anyone on here have a similar problem with 454 popping at 4000rpm? Over the winter we did oval port heads bigger valves a mild cam(flat tappet) and an intake took the engine to the dyno and it ran great making pretty good hp and excellent torque. Now put the engine in the boat and get a popping sound so I changed the fuel pump to a larger one tried a different thunderbolt distributor and still at 4000rpm it starts. The engine runs perfect all the way up to 4000. Open to all suggestions thanks guys

Yes it’s quadrajet carb

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might of worn camshaft lobe off on an exhaust.

Hope not the cam we put it on the dyno to break the cam in property had it out a few times doesn’t seem to be getting worse if it were a lobe I think it would?

What spark plug wires did you use on dyno? Check them with Meter

Sierra wires what kind of reading should I get with a multimeter? Set on ohms 2860ish?

just start checking them look for one that's out also look under cap for a crack between posts. Double check fireing order.

I did do a new cap and rotor there was some carbon tracking in the cap not sure if it was from running last year or not. Anyway changed it out and still no different

Tried plugs also it’s popping out of the intake.

It could be tach like SB said. Have you had it at wot at like 3500rpm ?

The boat runs perfect right up to 3800 when I go wot to 4000 or a little above that’s when it starts to spit and sputter through the intake

You can put a vacuum gage on it and see if it has a bounce below 3500 and if you can't find anything else disconnect alternator I doubt it will do anything but have seen it with a crank trigger before. Also check for 12v

Alternator might have something to do with it that was not on it at the dyno. What do you mean crank trigger??

I had a problem with a crank trigger next to an alternator once the magnetic field was upsetting the pick up. Last thing to try unplugging alternator

Ok sorry I wasn’t familiar with a crank trigger. My engine does nit have one

Yes at first it was a really loud pop after me changing a few things it’s more of a sputter through the carb

If it ran great on the dyno but now it’s popping so the issue is likely in the boat, not the engine. Fuel lines degrade, anti siphon valves stick, crud and water in the tank. The mods may have pushed the line capacity over its limit?

Id start with bringing an auxiliary tank and run off of that for a few minutes then if it runs great then start with checking the anti-siphon valve and replacing the fuel lines. You may do well to drain the boat tank into your truck as well.

Its been twenty years years since I’ve touched a Quadra jet but some carbs can blow out a gasket etc if the back fire was gnarly enough.

Well I think I got it figured out. My main wire harness was not making good contact. Thank you for all the help guys lots of great information on here