Need help with a carb question !, backfiring when I let off the accelerator |
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Need help with a carb question !, backfiring when I let off the accelerator |
pin31 |
Apr 8 2007, 06:52 AM
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#1
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Member Group: Members Posts: 398 Joined: 30-January 07 From: Newport, Rhode Island Member No.: 7,492 Region Association: North East States |
Here's the data:
PO owner modifications: 1974 2.0L w/dual weber 40s stock fuel pump with pressure control unit (w/return line clamp backed off). pressure control unit = guage with a clamp on the return fuel line (PO installed for autoX). The idea is to restrict the return line to increase pressure from street driving 3-4psi (clamp backed off) to 7-8 psi (clamp restricting return line). My modifications: Removed points and installed Pertronix II electronic ignition. Have not changed/adjusted the timing Observations: Car starts fine, idles great (after initial 5-10 sec of throtle play when starting cold) Car drives great. Plenty of power in all RPM ranges. Running a bit rich (plugs are black) The car backfires when I let up on the gas (when driving more aggressivly in higher gears) not so much (or at all) in 1st or 2nd or when I'll taking it easy. Because the car runs great (except for the backfiring) I did not want to start blindly messing with the carb adjustments if it could be something else. Could it be: carb mixture? floats? pressure control unit? stock fuel pump instead of lower pressure carb pump? timing? etc....... What do you suggest ???? Thanks !! |
pin31 |
Apr 9 2007, 12:39 PM
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#2
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Member Group: Members Posts: 398 Joined: 30-January 07 From: Newport, Rhode Island Member No.: 7,492 Region Association: North East States |
Thanks for the suggestions !!
pfierb: I'm not the kid in the picture (although I probably did that) r-towle: backfire is from the exhaust (too rich). The engine was rebuilt with a cam for carbs (don't know which one). I've contacted the PO to get this info along with the jet sizes etc.. Joe Richard: could you explain? One of the carbs or one of the jets on one of the carbs? or both .......... rhcb: I'll look for leaks. I also have the Triad dual outlet exhaust/muffler rhodyguy: With the return line clamp backed off I should be around 3-4 psi (the way it is now). I've been thinking about ditching the PCU and stock pump and going with the rotary one. (even if it's not the problem). Any other suggestions or things to try????? |
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