<VV> Buick 215 troubleshooting question (No Corvair)

[Jim Burkhard]

Bill Elliott wrote:
> Car starts and idles fine, but as soon as you place any load on the 
> engine with light throttle it falters and bucks. Put your foot into it 
> and it catches and pulls away very strongly. Driving along, if you give 
> it just a little throttle, it bucks and falters... give her more 
> throttle and she runs great.

The fact that it cleans up with *increased* load on the 
engine steers me away from thinking the problem is with the 
ignition system.  With ignition, generally things get worse 
as the load gets higher and higher; they don't clean up.

> First thing I did was to pull the carb off. The carb looked nice and 
> clean, but it appeared there was some water in the gas.  Just to be 
> sure, I sent the carb out to a local pro for him to check it over and 
> rebuild. He reported that it was nearly new, had a little sediment here 
> and there, but overall looked good. He went ahead and rebuilt and 
> adjusted it for me.

The symptoms sound to me almost like a bad accelerator pump 
; if there's no pump shot on a sudden throttle opening, 
everything goes lean. But go deep enough in to the throttle 
and the power circuit comes in, making everything happy 
again.  Looking down the carb throat, can you see a pump shot?

The one thing that bugs me is it sounds like it still 
falters if you very slowly creep open the throttle while 
driving... we call this a "crowd" manuever.  Under these 
conditions, you shouldn't need the accelerator pump to keep 
life happy since there is no sudden rise of manifold 
pressure (or drop in vacuum, if you prefer). So under a 
crowd (say at 2000 rpm in top gear), does it have the problem?

I'm not too sharp on the ins and outs of the AFB... maybe 
somebody else?  You could probably disconnect the 
secondaries and see if it is the power circuit that comes in 
saving things or the secondaries... might prove helpful info.

curious...
Jim Burkhard