48IDA drawing differently

[jhirasak]

jonalley,

I had a similar situation when I first installed a brand new set of 48 IDAs on my car. With the linkages disconnected, and the idle stop screw not touching, a similar range of air flow varience was noted between the two throats of a single carb and from carb to carb. Finally, I took all of the carbs off the car and made a temporary flow bench for a single carb using some PVC tubing to make a single carb mounting plate and a shop vac. This was to confirm that the flow variation was due to the carb instead of engine problems (leaky valves, worn rings, manifold leaks, etc). Using the shop vac test fixture, I equalized the air flow on all four carbs by drilling small holes in the butterflys on the opposite side from the transition holes so all of the carbs would read nearly the same air flow value with the butterflys completely shut. Upon later query to the Weber tuning forum, it was suggested that I should have slightly twisted the shaft to equalize the airflow on a single carb so both throats would flow the same value. In hindsight, I think that this would have been preferable to drilling the butterflys.

I would recommend that you take all of the Webers off the car and build you a test fixture so you can initialize the air flow on a single carb by using the method of slightly twisting the throttle shaft. After you have done that, then you can remount the Webers on your car and equalize the idle air flow by using the idle stop screw and the balance screw on the linkage between a pair of carbs on a single bank. Then, you can repeat the process on the opposite bank. This should bring you close to having the same air flow on all throats at idle.

Let me know if this helps your situation.

John