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ive got a ford fe 390 that backfires when starting up.it has a crane rv cam holley 1850 600 cfm carb long tube headers and 9.5 to 1 pistons it was rebuilt 5 yrs ago.problem started after tossing the draft tube and putting in a pcv system in place of the draft tube.When it runs ive got 20hg of vacuum at thebaseplate vac connection.timing is 10 btdc.It alsdo has a pertronix ignition.
 

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are you picking up your vacuum at the base of the carb PCV port? if your getting your vacuum from an intake runner it will lean out a cylinder and backfire or pop through the carb.

Like F.Bird says you must have a breather to aid the pcv in evacuating the crank case!

Jester
 

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carb base gets full manifold vacuum.Dizzy gets ported vacuum from holley cab vacport.Oil filler cap has a breather .This is a stocksetup.

Sorry :drunk:I left out 2 words that are needed in that post (the P.C.V.) Below is how I meant it!!!!! sorry again:drunk: LOL age is crowding out my proof reading ability LOL:D Give this old fart a break!!! LOL

if your getting your vacuum for >the P.C.V.< from an intake runner it will lean out a cylinder and backfire or pop through the carb.

Jester
 
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