Backfire!

[abelincoln]

We finally got to the point where we can fire the 48 V-12 again. Yeah! Its only been about 2 1/2 years. But it now has mostly new wiring, hoses, radiator, ignition system, headers, and a serpentine belt, all of which seem to be functioning. After much cranking and some starter fluid, the V-12 started with much noise, smoke and bad vapor out the crankcase filler pipe. However, the engine backfires just every so often, not regularly, but really loud, like a gun shot. There are new Reds headers, but no head pipes and mufflers yet. The carburetor is a bit damp on the base plate. Anyone have this experience? Or is it just because there are no head pipes? Suggestions for diagnosis?

Thanks

Abe

[Guest B1rdman]

only thing i would say is dont burn the old gas.

true there is no push rods to bend,

but the valve can stick open.

even worse it can wear a cam from sticking valves.

gene

[peecher]

This is almost always an ordeal lighting a fire in a V12 that's been dormant for a while. The gas wetted base of the carb sound like the Power valve is leaking and drawing in way too much gas. This will cause rotten running and some real bad smells along with some extra fire in the exhaust. Might check the spark plugs wires for the proper holes in the terminal plates ( no. 6 and no.9 are real easy to mix up).

Anyway it sounds like you're on the way. Is that serpentine belt staying in place? Like Gene says I've also encountered sticking valves upon firing up a V12 that has not run for a few years so that too may be in the mix?

[abelincoln]

Dee:

Thanks, I'll have another go at it, I suppose a vacuum check would reveal sticky valves, at least on the intake side. Gas was fresh this year, but who knows. At least the replacement fuel pump is sucking from the tank. Seemed like the idle was smoothing out despite the rifle shot noises before I shut it off. I'll see if I can figure out where 6 and 9 wires are supposed to attach. I didn't notice any mix or exhaust coming back out the carburetor. I rebuilt the carburetor, but its sat so long since that a power valve could be the culprit. At least the carb is on top, and easy to get at.

Serpentine belt has needed a few bracket tweaks, and I had to have the new water pump pulleys moved in closer to the housing. You need to get the pulleys aligned pretty close. Haven't tried high RPM or under load yet, but so far it is staying on.

Abe