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im trying to TS a backfire thru carb problem on my 62 gal xl 390 holley 4bbl mild cam fpa long tube headers 10 to1 pistons pertronix ign.it didnt have this problem before i rebuilt the holley 1850 and installed a pcv into the intake adapter i got from t-bird products.would the addition of the pcv cause my carb to go lean or rich.the timing is set at 12 btdc.ive got 20hg vacuum in park if i put it in drive it dies imediatly and pops back thru the carb.so far ive checked for vac leaks and checked the firing order.havent pulled the plugs yet but there only 4 months old wires were changed last year.i dont have a dashpot.id like to get the holly to work as a new edelbrocks is $$$$$.
 

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Quick diagnosis is to disconnect PCV from carb. Plug line to carb and vent PCV to air. If it still backfires then the PCV is not your problem. Look at the carb. Did you replace powervalve or use old one?
 

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im trying to TS a backfire thru carb problem on my 62 gal xl 390 holley 4bbl mild cam fpa long tube headers 10 to1 pistons pertronix ign.it didnt have this problem before i rebuilt the holley 1850 and installed a pcv into the intake adapter i got from t-bird products.would the addition of the pcv cause my carb to go lean or rich.
The addition of the PCV System will cause the mixture to go lean (controlled vacuum orifice). This in addition to the headers will make for a very lean condition as evidenced by the lean backfire.
 
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