
Any ideas?
