Weber popping question

[Dean Lampe]

According to my A/F gauge, I am really lean when I let of the gas at all rpm ranges. I believe this to be the cause of the popping. What is causing this? I seem to be running lean on the mains as well but that is an easier fix.

For future reference,

65 idle jet
120 idle jet holder
170 main
210 air corrector
f16 tubes
.50 exhaust/ float bowl valve
40mm chokes

380 ci 302 with 8.7 deck, Yates heads with huge CFM numbers.
cam - solid roller dur. I 244, E 247 lift 631, 666 110 LCA 106.5 LSA

My mixture screws are 3/4 turns out and everything is in synch. At the point when I hear the popping, the throttle plates are closed and I am off the gas. It must be either sucking to much air or not enough gas or a lttle of both. What is the diagnosis?

 

[BigB98]

I know exactly what you mean...I see my A/F gauge indicating the same thing and have the same problem with popping. Many have indicated that air is being sucked in by the exhuast slip joints or elsewhere. I have played a lot with trying to get it to stop, but no luck. I'm used to it now.

 

[Dean Lampe]

I just can't believe that I can't get it fixed. What are your jet settings? Where are the weber experts?

 

[BigB98]

This is an extremely common problem. Nearly everyone complains of it, it seems.

Different engine...Alum Shelby 482.

42 chokes
70 idles
120 holders
F7
170 mains
210 correctors

 

[Scott Calabro]

Hey Dean,

My Pro Touring Camaro had a leaky exhaust system, QTP electric cutouts (VERY LEAKY), and race headers with slip on collectors. It leaked like a sieve, you could see gas leak marks. I had the exact problem you're having. I had two O2 sensors, one in each collector, hooked up to two Edelbrock mixture LED's. The engine would go WAY lean after a high power run upon closing the throttles. BOOM! Sounded like a 30.06 rockonsmile, lots of fun scaring the pedestrians.

I don't know 48IDA's that well but Holley's I'm pretty good with, anyway I installed smaller Idle air bleeds on all 4 corners, removed the slip-ons and re-installed with red RTV to minimize leakage. The problem only showed up once in a while after that.

I think its the leaks at your slip on collectors/idle emulsion.

Best regards,
Scott

 

[Neal]

170 seems small for the mains. I run 175s in my 347. We tunes using EGTs on the dyno to dial it in. I experienced the exhaust leak issue. Definite problem area. After fixing a bumb header gasket it is spot on.