Originally Posted by JonnyD757

I have a 454 Mag in my 22' Velocity. I am a new owner of the boat. First few times out the boat ran flawlessly. 73 MPH at 5200 RPM. The last few times not so much. I notices a miss when cruising at 3500 - 4000 RPM's. The motor starts to cut out a few times then recovers. The last time it cut out and only allowed me to idle at 1000 rpms. If I feed it any throttle it stumbled. It doesn't back fire, just stumbles. I idled back for 35 minutes and tried to get it on plane again and it ran up to 3500 then started to miss again. Got it home, rebuilt the carb (it was dirty), new plugs, cap, rotor, plug wires, fresh fuel. Checked the fuel pressure. All good. Ran it on the hose and sounded good. Could rev to high rpms with no issue. Took it to the river last night and couldn't get it over 1000 rpm's. I am running the Merc Thunderbolt IV ignition. I've seen where that could be bad but I don't know if a bad module would cause this type of miss.

Looking for suggestions.