The Stovebolt Site Forums The Shop Area Engine Shop Rochester 1bbl Leakage Problems

I have a Rochester 1bbl carb that always leaks around the top of the float bowl. I have checked the float and replaced the gasket several times, but it always leaks! Sometimes it just oozes other times it drips. Has anyone else seen this problem? What should I do? Thanks!

Mine leaks very slowly around the gasket in the middle of the carb. (the gasket inbetween the 2 havles) It's hardly anything at all just enough to make ya mad. I rebuilt the whole carb and it ate all the new paint of it. All the 4 screws are as tight as i can get them. Anyone have an ideas on this?

sorry to tell you, but take the carb apart use a straight edge to check if the maiting surface is worped. If so use 1200 wet and dry sand paper on a sheet of glass and polish the surfaces.

I have heard that lapping them with sandpaper ruins them . . . don't remember the reason why and it doesn't seem logical to me.

The "real" solution was posted by "Carb King" and involved getting a FLAT piece of steel plate and mounting the carb halves to it using the mounting screws through holes drilled in the plate. Put the whole works in the oven and bake it and it is supposed to make the body flat again . . . only to warp next time you assemble it?

The best solution I have heard is to take the carburetor off and put it on a shelf somewhere and get a Carter carb.

Just a thought... can you use a sealant around the edges? If so, what kind to you suggest?

Ken - I recommend your solution. The Carter is an excellent carburetor. However, the fix on the Rochester will last several years. Sanding or milling the castings flat will not last due to the removal of metal.

Joe - sealants on the carburetor are not a good idea. And while the external drip is annoying to you, the real problem is inside where the vacuum passage is also leaking, and causing a rich condition.

Jon.

Wanted to take a picture before mentioning this. Take a look at the picture of the N.O.S. bowl in the link below. There is what appears to be a line all the way around on the gasket sealing surfaces, both external and the internal venturi area. This line is actually a "ridge" which "bites" into the gasket and aids sealing. Milling, filing, or sanding will remove the ridge in the effected area, and will provide worse sealing, even if the mating areas are perfectly flat.

www.thecarburetorshop.com/Rochestersealingridge.jpg

Jon.

It's been years since I saw one with the ridge still on it. Thanks for the photo. I've tried sealing these with Permatex Hylomar, developed by Rolls-Royce for sealing carbs. Success has been sporadic at best. My friend has a box of bodies and we kept trying them until we found one that didn't leak much. We finally replaced his dual ones with the Pinto carbs from Langdon. No leaks and they work far better. I am still running the one that doesn't leak much.

How successful was the bake method?

I am lucky enough to still have the ridge.. Would 2 gaskets work. The reason I ask is that I finally got the carb tuned properly and don't really want to change them if I don't have to. By the way, thank all of you for your responses!

Fred - the "bake" method works to restore the carburetor to its original condition. Bear in mind the carburetor was in its original condition before it warped. It will warp again. However by using heat and pressure to straighten the castings, the castings are as good as they can be, and the warpage is a gradual thing over several years. We have been using this method for probably 25 years, and with the exception of the costs involved, we have had zero complaints.

The real problem is the design in that only four (4) screws were used. Had more screws been used to hold the airhorn to the bowl, this thread would not exist. Note that the Carter mentioned by Ken has seven (7) screws holding the airhorn to the bowl.

Joe - I don't think two gaskets will work, but what do you have to lose? Try it.

Jon.

Fred - just reread your post about your friends duals. We try to suggest when using dual 1 barrel carbs that the owner use either (A) carbs with a mechanical power system ie Carter W-1 on pre-1949 Chevy 6; or (B) carbs with a vacuum power system which were designed to run in a multi-carb environment ie Carter WA-1 as used on Hudson Hornet Twin-H power. While other carbs such as the type B Rochester can be used, tuning becomes a nightmare due to the lack of different tension vacuum springs. Due to demand, we finally had to have different tension springs wound for the Rochester 2G series (2 barrel), but have never done so for the B. Typically, running 2 (or more) Rochester B carbs will have the power valve open at high vacuum. The owner then will downsize the main jets to compensate, and wonder why it runs lean at WOT.

Jon.

CarKing,
could you please elaborate on your comment about leaking vacuum causing a rich mixture. This is for my own education, I am learning something here!

Truckernix - most modern automotive carburetors have several different fuel delivery systems. We will exclude the pump circuit from discussion, as it is primarily used in transition.

Idle (and off-idle) circuit - provide fuel at low RPM when venturi velocity is not sufficient to activate the main metering circuit. Normal range up to maybe 1000 - 1200 RPM

Main metering circuit - provide fuel for more or less constant RPM from just below the end for the idle and off-idle circuits up to wide open throttle. Generally calibrated to provide engine needs at high vacuum conditions such as normal cruising.

Power circuit - provide fuel for low vacuum (WOT) conditions only. On vacuum operated power circuits, the power valve consists of some combination of a tensioned spring opposing engine vacuum. If engine vacuum is higher than spring tension the valve is closed - no fuel. If engine vacuum drops below spring tension the valve is opened and feeds fuel into the engine.

So from the above, when the carburetor is at WOT both the main metering circuit and the power circuit are providing fuel.

If the carburetor has a vacuum power circuit, then the engineer designates at what value of vacuum the power valve will be actuated.

On the type B carburetor, the vacuum signal goes through the center of the carburetor and is sealed at the bowl/airhorn seam by the airhorn gasket. If the airhorn is sufficiently warped such that this vacuum passage is not sealed, then the vacuum "seen" by the spring is too low, and the power valve can be opened prematurely, causing a rich condition. This is quite common with the B.

A similiar circumstance will occur with the addition of a "large" camshaft, which creates less vacuum; or the use of carburetors originally designed for use as a single carburetor in a multiple carburetor system. One can "tune" for both of these conditions, but tuning for a vacuum leak is a bit iffy.

This is true for any carburetor, not just the B. The manufacturers of aftermarket performance carburetors help the tuners in that they make available different tension springs (Carter) or power valve assemblies (Holley). Often jets are incorrectly changed when the real problem is vacuum control. As Rochester never really went after the performance aftermarket, Rochester did not provide the selection of tuning parts available from others. This simply means the tuner has to do more fabrication to use the Rochesters.

Often in the case of multiple carburetor set-ups, the novice tuner when confronted with the vacuum problem will put much smaller jets in the carburetor, and depending on his driving habits this can work. If a certain amount of fuel is necessary at a given RPM, the engine doesn't care if the fuel is coming from a large main jet, or a small main jet plus a power valve. If the owner simply drives to cruises, car shows, etc., and never uses WOT, this stage of tune will work fine. A more experienced tuner, in this circumstance, would leave the main jets alone, and plug the power valve. Again, calibrating the carburetor for cruise (at a lower vacuum), but not WOT.

Hope this helps, and doesn't muddy the waters.

Jon.

CarbKing,
thankyou for this explanation. I have read a few carburetor books and I have never seen such a clear explanation. I saved this one for future reference.

I suggest that this post would be a good one to keep in the technical reference area.