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popping (backfire) out exhaust

Started by _LJ355_ , Jun 09 2009 08:09 PM

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14 replies to this topic

#1 _LJ355_

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Posted 09 June 2009 - 08:09 PM

Guys ive encountered a problem with the new motor

Starts idles fine but as it gets warm it starts to pop (backfire) out the exhaust

Tried another carb still does it although cant get the fuel pressure lower than 9psi

Double checked rocker clearance as per camtechs specs .016 intake .018 exhaust

No vacuum leaks anywhere

Tried timing doesnt make much difference currently set at 20deg

combo is

355
VN heads
Camtech solid roller 252/257 @.050
10.5.1 comp
750 bg tp single plane
MSD pro billet 6al blaster 2 coil

Any ideas ?

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#2 LXCHEV

Lotsa Posts!

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3,649 posts

Name:Brett
Location:Melbourne
Car:'76 LX - 383 Chev
Joined: 08-November 05

Posted 09 June 2009 - 08:15 PM

Mine pops when I foul plugs. You have extremely high fuel pressure for a carby. Why can't you get it any lower? What do the plugs look like?

Weird that it idles fine though, if it was fouling plugs, it wouldn't like idling.... good luck finding the problem...

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#3 _LJ355_

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Posted 09 June 2009 - 08:22 PM

Ive got this fuel rail that has shims to adjust pressure we have tried it with and without them it doesnt make any difference il post a pic to show

Plugs are light brown although 7 and 4 a little darker

Forgot to add it doesnt miss constantly it does it sort of now and then

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#4 _LJ355_

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Posted 09 June 2009 - 08:26 PM

Anyone got or used one of these fuel rails ?

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#5 _Torana308_

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Posted 09 June 2009 - 08:46 PM

Sounds like it is leaking fuel either out the vent tubes on the carby or the boosters in the carby, Run it with the air cleaner off and see if you can see fuel spewing into the carby. I am guessing it will be due to fuel pressure if it is.

9 Psi is alot of fuel pressure. Is it possible to borrow a holley reg and drop the pressure and see how it goes?

Other than that is TDC on the balancer definately TDC, Mine is 4 degrees out from new, and my mate was having similar problems until we replaced the balancer and found the real TDC

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#6 _ass308_

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Posted 09 June 2009 - 08:49 PM

could rocker lash cause poping ?

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#7 _Squarepants_

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Posted 09 June 2009 - 08:57 PM

Fuel pressure is too high, get a regulator.

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#8 _LJ355_

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Posted 09 June 2009 - 08:57 PM

Going to try and get the fuel pressure down have had it running with the filter off havent noticed fuel spilling in but will check that

Has a romac balancer TDC is right on

Starting to think maybe back the rockers off a little ?

Just weird how its fine for a minute or so then gets warm then does it