The Stovebolt Site Forums The Shop Area Engine Shop Model B issues

I have a buddy who has a very original vehicle with a 216. He wants to keep it that way. Someone changed out the carburetor for a Carter with an automatic choke. His, of course calls for a Rochester Model B with manual choke and throttle cables, so we put one on it. I went through it and it was very clean, but I did completely disassemble it, cleaned it in a one gallon can of carburetor cleaner, washed the parts it as hot of water as what comes out of the faucet, blew 3,000 CF or so air though everywhere I could, put in a new leather accelerator pump and new gaskets. I adjusted the float drop and float level.
Here is the current condition.
It runs like a top.
When you shut it off. Fuel vapors bubble out on the left side at the airhorn gasket. The gas evaporates before it runs down the side of the carburetor. The screws are as snug as I dare turn them. While this is going on, there are bubbles percolating in the fuel filter located at the front of the carburetor. The filter is not hot to the touch. Not much more than warm.
Later on, there is a bit of gas showing up at the throttle plate shaft.
I haven't put a gauge on the fuel pump yet to see if the pressure is too high yet (the new metal top pump was put on in 2018).
Here is my plan.
Test the fuel pump pressure. What should the maximum pressure be?
If the pump pressure is within specs, how can I check whether the needle is seating on the seat in the bowl without taking it apart?
What else can I do besides throwing new parts at it?

I ran into some similar issues a few years back on a GMC 228 with a Rochester Model B (Note: this engine currently resides in Dellrose, TN). It turns out that I had several issues: heat riser valve stuck in the hot position, a vented gas cap that wasn't venting properly, and a fuel pump pressure of 9-10 psi. One by one I resolved those issues. The hardest one to find was the new 'vented' gas cap. I can assure you that cap is vented as I type this response! It seems to me that a fuel pump pressure of 4-6 psi is adequate. I bought a fuel pump from one of our preferred vendors and the problem was fixed. Anything over that could possibly be trouble for the needle and seat.

The ultimate solution was an engine transplant. Today, a 1955 235 with a Carter YF resides in the engine bay. I believe Jerry says it like this, "The ABC's of carburetion------Always Buy Carter!"

I agree with the ABC's of carburetion, but we are working on a nearly unmolested original and want to keep it that way.
Thank you for your input. I can't wait to hook up the pressure gauge to the fuel line to check the pressure.

I find I have to fiddle a bit with the float level to get things just right. With the level too low the carb will lean out and cause problems.

So where can one buy a leather pump these days. The pink ones that come with the kits are awful!

Carl - the gas is bubbling out because the castings are warped. If you do a search, you will probably find at least a couple of threads on straightening the castings using pressure, heat, and lots of patience; only to have the joy of doing it again in 3~5 years, and every 3~5 years after that. Jon G. and I have discussed it.

Truckernix - who do you think you might call to get a rebuilding kit with a leather accelerator pump?

Jon.

I'm curious about the rochester B casting warpage:

Could the warping be compensated by a more compliant gasket?
Would that eliminate the need to straighten them periodically?

I once used 1/8" nylon foam to make a gasket for a really warped intake on my toyota... maybe viton sheet or something would work for the carb?

Well, I didn't want to hear about the dreaded warping.
Hey Jon, can you delete your post so that I can keep pretending that I didn't already know that was the likeliest cause?
Its the least you can do. There's a pandemic going on, man.
Oh well...
CarlI have thought about that too, but there are a lot of intricate cuts which would need to be made. If that could be sorted out, and the added thickness didn't mess up the relative depth of other internal parts, I'd say that it might be worth a shot in order to preserve a much needed correct carburetor.

Maybe just use 2 regular gaskets?... I'm tempted to draw up a .dxf and laser cut some viton.

I think I remember Jon talking about doubling gaskets to solve warp. He said no.
Before you go hog wild, check the surfaces on a granite inspection stone...........or your kitchen counter.

Thick gaskets have been tried.

Double gaskets have been tried. Doubling the gasket seems to double the speed in which additional warping occurs.

