IGTMYKX

Please check my mods.
Having a problem with rich fuel mixture that is causing car to backfire thru exhaust. Car runs good above 55 mph. Sometimes on startup idle is rough; other times idles ok. Started car yesterday and ran ok for about first 3 miles at 40-45 mph. Stopped for traffic light and then notice rough idle. Backfires and pops until I can cruise at 50-55 mph and then cleans itself out and runs fine.
Have replaced both power valves and installed rebuild kit; replaced dist., cap, rotor and replaced with 50,000 volt coil; replaced spark plug wires, am using hot spark plugs.
One other note - replaced ignition module several weeks ago (seems like poroblem began after replacing.)
Any advice would be appreciated)

bigvette1

Hook up a vacuum gauge inside the car with a long hose to manifold vac. Then at the speeds where it loads up, what is your cruise vacuum? Maybe the power valves are not correct for what kind of vacuum you are pulling at idle and acceleration to 50, causing them to pore it in. The other is are you over carbed for the engine? Get some other opinions.

IGTMYKX

The carb has been on the car for probably 1 1/2 years. However, we just did get the secondaries working properly.

Larry B.

Sure sounds like a blown power valve. It could also be a sticking needle and seat. Holley's aknown for both problems.