Hi, I'm having a carb problem someone may be able to help with. This 1950 Ford Coupe is a brand new build going through its initial start-up. The engine is a stock Chrysler 5.7 HEMI crate engine with a Holley 670cfm Street Avenger Carb. The ignition is handled by an MSD 6-HEMI Ignition Controller. Fuel pump is Carter P4594/72gph. On its initial start, the engine fired and ran immediately although there was too much choke, too high fast idle and too high curb idle. However, for an un-adjusted carb I thought it ran quite well. Next day, I adjusted the choke and fast idle with a cold engine, started it and ran it up to operating temperature. It idled along quite smoothly all by itself. I had other issues to deal with so didn't address the occasional "lean-like" pops and stumbles. There is no tach but it was idling just fine at maybe 600-700 rpm. I was addressing an issue with a mismatch between the temp sender and the temp gauge. To help determine the solution I was taking resistance readings at different temperatures to figure out what the temp sender was doing. This required shutting down the engine, taking a resistance reading, then firing back up to run the temperature up further. As mentioned, the engine was running just fine on its own. On one restart, I had a pretty healthy backfire through the carb which killed the engine. Now the engine still fires immediately but won't run without "blipping" the gas pedal. As soon as I let it idle down a bit, it stalls. Today, I checked a spare 6.5" power valve with a Mity-Vac to replace the one in the carb. I removed the power valve from the carb and checked it with the Mity-Vac. I was very surprised to see it test fine as the symptoms are just like a blown power valve. I checked the PCV and brake booster hoses and they were OK so I installed the replacement and fired the engine. There was no change or improvement. I'm certain the power valves are good so I'm stumped as to what the problem is.
My 442 eats power valves. I stock gaskets and power valves the way some keep extra TP in the linen closet. One carb back fire and it's tear down time. I have it down to a 25 minute install including ****tail mixing.
Since this is a rebuild check everything over plug gap , fireing order, timing, one thing mainly i would check is valves maybe need adjusting some could be to loose and some to tight. Let us know what happens. Good luck.
Does it "chug" and act like the choke is pulled...(rich) or act like it wants the throttle pumped to keep the accelerator pump actively pumping fuel (lean)
If it is a new Holley than it is not likely that you popped a power valve. The new Holleys come with a power valve protector. Sometimes on a back fire you pop a vacuum line off or one of those little nipply deals that are used to block a vacuum port, you may take a look at that. You may also check your control box, you may have fried a circuit. MSD boxes are pretty sensitive to electrical problems. hell last year at the HAMB drags we had an electrical storm the night before the races and several lost MSD boxes, no one got their car hit by lightning, just the static in the air.
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