Weber carb set up help, Jetting seemed to help but still slight popping/backfire Options

[North Coast Jim]

Just finished a new 2 liter engine build with Webcam for carbs installed.
New Raby heads, Hoffman Eng, are used. New 44IDF Webers installed with cross bar linkage. Valve lash to spec and timing is spot on. Carbs are synched. Continue to hear a slight popping from only the pass side carb at partial throttle positions. Car starts and idles with plenty of power thru acceleration, but who knows I haven't driven one in over 25 years. It's a hoot to drive except for the Issue. Played with jetting to no avail. Any Carb guru's out there able to provide input to solve this dilemma.

(IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/confused24.gif)

[stugray]

I struggled with my carbs lately and just got them running better than EVER just yesterday.
No popping, no backfiring on engine braking (I thought that was just 'normal' until now) and it starts immediately on the first crank. And I have more power than ever.

A few things I learned:
1 - For the lean idle setting: Follow the instructions exactly -
A - get the engine a little warm with the linkage still hooked up , THEN Disconnet the linkage
B - NO MORE than 1/2 turn in from the adjuster touching the arm
if you cannot get it to idle like this (like a tractor) then go up on the idle jet before moving on.
C - once you get it to BARELY idle, check that both sides are pulling the same with your flow meter and adjust the higher one down (unless it dies).

2 - once you have it running decent and warmed up - spray carb cleaner around the bases of the carbs and where the manifolds exit the head looking for intake leaks. The engine will stumble/die if you locate a leak. FIX THE LEAKS.

3 - Synchronize at idle and at ~2500 RPM (or as close to as high as your flow meter can handle)

4 - If you use pump gas with ethanol find different gas or use Sta-Bil to eliminate the ethanol.
I was getting crusty deposits in the float bowls and clogging the jets until I switched to AV gas.
This only took ONE DAY after a complete rebuild with the ethanol 91 gas in CO.
Filters will NOT help this - the gas will absorb water while sitting in the float bowls, then evaporate leaving behind the deposits.

5 - Get a AFR sensor. I have been using the innovate unit I bought WITH gauge for $152 on ebay. It has been working fine for ~5 years now.

6 - The BIGGEST ONE - Measure the output of the accel pump jets. I did this by taking a small cap for a hypo-needle and wrapping a wire around it to reach down in the carb. I prime the pump jets, then stick the 'measuring cup' down in the throttle body and give the acccel jet pump one full pump. These caps held ~0.5mL and was exactly how much my "good" pumps were pumping.
The other side was only pumping 1/5 of this.
I took the accel pumps apart, cleaned them AGAIN and swapped all parts from one side to the other and nearly gave up UNTIL.
I switched the pump diaphragm from one side to the other and the crappy pumping moved sides.
I dug through my stash of carb parts where I had ~5 sets of accel pump diaphragms and found that I had mixed & matched sets.
They were NOT all the same even though the y looked like it.
I matched up a diaphragm with the "good one", installed it and then my pumps pumped the same from side to side.

Now the car runs like it never has before.

[Mark Henry]

98% of the time it's a linkage issue, both carbs are not opening at the same time/rate, they are going out of sync as soon as they come off the idle stops, etc.

See it all the time.

I struggled with my carbs lately and just got them running better than EVER just yesterday.

3 - Synchronize at idle and at ~2500 RPM (or as close to as high as your flow meter can handle)

If you have to do this you have a linkage issue. (IMG:style_emoticons/default/bye1.gif)

[stugray]

98% of the time it's a linkage issue, both carbs are not opening at the same time/rate, they are going out of sync as soon as they come off the idle stops, etc.

See it all the time.

I struggled with my carbs lately and just got them running better than EVER just yesterday.

3 - Synchronize at idle and at ~2500 RPM (or as close to as high as your flow meter can handle)

If you have to do this you have a linkage issue. (IMG:style_emoticons/default/bye1.gif)

Not sure what you mean.
It is easiest to get the linkage close to correct at idle, but this does not prove anything.
Getting it correct at high RPM (as high as you can consistently measure with your particular flow meter) is more important than at idle.
And the idle setting can fool you as some slack can come out of the linkage as the carb(s) rest on the idle adjustment screw(s).

I have the Tangerine racing cable linkage so I really only need to set it at one point (something other than idle).
And I have the carb where the cable comes from the pedal as the 'master' where I set the idle with the screw. The opposite carb has the idle adjustment screw backed out at idle and not touching the linkage arm.

If you have a crossbar linkage, having the vertical linkage pieces change angle as the throttle is actuated can throw the two sides out of synch through the range of motion. So for those it is even more important to check at more than one position and try to setup the linkage so the vertical links are as close to vertical as possible.