bad Holly power valve cause backfiring?

[AmadeusCharger500]

Thats just one of my guesses. My 71 normally runs great but just recently it wouldnt fire up and as I was giving it some gas to start it actually backfired through the carb (what an excitement)
Its a 383 with a 770 holley street dominator.

Normally the car needs some gas to start so this was really strange. So I rechecked timing 15/35, rechecked vacuum 17g and reset the idle mixture screws. The car runs great but now after about 10 times driving it and getting it started in a different way (give it no gas till it fires) it still backfires about half the time.

Any help would be funktastic.

[mauve66]

a backfire can blowout a power valve unless you have the kit in it, i don't know about causing a backfire..........

[471_Magnum]

Back fires are caused buy ignition issues most of the time. Check your plug wires. Make sure 5&7 aren't crossed. etc.

[471_Magnum]

And make sure your advance mechanism isn't hanging up in the distributor.

[areibel]

 

a backfire can blowout a power valve unless you have the kit in it, i don't know about causing a backfire..........

Been there, done that- it didn't even take much of a pop to blow it out, I'd check it.

And most of the backfiring problems I've had were ignition or timing related, from a coil going bad to a slipped timing chain.

[firefighter3931]

Once the PV is blown the engine will run very rich and the plugs will foul in short order....exhaust will stink of unburnt fuel. 

A very lean mixture can cause backfiring but as mentioned it's mostly a timing issue with the valves being open at the wrong time that causes the backfire. 


Ron

[AmadeusCharger500]

So I put this off till yesterday when I decided I'm just changing the power valve and see how that goes. Well as I'm draining the front bowl I see the vacuum cap on the advance line is totally cracked. So it gets me checking all the vacuum lines. Big leak on the break booster and another small crack in a cap on a vacuum tree on the intake.

So I changed power valve, fixed 3 vacuum leaks, and replaced the gas filter.

Wouldn't you know it the car starts right away now.
Heck I might even get better gas mileage as well as better response!

thanks all for your continued expert advice.

Heath

[Paul G]

Isn't old school great. No lean codes to chase down. The engine had to run so poorly the vacuum leaks actually found you.