BBS accelerator pump variations.

[paulclark]

Rebuilding a BBS, I notice a version of the accelerator pump I hadn’t seen. There’s a clip halfway up the pump rod and the slotted washer is under it with the spring below that. Looking at an exploded view of the BBS it looks like this is a variation which I’m guessing is intended to limit the pump shot. Is that right? If so I think I should be able to install it the way I’m used to with no clip and the slotted disc on the rod above the bowl.

If there’s one thing I’ve learned from rebuilding carbs though, it’s never assume that the previous owner knew what they were doing and assembled it correctly. In this case i suspect the diagram is not a clear guide either. Or am I wrong?

 

[slantsixdan]

Yup, y'wrong about what you're seeing, and if you've been assembling your BBSs with no clip on the accel pump plunger stem, y'wrong about that, too. That clip is there to lift the bowl vent valve (round metal disc with slot in it, item 23 in this diagram) which sits atop the upper carburetor casting. Without that clip to lift that disc, you'll get bitchy hot start/idle behaviour and a tendency toward flooding. The clip needs to be in the slot corresponding to the throttle lever hole where the accel pump link is placed. Outer hole = lower slot, middle hole = middle slot, and inner hole = upper slot. The bowl vent valve opening dimension is adjusted to spec by bending the accel pump link at the elbow near the throttle lever.

The other arrangement is a plastic disc replacing item 23 there, and located underneath the upper carburetor casting. This arrangement is used on BBSs with a separate bowl vent valve ('70 California, '71-'72 50-state + Canada) or with no bowl vent valve ('73-'74, just as notorious for bitchy hot-engine behaviour as the Holley 1945s without a bowl vent).

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.