VCCA Home Forums TECHNICAL - GENERAL Commercial Vehicles Rochester model B carb

Anyone want to venture approximately what the value af a Rochester Model B Carb# 7005140 in pristeen condition should bring? Numbers are stamped on the bottom face of the cast throttle body shiny, no rust is 5140 and on the carb bowl is a cast number 7005604 (the 56 is in a circle and the 04 is in another circle on the carb bowl bottom and cast on the throttle body is 7005606. I took it off of a truck engine in a wrecked C6500 50 years ago cleaned it up and stored it in an old foot locker. I found it today while looking for some trailer light connectors. I don't have a 261 engine to put it on. I do know that I haven't run onto one for many years while shopping for Rochester model B carbs.

I sent an email to:

The Carburetor Shop LLC
204 East 15th Street

Eldon, Missouri 65026


They listed a Rochester Model B 5140 carb as being in stock, I haven't received a reply...yet

Anyone doing business with them?

Hi, what size engine did the carb come off of? If you still have it, I'd be interested. I rebuild carb's. A carb that has laid around for that long is surely going to need a rebuild kit. Oh and if you still have it, what are the mtg dimensions ctr to ctr?
TIA

Sorry, but when I said pristine, with the original coating intact, that is what it is. I carefully cleaned it when I removed it from the 1957 261 engine (the truck was running when they drove it into the salvage yard the same day that I took it off the engine for $5 I removed it, the distributor, starter and electric wiper motor I paid a ridiculus $35 for everything in 1997. I always wondered where the deceased farmer that owned the truck for 40 years kept his spare parts....The Carb has been in a footlocker ever since. I lost track of it and supposed that I has sold it.
I also rebuild carbs, mostly Rochester model B's. I try to keep one of each major change as a reference piece. I have bought every model B that I can find on eBay or at swap meets for $10 or less. some folks collect stamps or coins, I collect Rochester carbs, Goldenrod squirt guns and tire pumps and any kind of a grease gun that I don't have. I have traded a couple of Carter W1s for Rochesters, never have liked a W1 for anything newer than a 50.

Well I sort of do the same thing...rebuild old Rochester carb's. I too, buy off of eBay or swap meets. I've only been at it about a year. Right now I have 12 Rochester 1 & 2 bbl carbs to rebuild. I'll bet you can answer a question for me. I have a restored 55-2 series Chevy truck with a 7004468 carb. I get terrible gas mileage...11 to 13.5 /gal.It has the std .058 main jet. I'd like to run it leaner to improve SOME on my mileage. I'm thinking an .052 jet would help. What would you suggest? Any suggestions would really be appreciated. Excellent find on the spare parts!!
TIA

The jet would be the most unlikely cause. Is the vacuum power piston working and or stuck? Is the proper insulator under the carburetor so the notch lines up with the hole under the base of the carburestor.

Gene,
I would expect a quality rebuilder to know if the parts in the carburetor were operating properly. I don't have that much experience with the Rochesters but did find last year that that power piston can drive you crazy. I had a problem with the B on my '51 with PG on the SW Fall Tour. It would start, run but not idle too well and lots of black smoke at low speeds. Gas mileage was really poor. After a parking lot (at the Post Office) rebuild(?) all was good. That power piston can mess with our mind but once you understand how it works diagnosis is a bunch easier. Oh ya, turned out to be a sliver of greenish-yellow plastic. Still have no idea where it came from.

Yes I agree with Gene and Chipper. the power piston must work well to get the right mixture to the engine at the proper RPM and under the proper load. Also the insulator and the vacuum circuit from the base of the throttle body must be clear, this circuit originates at the hole in the bottom of the throttle body and goes all the way up thru the model B to operate and be controlled by the power piston. If that passage is crudded up or the insolator is on wrong or buggered up the carb won't work properly, also note the way the metal is cast between the throttle base and the float bowl and clean out the carbon and dirt that builds up in the voids, that crud will allow heat to transfer from the throttle body up into the float bowl, causing perculation, which ain't good. You need to really study exactly how the model B works to do a proper job of rebuilding one. There is more to it than just half hardly cleaning the float bowl and checking the main jet and having the springs and balls, needle valve and float set, and a new gasket set installed in the right holes. I have been doing Rochester model B carbs since the 1950s and I sometimes run into a strange problem. I also am not someone that loves the BC model, I have always had no use for that automatic choke model.

By the way, I expect that unless you have black smoke rolling out of the tailpipe a lot that the #58 jet is ok, that isn't bad gas mileage for a truck unless you have installed a set of larger tires and a 3.55 rear end. A #52 jet may be ok, but it seems a bit small for a truck with either a 235 or a 261 engine, and if you ever load it down.

Thanks everyone for your input. Since my 1955-2 Truck (235) was bought brand new by my Dad, I know the R-B carb pretty well. I still have the truck. And I have rebuilt the carb just recently. So I know the pwr piston is not the problem, nor is the insulator block. Since I'm at a mile high + altitude, I suspect the std jet of .058 as being a possible culprit. Also, I've noticed my spark plugs are slightly sooty black (to rich) but no noticable smoke from the exhaust.

I have changed the rear-end ratio from the std 3.90 to 3.38 and the tire size is 15 inch, just wider in the back. I think your right about .052 being to small so I've ordered a .056. See my truck at:

www.picturetrail.com/cjb40

Just curious, what is the steel line going over the top of the engine from the driver's side? Is it an oil or vacuum line? I couldn't tell if it tees off the wiper vacuum supply line or not.

I don't use the vacuum port as I've put in electric wipers.
What you see is a SS line that taps into the oil filter and goes into the side of the engine and pumps oil into the valves/tappets area. It just further helps to keep things nice and quite. I met a guy at the Good Guys car show a couple of years ago who steered me in that direction. So I put it in. Figured it couldn't hurt anything