Will Quadrajet Jet upgrades fix exhaust pops / bangs

[8DJA]

Hi All,
I have a 1976 C3 which is running the original carb.
I'm having issues at the moment with loud pops and bangs when I lift of the accelerator, I even noticed this evening that it I floor it and then lift of I get a flame pop from the exhaust.

The car has been like this since I got it and is running headers with side pipes.

I was wondering if it could be running lean due to the headers which is causing this and if so would increasing the Main jet size fix the issue?

Thanks for your help.

 

[johng]

I had a similar issue (pops and bangs on the overrun) recently after I fitted headers and sidepipes. I thought at first it might be an air leak in the exhaust, but refitting the exhaust with plenty of sealant paste made no difference. Eventually I bit the bullet and fitted a wideband oxygen sensor in the exhaust. This showed that I was running rich at idle, very lean at cruise and on the overrun and rich at wide open throttle. Screwing in the idle mixture screws fixed the rich idle, and raising the Adjustable Part Throttle fixed the lean cruise (and to a lesser extent the weak overrun). The pops and bangs have now almost gone, you can just hear some very gentle ones on occasion. I believe your 76 should have the same carb as my 78. If so the Adjustable Part Throttle adjustment is in this hole (although the hole may still be plugged if no-one has done this before).

You need to make a tool to fit down the hole and turn the screw anti-clockwise, maybe half a turn. Obviously without being able to measure your air fuel ratio this is going to be a bit of a guess.

 

[antijam]

I had the same problem on my '71 with the stock Quadrajet. Increasing the primary jet size might cure your problem but first make sure that the idle mixture adjustment is correct. Popping and banging on the overrun is most likely to be be the result of a lean idle mixture. Once the engine is warmed up this needs adjusting to maximise the carb vacuum. On most Quadrajets the idle adjustment screws are similar.
The driver's side adjuster on my carb is arrowed in the pic - there's another on the other side. The process for adjustment is well documented on the web - here - for example. and there are lots of videos on YouTube on how to do it.

 

[8DJA]

Thanks for the info, I tried resetting the mixture screws and used a vacuum gauge to set them to best settings which was giving me a ready of about 19 to 20 but still the same.
pops on overrun and also bogs down when I first put my food flat to the floor before picking up again.