The Stovebolt Site Forums The Shop Area Engine Shop Float level , Float drop question.

What is the correct measurement for a Rochester b carb?
The sheet that came with rebuilt kit shows level at 1 9/32 and drop at 1 3/4.
Old service manual shows diff due to gasket not installed. It's on a 1954 3100 235 dual Rochester b. I did check the old interwebs but found many diff answers. I'm looking for an answer from someone who has the experience like most folks on here. Thanks so much in advance.

It won't matter where you set the floats if you're running two B's on a 235- - - -it's going to run lousy regardless of where you set the floats. If you insist on running that setup, set the float level as high as possible without gas dribbling out of the venturis with the engine idling. Set the float drop so it keeps the float from bottoming out against the bottom of the float bowl. Keep a good fire extinguisher handy, as the frequent backfires you're going to encounter will set the carbs on fire on a regular basis.

If you want that setup to run somewhere close to right, find a matched pair of Carter carbs for a 216, rebuild them both to exactly the same specifications, and modify the intake manifold stud spacing for the narrower throttle body bolt pattern.
Jerry

I'm not going to disagree, I've read so many post that carbking and yourself have posted. I just can't believe that I won't run 100%. I bought it like this so the previous owner was never able to drive it correctly. Last Sunday I gave in after so much time spent on these Rochesters. I tried everything. It runs ok but a boog is still there under hard acceleration. I changed intake gaskets and even smoke tested the complete engine with no vacuum leaks. I'm sure these carbs are warped some. Everything else with them are exactly the same. Acc pump works as it should nice stream when pressed. I was just going to try the float level one more time. I ended up buying zenith 228 from Carlos at carbsonly.com. Should be here soon. I'm just hard headed and won't quit sometimes. But these Rochesters deff kicked my a**.

You simply can't repeal the laws of physics. Carburetors work on Bernoulli's principle- - - - air velocity through a venturi develops enough vacuum to draw the fuel into the air stream. The slower the velocity (due to having two paths for air to travel instead of just one) the less fuel gets delivered into the airstream. Lean engines run like crap, and there's absolutely nothing you can do to change that fact in the real world.

For instance:
http://image.modified.com/f/tech/mo...+kickin_it_old_school+venturi_effect.jpg

This diagram is a little inaccurate, as the fuel level in the float bowl should be just slightly below the discharge nozzle to prevent fuel from being gravity-fed into the air stream.

"Wish in one hand- - - -etc."
Jerry

The following is copied from an article on our website, and adds to what Jerry has posted:

"For best results, the very best thing is to do one’s homework BEFORE one purchases anything. There are several major criteria in the selection of one’s puchase, but the first criteria is how the unit will be used. Consider that 50~60 years ago, dual carb manifolds were sold for RACING! Today, while a very small percentage will submit their vehicles to the race track, most are interested in dual carbs for either LOOKS ONLY, or looks with a modest increase in performance. These two uses have vastly different requirements in carburetors.

Typically, the manifold sold in the period would be drilled for two carbs the same size as the original (a 216 Chevrolet would have 2 S. A. E. size 2 carbs, whereas a 235 Chevrolet would be drilled for 2 S.A.E. size 3 carbs). By using this arrangement, the user could order a second original carburetor from the dealer to go with original carb on the engine. At the same time, the user would install a full-race cam, a magneto ignition, headers, high-compression pistons; all to go with a numerical higher rear-end ratio BECAUSE THE ENGINE WOULD HAVE AT BEST A VERY HIGH IDLE, AND VERY LITTLE LOW END TORQUE. This is a good selection for a trailered race car, but a poor selection for the “cruiser” on the street.

Since the manifolds of today are basically copies of the manifolds of yesteryear, generally the street enthusiast will need to modify the manifold for smaller carburetors. Example: for a stock or modestly built Chevrolet 235, the very best carburetors would be those designed for a Chevrolet 216. The manifold would be drilled for size 3 carbs (2 15/16 inch mounting pattern), but the 216 carbs are size 2 (2 11/16 inch mounting pattern). There are three methods of doing the conversion: (A) use size 3 to size 2 adapters (extra cost, and looks “hokey”); (B) slot the holes in the carburetor (no additional cost, but looks even more hokey); or (C) have a good welder fill the original holes in the manifold, and then drill and tap for the correct size (extra cost, but looks much more like a factory installation, and weren’t looks the major criteria?).

If you plan to use on a trailered racecar, use the larger size."

End of quotation.

And a bit more information:

There are three major methods of improving the atomization of fuel:

(1) Increase velocity
(2) Increase the amount of fuel (and watch some of it drip out the tailpipe)
(3) Add heat

A carburetor is calibrated for a specific venturi air velocity. If too large a carburetor is used, then the venturi air velocity will be lower than the design for the calibration. And thus will cause the engine to run lean.

Jon.