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Old 01-27-2013, 03:44 PM
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ford 390 fe backfire at startup

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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Old 01-27-2013, 04:24 PM
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Check your choke setting? Whats your climate? And elevation?

Jester
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Old 01-27-2013, 04:47 PM
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its a manual choke

50 degrees at 500 ft asl
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Old 01-27-2013, 04:57 PM
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Ignition timing. With a PCV system the opposing valve cover or the oil cap has to be vented.
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Old 01-27-2013, 05:09 PM
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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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Old 01-27-2013, 07:07 PM
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pcv hose goes to

carb base gets full manifold vacuum.Dizzy gets ported vacuum from holley cab vacport.Oil filler cap has a breather .This is a stocksetup.
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Old 01-27-2013, 07:16 PM
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Quote:
Originally Posted by 62galaxiguy View Post
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 I left out 2 words that are needed in that post (the P.C.V.) Below is how I meant it!!!!! sorry again LOL age is crowding out my proof reading ability LOL 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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Old 01-28-2013, 01:11 AM
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Try changing the Holley's power valve from a 6.5 (stock) to an 8.5 power valve.
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