Bing Type 53 Accelerator Pump Question

[jimmyg]

I'm helping a buddy with the stock Bing Type 53 (26mm) carbs on his '72 R50/5. We're rebuilding them and I see there is an accelerator pump as part of the main jet/mixing tube assy.

I'm curious how this actually works so I can verify it's operation when re-assembled.

I'm very familiar with Dellorto PHM carbs (R90s) and their accelerator pumps, as they use a specific jet to squirt fuel when the throttle is opened, via a small lever that slides on the carburetor slide. So its easy to verify a stream of fuel being squirted when the slides are raised.

But the Bing's have a much different setup, using a small spring loaded wafer/disc inside of the mixing tube.

Thanks for any guidance/explanation.
RPGR90s

[Rob Frankham]

The pump in the bings is fairly crude when compared to that in the Dell'Orto. The piston needle at the bottom of the piston stroke depresses the disc in the base of the main jet against it's spring. As the piston is raised, the spring pushes the ball upwards forcing a small amount of extra fuel through the main jet. It's there to help the the transtion off idle and has no effect at normal running speeds.

Rob

[jimmyg]

Thanks Rob, I was thinking that the slide needle was utilized as you described, but wanted to get some validation.