Dual carbs running rough

[snap2]

I have 2007cc motor in my 73 Beetle that won’t stay setup and after dialling them in the ride gets rough under throttle and starts backfiring.

I’ve tried multiple jets, checked pressure, ignition, wires and spark and they are all good. Mixture is set at 1-1/2 turns, currently using 55 idles and 145 mains on Empi 44s with CSP linkage.

I’m running out of options and if anyone has some insight, it sure would be appreciated.

Thank you.

[RLFD213]

Sounds like maybe it’s running out of fuel. When it does it again shake the car with steering wheel and see if it clears up. Maybe the tank has a blockage. Or maybe the fuel pump or rod isn’t set up right

[Rome]

Are you absolutely certain that the spark plug wires for the right head are going to the correct cylinders? Placing your finger on wire for #1 at the distrib cap, touching the wire with your finger, following along the wire; and seeing/feeling that it goes to cyl. #1? It's easy for the 2 wires to get twisted under the generator/alternator and end up going to the other cylinder.

Do you have a snail tool to measure the airflow at each carb when you have it set for idle? If so, measure the airflow at one carb's air horn with the CSP linkage connected. Then measure the other carb's airflow. If they are different- which I anticipate- disconnect the carb linkage at either the left or right carb, and remeasure. Chances are that the measurements will be very close now. If so, this is evidence that the linkage is not optimally set to allow each carb to get to its idle airflow settings. The linkage end can be turned one turn either in or out so that once attached to the throttle arm, the idle speed and both carbs' airflows don't change. Even 1 turn of the linkage throttle end can be enough to push (or pull) thr throttle of the one carb, or of the opposite one out of synch so that at increasing rpm you can have the symptoms as you described.

This is basic setup tuning on any dual carb setup, regardless of the linkage type or carbs. A synch tool which shows the definitive airflow quantity is best for getting both carbs to the same airflow and idle setting. Experienced people can use a 1' or 2' piece of garden hose held over the carb intake to listen to the pitch of the airflow and compare the pitch to that of the other carb.

[cletus_zuber]

You need to post this in the Performance forum, maybe Glenn will move it for you.

You'll want to provide more details also, those guys will want things like float height, what ignition, how its timed, how the carbs were synced etc, etc.
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1972 1302
HPMX 40's & 019

[Rob Combs]

Once you get over there, there will be requests for you to post pics of your setup and the questions that come your way will feel like a congressional inquiry; just know it’s all for your benefit and they’ll get you through it.

But…
Sounds like either idle jets plugging due to inadequate air filtration or a linkage setup issue.