New 5.7 marine power long block but backfires after 2500rpm

[chrisJet]

I put a new block in just over the past month.. everything runs great on the trailer but once im in the water and hit 2500 rpm it has a backfire and the rpm drops.. I replaced all the ignition components, you name it.. its a 2005 marine power with with a new marine vortec block .. got tired of the headache so I took it to tige.. they think its distributer but its brand spanking new.. it was doing the exact same thing with the old distributer that was out of the old block.. is there anything else possibly? sensor's on the throttle body or anything?? Im running out of ideas and want this damn think done. thanks.

[boatwakes]

It's the position of the distributor, loosen the distributor and rotate clockwise until you can't. I will bet the farm you have the crab cap ( flat distributor with wires coming out straight out the sides). The ECM takes care of the timing but only within 35 degrees, the rest must mechanically be set. Backfires can only happen when spark is introduced into the intake and it's too advanced and you're getting crossfire in the distributor. If you have a dtc scan tool, check the cam retard and it should be around 45 degrees. If not, set it there.

[chrisJet]

yeah it is the flat top cap with the plugs out the side.. its at the tige dlr now and they seem to think its the wrong distributor bit its the exact same one that came out the old motor just new.. ive tried it all so I said the hell with it and took it in.. I figured that was the problem as well but it was a bitch getting it in the right spot and figured getting it on the computer would be the best bet.. ill know more tomorrow, there closed Mondays but either a tps is cheep and moving the distributor is easy too when its on a damn computer.. I just want it going lol

[boatwakes]

Again, just retard the distributor by turning clockwise. Believe me I know about getting it in there, just spent 6 hours in a tight bilge of a damn chapparell that the mechanic didn't know what he was doing and had the distributor out of time. Get a long flat blade screw driver and after the dizzy is pulled, turn the oil pump flat about 15 degrees clockwise and then re-install the distributor. Unfortunately, the dealer is going to replace the distributor and may get it in the right position and then charge you for it. If you have the scan tool you can look at the cam retard and if you can get it to 45 degrees, you're perfect but plus or minus 5-10 degrees will still operate fine. If you have any detailed questions, pm me and I'll give you my shop number to walk you through it.

[ericinmich]

I'm with boatwakes, it sounds like the distributor is off one tooth. Mistimed engines are forgiving at low load/speed so until you get to higher rpm it gets by...

Google distributor jumpted (or skipped) timing, chevy small block.