As to the viton or foam??? Don't know, but if I were guessing, would guess it will work................................for about 3~5 years

Seriously folks:

One can build a show vehicle which one does not intend to start/drive in which case every bolt and nut should be as original as possible.

OR

One can build a driver, and make safety or performance or comfort modifications.

OR

One can "stay original" and fix the warpage on the Rochester B every 3~5 years. But if one is going to "stay original" then viton or foam gasket material is not allowed, it isn't original. Just like using viton fuel valves in the carburetor, which don't leak nearly so easily as the original Monel steel ones do.

The Rochester B (opinion) is simply a poor design. Not as poor as some others (I suggest to the folks restoring early Buicks that the most expensive component in the restoration of ANY Marvel carburetor is the automatic, underhood Halon fire estinguisher!).

And the Schebler Carburetor Company made a point of trying to attract the fire engine market; which I always found ironic, because that meant a fire engine was present to put out the ever-present engine fire from the Schebler carburetor.

And the Johnson Carburetor Company put a "heating plate" (that is correct, they ran electricity to the carburetor!!!) in the carburetor bowl to preheat the fuel for better atomization.

And for those of you truly in love with the Rochester model B, I have advertised on my website for over 10 years that you can have a FREE Rochester B with the purchase of three rebuilding kits. How many do you think I have given away in over 10 years? Well, you can count the number on the toes of your left hand!

Where is the "beating the dead horse" smiley?????

As one ages, one learns the most valuable asset that one owns is time! Fix it right, fix it once, and then use the future time saved for some other activity.

Have fun.

Jon

Good to hear from somebody who's experienced these things, thanks!

My model B is a bit warped, but I'm boneheaded enough to try out misguided experiments...
Looking forward to seeing what kind of tune I can put on it using my wideband O2 gauge!

Marvel updraft carbs are used on many many cessna 172s... didn't realize they made stuff for cars also. I could believe it's much tougher to design an automotive carb.

Ott3r

The aircraft versions are a modified version of a late Schebler design (about 1931), produced in the Marvel/Schebler factory AFTER Borg-Warner bought both companies and changed some names. Another version was the TSX series used on LOTS of tractors.

Totally different from the older Marvel designs.

There were hundreds of carburetor manufacturers in the USA. Very few survived into the 1950's. Car and truck - Autolite (began in the 1950's), Carter, Holley, Rochester (began in 1949), Stromberg, and Zenith. Additional brands for tractors, small engines, etc. Marvel/Schebler, Tillotson, Walbro. And then the "miracle" carburetors - Fish. There may be another or two that I have forgotten.

Jon.

Cool!
The 'forgotten history' of carb-tech is pretty intriguing.
I haven't messed with many types of carburetors... but I really like the Aisan unit on my '86 toyota truck!

If you have access to a flat piece of 3/8" steel, a drill, some screws/nuts/washers and a gas grill you can straighten Mr. Rochester. Here's how I would do it:

https://www.stovebolt.com/ubbthread...ing-the-rochester-b-and-bc-castings.html


Jon (carbking) and I discussed flexible gaskets in the past. We agreed it was an interesting thought and might work but again there are some challenges. And even if they do, you're still stuck with the Rochester B.

My first car was a 1936 Ford. It had mechanical brakes. There were very sound reasons you didn't want those even if you only drove at 30 mph or less. Like the Rochester B, you couldn't make the fundamental problems go away no matter what you did.

Good luck.

I wonder if this carburetor is one of the early ones with the thinner bosses and smaller screws. I understand they were more troublesome.

I would guess not, due to the vent hole in the drivers side of the airhorn. I believe than was added to the later models.

Carl - whereas the leaking is noticeable, the leakage is not the real problem associated with the warpage.

If the castings are sufficiently warped to see leakage, then the internal vacuum passage controlling the power valve actuator can suck air, allowing the power valve to always be open. Anyone own stock in Shell Oil?

And if one drives aggressively around corners, fuel can slosh into the vacuum passage on a hard turn, stalling the engine.

I guess if I were truly in love with the Rochester B, I would take a page from Holley's book, and try to obtain some of the super-sticky and expandable gasket material Holley uses on their end-bowl carbs (4150 and 4160), have a die made, and cut B gaskets. But I really don't think its worth the trouble. We sell maybe 7 or 8 B kits annually. Would take 50 years to break even.

