Guys, I've got a problem that's been driving me absolutely nuts trying to get a '66 Impala running for a friend. The car has got the 250 in it with a Rochester BV, and after trying two different carb bodies, taking the carburetor apart over and over again, I still cannot get the darn thing to work like it should. My problem is that when you hit the throttle, the accelerator pump linkage pushes down on the spring for the pump, but the pressure against the pump cup is too great and so the pump doesn't really discharge any gas. Just a tiny little trickle down the discharge nozzle. I've tried cleaning the thing over and over, and no matter what I do, on two separate carburetor bodies, as soon as I put it back together again, the pump stops working. I'm desperately hoping somebody knows what's going on, or where I should look. I've gotten to the point where I'm pushing to just swap in one of the V8s so I can work with a carburetor I understand, because this is without a doubt the most frustrating carb I've ever had my hands on! Thanks!
Here's a good thread to read to double check a few things, (I am assuming your 2 check balls are in place and functioning)http://www.jalopyjournal.com/forum/threads/rochester-1-barrel-carbs-problem-no-squirt.496401/ It has a really good link to this page explaining Rochester B acc pump http://www.oldcarmanualproject.com/manuals/Carbs/Rochester/B/1951-B/MCarbRoch1951-B_0009.htm Heres a good chart and diagrams you would receive with a rebuild kit http://www.chicagocarburetor.com/pdf/Instructions-Rochester-B-BC-BV.pdf But it doesn't have the specs to adjust the accelerator pump. It doesn't look like the adjustment is as variable as a 4g. If at WOT the pump plunger is close to being bottomed out it should be close. There should be a jet of fuel visible if the cup is good, all the orifices are clear, the check balls are in the right place (one should be aluminum, one is steel and larger), and the float levels are adjusted so the pump bore is filling up, and the fuel pump is working. I feel your pain, the only two things that are more of a pia than dialing in a carb are; getting a transmission pan gasket to seal, and choosing the right anniversary present.
This carburetor is the style without the small aluminum checkball or the pump screen. I think the issue is the discharge check ball keeps getting stuck. The gas is fresh, but I think it might be dissolving varnish in the tank as it's getting very gummy, so I'm wondering if that could be the issue? Perhaps varnishy gas causing the check ball to stick?
Take it back apart. Fill the pump barrel with some liquid that don't burn, & insert the pump plunger. With your thumb over the "T" shaped spring retainer, it should discharge down the venturi. If not, unplug whatever's in the discharge passage. It never hurts to run a ball deglazer thru the barrel to remove scoring.
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