Back Firing

sg1747 · #1 01-25-2009, 07:50 AM

I have a 69 Z with a smog pump and chambered exhaust that back fires when I let off the gas or downshift. Does anyone know what the cause could be?

John

**ssl78** · #2 01-25-2009, 08:59 AM

bad diverter valve or vacumn signal

**Salvatore** · #3 01-25-2009, 03:46 PM

John, What car did you buy? Any pictures? Sam

1randy · #4 01-25-2009, 04:53 PM

Possible exhaust leak

sg1747 · #5 01-25-2009, 06:22 PM

http://i708.photobucket.com/albums/w...7/DSCN2120.jpg

jtower1969 · #6 01-25-2009, 09:05 PM

I'm no expert....but I would vote for lean. Colder temps have more oxegen in the air...you need to put more fuel in the carb to equal this out. I have a baseline for my car and adjust air bleeds up or down 1 1/4 turn before changing jets.

**Xplantdad** · #7 01-25-2009, 11:17 PM

I thought all smog set ups backfired to a point...which is one of the reasons that people took them off...

**napa68** · #8 01-26-2009, 04:59 AM

Judging by the hood, it's a cross ram. My vote, Too fat!
Excess fuel gets in the exhaust, A.I.R. does its job, wham...backfire! M.O.O. and $0.02

Tim

**Salvatore** · #9 01-26-2009, 05:23 AM

NIZZZE car John!

sg1747 · #10 01-26-2009, 03:49 PM

i wish it was a cross ram.wens i will block up all the holes in the exhaust manifold and try that.

john

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