Pop and back fire at 1/4 throttle-why?

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drtybttr

drtybttr

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Got a 73 Dart with a 318. When I am at part throttle I get a lurching poping back fire effect. When i unplug the vacuum advance it goes away. what is the deal? Anything helps. Have tried timing and carb tuning multiple times. Its a hol 600 carb and rebuilt distributor.
 
drtybttr said:
Got a 73 Dart with a 318. When I am at part throttle I get a lurching poping back fire effect. When i unplug the vacuum advance it goes away. what is the deal? Anything helps. Have tried timing and carb tuning multiple times. Its a hol 600 carb and rebuilt distributor.
Click to expand...

I would hazard a guess it's timing-related...

Where do you have the vac adv for the dist connected, ported vac or full manifold vac?

Does it happen with the vac adv disconnected?

What does your timing curve look like; initial, mechanical, vac and total?

How much vacuum are you making at idle?
 
octanejunkie said:
I would hazard a guess it's timing-related...

Where do you have the vac adv for the dist connected, ported vac or full manifold vac?

Does it happen with the vac adv disconnected?

What does your timing curve look like; initial, mechanical, vac and total?

How much vacuum are you making at idle?
Click to expand...

What he said. Don't mean to hyjack this thread, but thanks for your advice on my electric fan Octanejunkie. That thing moves some air and cools it off fast.
 
I have seen distributors that have a problem with the breaker plate go cockeyed when the vacuum advance pulls in and cause that. Does it have points or electronic ignition? If it's points check them also. If it's electronic check the reluctor gap. should be about .008-.010

Just noticed you say it's a rebuilt dist. I can tell you I have seen quite a few rebuilt distributors that were absolutely junk. Bent shaft on one. Another one never even had the bushings replaced and the shaft wobbled around like crazy. Another was assembled wrong. Check it over carefully.
 
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