55.2-59 Rochester 1 Barrel Carb Question

[Robert Crandall]

I am using a single barrel Rochester carburetor on a 1958 GMC 270 engine in a 1950 GMC half ton panel truck. I have learned from experience and from forums that a feature of these carburetors is that they leak fuel onto the manifold as is shown in the 'before' photo. I just put another kit in it. This time I sanded the mating surfaces of the top cover to ensure flatness. The 'after' photo shows a film of fuel already starting to show, but above that joint. I also notice a hole on the upper left side of the air intake. I have another carburetor that does not have that hole.

What is this hole? I did not find where it opens. Could fuel exit from that hole? Could or should it be plugged? Thanks!

[1project2many]

IT's been many years since I've even handled a Rochester 1bbl. I don't remember that hole in the side of the carb.

But judging by your pictures your problem has little to do with the hole. The bowl appears to be leaking profusely. There may be some leakage around the choke shaft but I have to wonder if the float adjustment is correct and if the operation to square up the bowl and lid surfaces didn't cause more problems than it cured.

How did you confirm the lid is square? In my '36 Plymouth I used a new gasket and watched the imprint left by lightly torquing the cover screws.

[Robert Crandall]

Thank you for your advice. I did not check square. I used a metal scale to look at flatness. I did not find major non flatness. I went around both mating surfaces with emory cloth on a block. That sanded some at the four screw holes, but not a lot. The float adjustment measures correctly.

This carburetor was on a Chevrolet 235 of unknown year when I got it. The GMC engine that I bought did not have a carburetor, so I made this one fit. That was in 1978. This carburetor has been working fine and leaking a horrible mess since then. Multiple kits have been put in it over these years. One time it went to a carburetor shop (back when such shops still existed.) I was told then that these carburetors just do that.

The spare carburetor that I found has obviously not been leaking, so I thought I would ask here about making this one stop leaking. I put a kit in this spare, but I could not get the truck to attempt to start, so I put the kit in this existing one and put it back on.

I recently found the correct carburetor for this engine. Once I find a breather for it and feel like reworking the linkage, I will someday go that route.

[geezer#99]

The float level might be correct but it’s obvious you need to lower it.
And don’t be mislead by the hackers that say that’s how those carbs are.
I think that hole is a bowl vent.

[Robert Crandall]

Hmmm. Thanks for that advice. I can have a look at that. It will be a while, though. Our weather is getting nice, and I like driving it better than I like working on it. I am lucky in that this truck is a pleasure to drive. I do make infrequent attempts to fix annoyances such as fuel dripping onto the manifolds.

[geezer#99]

Sometimes those annoyances become towering infernos!
I had a truck burn down due to a small fuel leak!

[1project2many]

I've been repairing vehicles for most of my life. Fuel and oil today flash (ignite from heat) so easily that it's sometimes scary. I agree wholeheartedly with geezer # 99. It's wise to get that leak repaired before it becomes a much bigger issue.

I would also try lowering the float setting slightly. Fuel was blended differently in the '50s and today's fuel doesn't always like the older carb settings. I would also use a gasket imprint as a diagnostic tool to determine if the top of carb and bowl are sealing properly. It may be possible to use two part epoxy to fill voids or low areas so the gasket seals properly. It may also be necessary to cut your own gasket out of thicker paper. Gasket making isn't hard, just pay attention while trimming and cutting. You might be tempted to use two gaskets but it's tough to make this work without finding an adhesive that can bond the gaskets even in a fuel-rich environment. If the bond doesn't hold the gaskets may deflect leaving with no seal rather than a better seal.

Good luck.

[Robert Crandall]

Thank you both for your added advice. I can move this adjustment up on the priorities.

Do you have a recommended gasket material?

The material that was in the kit appeared (but without measuring) to be about 1/32 inch. 1/16 should be easy to find.

It is odd to me that the coating appears on the after photo to be above the joint. Could it be blowing up there?

Thanks.

[geezer#99]

Any leak will blow almost anywhere.
Check this out. You might find some info in the technical section.

https://www.carburetor-parts.com/Car...ls_ep_274.html

[Robert Crandall]

Model BC for me! Perfect. Thank you very much for that.