Holley bowls warp as badly as the Rochester B. I have three engine fires (two on performance cars I bought new) in less than 9000 miles to prove it. Haven't used an end-bowl Holley since 1973.

Jon.

Ott3r, your question is a bit hazy, any warping is a no go on a model "B" it is beyond repair. Normally it's the air horn (the top piece), if it is warped there is no way to make it better. I have purchased many nos stock model B parts from a good natured fellow on Ebay (12bolt_tom). His prices are reasonable and service is fast. Also, it would be extremely rare to have a warped float bowl. The cause of your problem is from over tight screws on the air horn (4 large screws). If you need any more help or have difficulty I'm always here. Doc.

Thanks for the info Jon, Doc, & Jon.
This thread has given me several ideas
I'll post an update when I start working on the carb in earnest.

Jon's post about the vacuum leakage is 100% correct. And Doc, not to be argumentative, but of the 5 Rochester B and BC models I used in the study, 2 of them had warped float bowls...warped enough to need straightening. So, I couldn't agree it is extremely rare. As for the 2 gasket answer, please see the attached image of one of the 5 (which had been "rebuilt" by somebody who used 2 gaskets). As the arrow shows one gasket was sucked out or popped out and created a nice new vacuum leak and fuel slosher. Also I'll show the 3 different sizes of seat fuel orifice I found in these. Which is correct? The data no longer exists or at least a comprehensive search on my part (involving one gentleman retired from GM) couldn't find it. The Carter engineers knew the size of that orifice made a difference. In the 3211s, they used a smaller one to remedy the flooding problem. And I found 3 completely different strength of springs on the power piston. Jon tells me there were several different ones used. Did the "rebuilder" get this right? That is to say did he keep all the parts separate when the thing was left soaking overnight? I'd bet money against it. As I proved, these can be straightened back to within .0015"~.002" and personally I'll bet that exceeds the state of condition when they were new, but unless this is going to be a trailer queen, your friend might want his Carter back...to most eyes and minds it is an improvement over the Rochester.

OK here goes. In my personal opinion the model "B" is one of the best carburetors ever built as long as it is applied to what it was made for. Your fuel pump pressure should be between 3.4-4.5 psi. As for the leakage I would not open it up again, sometimes the problem is the miss match of throttle body. Two vs one vent hole. As far as the bubbling of fuel try putting two or three spring type clothes pins on your copper fuel line, they act as heat sinks. If this old time fix works then make a sink that looks more aesthetic. Many times someone in the past puts too much rubber tubing for line, the more copper the better. Metering jets can also be a problem but that means going back into the carb. .058 is the best all around unless you are at higher elevation. I don't know which rocket scientist decided a plastic accelerator pump is best, I throw away the ones in kits and only install leather. Tupperware and gas does not mix. I'll be here if you need me. Doc "don't know much but I live and breath model "B"

If I was a female I'd be in love with carbking, but VERY happy as a guy with a wife. He has many more answers than I do. I'm a model "B" fanantic but carbking has probably forgot more than I will ever know. Do what he says. Doc

Hello all
I just started having problems with my Rochester in my daily driver

1950 Chev truck
235
Cleaned and coated gas tank
Fairly new fuel pump
Lean lines
2 filters in line
One at the pump and one inlet at carb
Drive the truck 2-3 times a week, absolutely no issues

Started it up a few days ago, noticed rough idle and rich exhaust
I noticed fuel leaking at the throttle shaft and worsen when keyed off

To the carb to my rebuilder whom rebuilt a few years ago
He checked the carb, everything clean and floats did not seem to be sinking

Put the carb back on the truck
Ran it and a minute later, back to the leak
I can hear fuel flowing in the carb with the key off and see vapors coming from the carb

Your help is appreciated

Could be a few things, but obviously fuel flow isn't being stopped by the float/needle/seat for some reason. Too much fuel pump pressure? Bad float or float sticking against the side of the float bowl? Something along those lines, possibly.