Ya left one scenario out George; it could be an early flat top Rochester 'B'!!!
I understand and appreciate your logical approach to the problem, that’s the way I would have assessed it. But if it’s a ‘B’ then logic doesn’t seem to apply and I’ll be damned if I can figure out why. Many more knowledgeable than I about carburetion have come to the same conclusion about the Rochester ‘B’ and some expert shops won’t even service one.
Take my ‘B’ for instance!
I'm running a factory stock set up with a stock single stage fuel pump, it might even be the original, so I’m sure that it’s not putting out more pressure than the N&S can handle. For it to put out more pressure than it was designed for would be illogical. Generally this condition only exists when an after market high-performance mechanical or electric pump is installed. In addition to the glass bowl filter/screen on my pump, I have an AC sediment filter about 10" up stream of the carb which catches any fines that might get through the screen.
The floats are brand new (no leaks) it is meticulously set for balance, fuel level and side clearances. The N&S are brand new, and of course it is a Viton needle, aren’t they all now days, it’s not sticking, worn or damaged in any way and it has no dirt/debris/obstruction under it.
The mating surfaces of the air horn and bowl are parallel and the gaskets are new. They were stress relieved on a specially designed fixture to hold them flat with in a few tenths and then machined flat in a Bridgeport mill while bolted in their normal position.
This carb was completely gone through a couple of thousand miles ago. When I say completely I mean the lead plugs were pulled and all the passages cleaned to assure that there was nothing in them and new lead plugs tapped in.
I just had it apart a couple of weeks ago to check for any dirt or something, anything inside and all looks clean and exactly as it should be.
The power piston is free sliding in the well but not loose, it is straight and contacts the ball check smack dab in the middle, the bias spring is the right length according to the specs and not bent, rusty or deformed. The main-well has the correct gasket under it. This is an area that I often find improperly serviced. The kits usually offer a couple of choices of gaskets and quite often the wrong choice is made by the installation of the wrong gasket. This causes the main well to be cocked and misaligned with the power piston. During the tune-up, the idle screw was backed out about 1 1/4 turns for it’s final setting. The vacuum gauge was maxed out and steady at around 20 in.hg at idle.
This engine will start the first turn over by tapping the accelerator once when cold. Once it is warmed up and you shut her down it will start on the first turn without touching the throttle, that is within 5 or 10 minutes after you shut her down. If you let it set for a half hour or so it takes a minute or two to get it cleared out, acts like someone had been stomping on the accelerator and has it flooded. When I take it out for a run of say forty-five minutes or an hour she runs along just fine. Then when I pull up to a light after cruising along at 2500rpm the engine is running rough like the choke was pulled half way out. It clears up as soon as I take off again. I’m about 99% convinced that the problems with the ‘B’ are heat related but just can’t put my finger on the why.
If you have ever worked on is predecessor the Carter W-1 you can understand the need for a carb that was easier to service. It is the opinion of many that although the Carter carburetor was more difficult to service it was a much better performing and more dependable carburetor.
The whole concept behind the ‘B’ was to create a carburetor that was trouble free and easy to service. This is about the simplest carburetor that I have worked on and maybe that is the reason it has such poor performance, it’s just too simple. The addition of two or three more screws on the air horn would have solved many of the problems that it has. However the fact that GM persisted with this basic design for more than a decade shows you just how much confidence their engineers had in it. Or perhaps it was the bean-counters that just wanted to cover the cost of adding the Rochester/GM carburetor to their lineup.
I hate to do this but I’m now in the process of refitting a W-1 to my 1950, 216 to see if all that I’ve heard about them is true. This is gonna take a few days since I will have to make another set of fuel and vacuum lines for the Carter.
Denny Graham
Sandwich, IL
Last edited by Denny Graham; 08/13/2008 3:06 PM.
