still getting a few backfires

I'm not sure where to turn with this:
1992 SNOB 351 ProTech

Rebuilt carb (shop did)
new plugs
new gas/water filter
new pv
new accelerator pump

I'm still getting a few backfires when I hit it. The carb has been completely tested and redone. I had a hunch that it could be the following.

I do have a stereo system that could be screwing up the ProTech... not sure if it could or not. I have two amps, yada yada... but I a feeling that the stereo is drawing too much and screwing up the protech timing which is causing the backfires.   From understanding, the Protech system will auto adjust itself to keep the enigine timed where it should be. If the some sort of voltage drop was happening, could this be screwing with my protech?

My other thought it could be something simple. The boat did smell a little gassy... as it was dumping too much in the carb which may have cause the pops. Is there a good guide or instructions on how the screws should be set?

I can still seem to run it fine after I feather it up or slowly to plane and then wot is fine. Someone said to try some 91 octane instead of 87 and maybe it will go away... (yeah.. I know. things just don't go away by thmselves... but)

vaccum?

thanks fellas!

with a lobe knocked down the cam shaft?   Not sure what that is.

I can do a compression test and see.. but what will that tell me? I can pull stumps out and run at about 40 mph.......

I ran 91 in it today and it seemed better, but I did get one backfire at start up out of the hole.   It's very odd. I would think that the ProTech would either work or not work.. no run at 50 percent....

I can pull the plugs and check them out.

thanks much!

Hey Munday:

I have never heard of just one lobe failing on a camshaft. Usually they all go and during initial 20 minute break-in. Also, did the bearings in your motor survive all the metal from the failed lobe? or was it a gradual thing?

Last month or so, I help my father-in-law put a rebuilt chevy engine in his truck. The truck was old, so went with a long block from a local machine shop/engine exchanger. Got it all installed, start up great and 15 minutes later it was junk. Low compression and almost zero oil pressure after warm-up. Pulled the engine again and discovered that all the camshaft lobes were gone. Lots of silver sludge everywhere in the engine...it was now junk. back to the engine rebuilder, asked a few questions (how was it primed, break-in, etc), once they were satisfied I knew what I was doing, they gave us another. Installed the engine, went to start and....damn, junk. One cylinder sounded like it had sand in it. Back to the rebuilder...third engine has been running great so far.

Sorry for the long winded story, but the rebuilder told us that every so often a camshaft does not make it through the break-in phase. He gets about 3-4 per year! It was the first time it has happened to me AND the first time I have not personally rebuilt the engine. I wonder if the reground camshaft was not properly re-hardened (nitrited?). Anyway, just curious.

I had a ProTech on my 93 and it was doing the same thing...backfiring on acceleration. I tried everything from filters, plugs, checked timing, even removed and cleaned the gas tank. And like you, i had the carb rebuilt which it didnt need. Finally went to a PCM certified mechanic who called PCM and they told him that the ProTech module was prone to cracking and could short to the block. Bottom line is that he replaced the electronic ignition which cost me about 500bills but the problem went away.

the mechanic replaced the ProTech with a whole new electronic ignition system that PCM sent him. He told me that it was the current model that they use on the new engines. I got a new distributor assembly, a new electronic module, and wiring harness.

I couldnt see the cracks on my ProTech either. they are too small but its a dielectric breakdown and was intermittent. The problem you describe sounds just like what i was seeing. backfire and popping while accelerating. and temperature seemed to affect it too. at a steady speed, it ran fine.

Skiers Warf Extreme in Osage Beach Missouri is the Correct Craft Dealer (Lake of the Ozarks) that i went to for the service. they told me their mechanic was PMC certified.

Autolite 24's are the proper spark plug for your boat, assuming you have the standard 240 horse motor and not the 285hp ProBoss with the GT40 heads. I use Autolite 24's and my boat runs great- I dont think theyre part of the problem.

If you diagnose the problem to be the Protec, you have other options besides the kit that SkiDIM and PCM want to sell you. Check out a DUI by Performance Distributors. With this ignition upgrade and an Acme prop, my boat will keep up with a new 196 (330Ex) up to 35MPH or so. I picked up 200 RPM and a touch over a mile an hr. It would be the closest to a drop in replacement as you can get- it combines the distributor and coil in one housing. Price isnt cheap, by the time you get new spark plug wires, youll end up spending $400 or so. Still a very worthy upgrade, IMO.

In my manual, I don't see anything with the autolite 24.... I do show Motorcraft brf3m or autolite btf3m. Then a side note about

14mm plug awsf22 = autolite 763.   However.. I cant seem to find the 763, so I assume the the 764 is the replacement.

113 degrees, decided not to take the boat out and hide in the shade.. ugg

Sorry, i said 763, I meant 764. I put those plugs and it works perfect now. I changed to only running 91 octane also and I didnt have one pop at all yesterday pulling about 10 people wakeboarding full tank of gas.....   It was nice to have her back again......

So my theory of the low amps at the low end was not it. I think it was a mixture of the wrong plugs and low 89 octane that start the back fires.

hope this helps someone else.

cheers