The Stovebolt Site Forums The Shop Area Engine Shop Rochester B running rich

It is sure nice to have you fellows that have dealt with these things. Yeah as a kid the stuff was newer and I never had problems. And they weren't all from rebuild places either.
When I first did this, it was a wam bam deal to get it done. Now its a study, of this and that sort of deal. Thanks to you folks I have more stuff to check and figure out. So where to get the proper size seat if mine isn't? I just looked at the jet number now I want to actually check it.
Question the idle port on the side opposite the vacuum port, goes up into the air horn to a small stepped hole, that is hidden, and was drilled at the factory and that drill pass through location is plugged on the upper area of the airhorn. I tried to feel for a hole with small wire, there has to be one some where because it won't pull a vacuum on that port. So is that a vent or air bleed?

Back in the day, to get good training, you sent your young mechanic to Rochester, Carter etc. sponsored training classes. The school had the tools, equipment, parts, diagrams and specification sheets (big thick carburetor book). Students received theory and hands-on experience. They were graded by completion of tasks. As far as I know none of that exists today except maybe becoming one of "Carbking's Padawans".

"So where to get the proper size seat if mine isn't?"
This is covered in carburetor school. First determine which model Rochester carburetor was factory installed on your vehicle (or if transplanted, engine) when it was new. Compare this with the ID tag held by a fuel bowl screw on your current carburetor. If you don't have a tag (big frown), you use your Rochester Service Manual and compare the throttle assembly base stamping to the model listing BUT if the numbers agree this doesn't mean all the other carburetor parts are correct. The service manual specification sheet for that model will list the drill sizes and other needed data. The Rochester/GM fuel valve part number would be listed so one could be ordered. If the carburetor on the engine was the wrong model, the mechanic would inform the vehicle owner and replacement options would be discussed.

All of the above is a fruitless pursuit if you are running the vehicle with Ethanol gas that has been sitting for years in a standard steel fuel tank.

Back in high school (when we had genuine gasoline), the commonly used main jet in the 235 Rochester was either 56, 57 or 58. 56 was lean, 57 was normal and 58 was richer. We all mostly used 57 because we were at 5000 feet elevation. Today if you're using ethanol-laced gas, a jet one size richer will help compensate for the change ethanol provides...ethanol will actually generally burn leaner. The main thing is to figure out what mixed breed of parts are in your Rochester and then figure out if they're warped (and how much) and by the way...you have to also make sure the inner part of the carburetor isn't warped also.

Some folks will preach "use 2 gaskets" for a fix when the castings get all warped. The attached image is one reason why I don't like to see that done. This duo of gaskets was removed from one of the Rochester B models. If you look very closely you can see the person trimmed one gasket for the main jet mast and you can see the interior part of one of them was sucked into the carburetor's bore and that turned it into a vacuum-leaking and gas sloshing mess. Every time the vehicle went around a corner and the gas ran up in the float bowl, it would pour right into the throat of the carburetor.

Here are my latest findings, the stem on the power valve was bent .020 TIR, 1" vacuum will start moving the power valve I have not tried to determine at what point the check ball seats or unseats, I'm guessing around 5" like the manual says is the opening point (ball unseating).
By 10" the power piston pretty much bottomed out.

Since I have 3 other carbs, took them apart, one had a .100 gasket for the float bowl and airhorn, the main jet stem or well was on top of it, and that carb had a weaker power piston spring than the one I'm working on.
Something important, the throttle body to intake manifold gasket that comes with the kit has four slots in the bore, not all those throttle body's are double drilled, the one carb the vacuum port was blocked by the gasket. I bet they just gave up on that one or ran it rich forever.
The other carb had the float bowl gasket on up side down and that was locking the power piston and keeping the valve open.

The jet looks close my drills were either too small or too big, missing the one I needed, yeah torch cleaners the same big or small.
The needle valve seat hole is .100 is that good?

Go back and look at Jon G's fuel valve picture. You have the Big Daddy.

The Walker Products catalog lists 31-506 (0.091").
Good luck to you. I'm bowing out on this post.

Yes, in that image I posted the middle one (with 2 grooves) is the .091" opening. The one on the left side is .076" opening (which definitely came from a B used on a 235) and the one on the right side is either .100 or .110...something like that. I would have to dig up my notes. It was an aftermarket product of unknown make and age. Most of them had seats of about .091"...which is larger than the Carter, but the float bowl is larger on the Rochester.

Is .100" good? Well, the area is 20% larger than .091" so there's that. Area of .091" is .0065" and area of .100" is .0078". .0065" x 1.2 = .0078"

I will mention all the carburetors I straightened were also rebuilt and tried on my 1959 235. I tried one of them with three different jet sizes and then I tried the same carburetor (which was actually a BC model) with three different seat orifice sizes. And then all 5 of them were sold right here. Which worked the best? The smaller fuel inlet orifice (I had one which was something like .080" I had saved from the 1960s) and the 57 size main jet seemed to run nicer at idle and city speeds. I didn't try them on the highway. But no matter how hard I tried 3 of them ran richer than they should have. 3 had manual choke and 2 had auto choke. One of the BC models was a carburetor I had used since the early 80s. It wasn't too bad after I went totally through it, but there was no comparison to the Carter YF.

Yes that is something that such a small amount is a huge percentage difference. So if I can find a piece of small brass I guess I could plug it up and drill a smaller hole then? Jon in your opinion is it best to set the float level at the specified 1 9/32 or go a bit more for less fuel level?
The carbs I took apart the float drop was into the bowl past the specified dimension.



edit a 2nd time for my dyslexia

Good news, the inlet seat hole is stepped. I had just quick checked with calipers the threaded end opening. Looking in I could see a small step, I can't fit a .089 pin through(it does go down to the step and stops), next step down was .085 it passes through(guessing .086 to .087 for the hole). So I guess they knew what they were doing with this kit.