I'm (still) messing with my Weber IDF carbs. They're tuned well except that one of the carbs pumps gas via the accelerator pump right away with the small flick of the throttle. The other carb doesn't pump until the throttle is turned a bit more. So it makes for goofy acceleration. Mine are early Italian carbs. I see that the modern ones have adjustable threads on the pump arms that I believe would allow to me syncronize. I spent quite a bit of time last summer rebuilding both carbs and while I was in there I replace each throttle shaft with new sealed bearings.

Here's my question: can the later style adjustable accelerator pump arms be retrofit onto the older style carb if the throttle shafts are also replaced with the newer style?

Thanks,
Marcus

Never mind. I finally found a decent photo of the later style and I can see that the bodies are physically different. Disregard.

A couple things:

Are you sure you have the carbs synched? One of them moving into the accel pump before another can be a giveaway that they aren't actually synched.

Yes, you could retrofit a later style pump body to an earlier carb. You'd need the pump bodies themselves with all of the hardware and the different actuation "cam" that is pinned to the throttle shaft.

Then you'd have the remove the butterfly plates and throttle shafts to be able to swap the cams over. Then reassemble with the newer accel pump body.

BUT,

Before you were to do that, check a couple things. One, on the earlier style accelerator pumps, there are two fulcrum positions that can be adjusted on the side of the accel pump body. If you look closely, there is a "1" and a "2". The second position provides a higher volume of fuel, earlier in the throttle tip-in. I would check that both of your carbs are using the same fulcum position. If not, it's easy to drive that pin out and move the arm.

OR,

Finally, a less likely scenario is that the roll pin that holds the accelerator pump cam on the throttle shaft may have sheared, allowing the cam to move. Or, it is certainly possible (ask me how I know) that you got the throttle shaft backwards somehow on one of the carbs, if you had to take them out to replace the bearings. They are drilled with an offset hole, so the throttle shaft won't work the same way in both directions.