Okay I need help, I have twin 350’s in my 28ft Checkmate, and am afraid that it will happen again, some background on my problems, bought the boat early last season, had it in the water early ran great, one day decided to see how it would run wide opened, it ran great for a bit and then started popping through carb on one side, okay not good, I managed to get it home, pull top end off motors and messed up the valves, okay so I have the heads all redone, slap it all back together run it for about a month and bam, bad valves again, now I’m thinking it has to be reversion, set out on a mission to get performance exhaust, nothing would fit, turns out motor placement is to tight, EMI no good Stainless could not help, got burned by Trick on the hole thing nightmare, anyway I got a hold of the cam card and part number for the cam’s only 220 duration, so it looks like it’s not Reversion, so I think I need help on timing, or has anyone had this problem before, any ideas would be great, could it be pre-ignition? I have the timing set to 34 deg total advanced, I just can’t figure it out.

------Im no expert but it sounds like your engines are running lean. Fix it and fatten up the secondaries some, and also get more input than just me (LOL). I still have a valve out of my old Mistress (twin 540s) thats at least a quarter of an inch longer than when it was new. Did just what yours did and the miracle is that it didnt break off and destroy the whole motor.......Bill S

Timing will certainly do it. Depends on what heads and compression you are running. If they have fast burn heads, such as a Vortec engine that's way too much timing. About 30 degrees maximum. Lean A/F mixture will also do it.

Don't have fast burn heads, So I will see if I can ajust the carb, maybe bigger jets, don't know much about carbs only that they are 750's holley, I do however have a box of Jets that came with to boat, I'll have to see what is in it now and maybe step up, I think you go two up or two down? but a good place to start. Thanks, Fast Frank

Read the plugs!!

spend the money to set it up on dyno, then you will know exactly where you are at and what needs to be done.

Or spend the money rebuilding your motors.

What do you have for ignition boxes on this boat? Do you set total or do you set initual and add the boxes to it? Also how did you adjustt the valves? All food for thought. And do you have vacuum secondarys or Mechanical?

The plugs will tell you if it's lean and I agree with that diagnosis so far...

reversion usually shows up at idle

+1.

I have a buddy that it did the same us you, Stock 350 he was running the cheapest gas he could find, 87oct,It would tulip the valves , they put in a good grade stainless valve in it and told him to run 89, i think he;s still running the 87 but he hasnt had anymore probs, Just throwing a idear out there.Goodluck