VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Need a spec '56 Rochester 4Jet float

Hi, folks -

I need a measurement or spec for my 1956 Rochester 4-Jet (forerunner of Quadrajet). I'm trying to set the float levels.

The "float drop" is easy, and my books all specify 2-1/4" no problem. That's with the floats "hanging down."

But the other measurement - where you hold the carb top upside down, and see where the floats are in the closed position - I CANNOT find a measurement! All the books and internet sources I can find say either:

(1) "use the guage included in your carb kit" (there was none) - or,

(2) "use Rochester tool # J-5339a." I don't have that. It's just a little cardboard piece to measure.

I'll attach two photos - the tool that the Shop Manual and Service Bulletin refer to, and a drawing I found online that shows what I'm trying to do. It also has text that specifies a dimension, but it's not specifically for my carb. It's for a Quadrajet, and may or may not be the same.

Can anyone answer this? Hope so - many thanks.

Need the identification number for the carburetor. With that, should be able to find the spec.

Be careful with the floats. Often, the 4G series used two different floats that look alike, except the arm is soldered on to the pontoons at different heights. If so, the higher arm will be the primary, the lower arm the secondary.

Jon.

Rochester 7008737

Yes, the primaries and secondaries are different visually. But I labeled them anyway, when I had it all apart!

I have a float gauge that was in a kit that I bought from Jon. Can mail it to you.

Gene - that would be fantastic! I'm stuck here, dead in the water - until I can get a dimension or a gauge, to set these up.

Do you know that your gauge would be the correct one for the 1956 Rochester 7008737 4-Jet? Since I can't locate dimensions, I have no way of knowing which carbs might be different.

It turns out Gene can't find the float gauge he thought he had (we've all been there!). So I tried to buy a gauge online, from Vintage Auto Tools. But even though it is listed, he doesn't really have one.

It's all really kind of ridiculous in a comic kind of way. All I need is a simple measurement. When properly adjusted, how far is it from the bottom-most point of the float, to the gasket of the carb top? (when held upside down) But instead of GM ever publishing that actual DISTANCE, they just do the "use Gauge # J-5339a" crap - and so now, it becomes impossible to adjust the float properly.........

I have a hand full of Burroughs Tool float gauges but they do not use the Kent Moore J number system. Does any one have a cross?

Also, I am not sure you measure with the gasket in place many instructions say measure from the bare surface.

I looked I don't have the Kent Moore gauge.

Dave

The Burroughs number is BT-89

Well I did not have the tool but I looked it up in my Delco carb service book and if you have the roundish floats in your attachment it is 1 5/8 both primary and secondary (with the gasket in place). If you have different floats let me know and I will give you that measurement.

Dave

Hallelujah!!! Dave, you are a gentleman and a scholar! Yes, it's the roundish floats. Now, I can put it together....

OK, finally got some time to finish up the rebuilding of this carb, and all adjustments etc. It's ready for a trial run on the '56 wagon, soon. Now I am confronted with another question - which gasket goes between the carb and the intake manifold?

I have no "old one" to go by, nothing was there. The kit offers a couple of choices, but no guidance as to which one is correct for which application. And I don't find any photo that is helpful in the Shop Manual or Service Bulletin.

The main difference is, the larger, simpler looking one would serve to block exhaust gases from actually entering the cavities in the base of the carb - whereas the more complex looking one would allow the gases to get up in there.

Compare them to the carb base/intake flange. If the openings for the throats are 2 large ovals at the base then use ovals. If there are 4 separate throats at the base use the gasket with 4 openings.

What you don't want is to have gasket sections hanging in the air ss it will be eventually sucked into the engine.
If you have the 4 holes, you could use the ovals as it might provide some balancing between the 2 sides of the carb/manifold. Look into the manifold to see if there are separate passages or whether they all open into a large plenum.

use the top gasket that allows more heat to pass under the base. The bottom gasket is for trucks that have the heat riser blanked off.
Came from the factory with the top gakket.

Gene - without knowing exactly what carburetor you have........the top gasket is probably Chevrolet, the lower gasket Pontiac.

But compare the gaskets to the mating surfaces of both the bottom of the carburetor, and the intake manifold.

Jon.

I remember what was used back when these cars were current and I worked in the parts department. Actually the original gasket was different for a Carter or Rochester. Also there are good picures in the parts book showing the (slight) differences between the Rochester and Carter.

Also my present experiance on my '57 which uses the same gasket as a 1956. I have been swaping betwen a Carter and Rochester carburetor last year. The modern gasket is cut so it will work on a Carter or Rochester as the differences around the heated areas ar slight.

Thanks, all. I will use the top gasket as advised.