The Stovebolt Site Forums The Shop Area Engine Shop Rochester B rebuild

Tuesday, I finished my first carb rebuild. I told my wife, there was no way in hell would actually run. Low and behold it runs, and has better acceleration then I've ever experinced in my truck.
I do have a question or two for the carb savey in the group...
First, the kit came with two smaller ballberrings. One looked as though it were steal, and the other some lighter color metal. I tore apart another B to find which to use (lighter color of the two). Can someone tell me the difference between the two?
Secondly; Although the truck runs fine at high speed, its idel is rough and it backfires through the carb under load when its cold. I set the float to an inch and 3/4 drop...could this be too low?
I'd appricate any thoughts.
Thanks much.
-Chris.

The color of the balls have nothing to do with it. You should replace any parts removed with identical parts from the kit. If you get the wrong size ball in an opening it can hang up & ruin the carb. Most kits contain more parts than needed so they can fit more than one application. The float drop doesn,t effect the running of the truck but the float level is critical. If it idles rough check for vacuum leaks at the intake manifold. Check compression of the cylinders. Stick with us & you can tell the wife " I told you so"

Thanks WB,
I'll check for leaks and recheck the float level.
Can't wait to tell the wife I told you so

On my model B i rebuilt, there are 2 "ball bearings" and i believe they are slightly different in size. I have an old repair manual, and I think it showed that all model B's are not exactly the same. The float level should be indicated on the instruction sheet that came with the rebuild kit. Possibly check your timing for your backfire problem.

I,ve been married a long time & I can tell you you are better off not telling her "I told you so".

They seemed the same size to me. I thought perhaps that they were a different weight (buoyancy), which might affect how quickly they dropped back or something along that line. The carbs I had were of unknown origin, so whether they were rebuilt correctly in the past or not I don't know. I set the float level to an inch and 9/32 (if my memory serves), but someone in a previous post was suggesting that the specs provided were more ballpark then reality. I think I'll switch out the points and take a shot at timing it with a vacuum gauge...maybe that will help fine tune things a bit.
As for the wife...She tolerates my eccentricities and my occasional uprisings.

-Chris

I just disassembled my Rochester B this afternoon ( my first carb adventure) the motor it’s on is 62 235 the year of the carb?? But it pretty much matches the diagram in my 48-51 shop manual . there are 3 ball bearings not counting the one in the pump plunger assy.
One in the power valve assy. (steel) One in the pump discharge 3/16 steel , and one in the pump check 5/32 aluminum.
I am amazed that the truck even ran the amount of crud in the carb was impressive , the hole that feeds the accelerator pump was missing it’s screen and completely filled in , Ha no wonder it was sluggish when it accelerated , it will be interesting to see how it runs when I get it rebuilt

I've only got two, unless I missed one somewhere...
http://www.elltel.net/cdsjohnson/carbdig.htm
the largest being the pump discharge and the second, which looks to be aluminum, in the power valve. No screen on my model (no numbers that I could find on the housing either). Anyway...I'd still be intrested in knowing if the other steel ball in the kit (5/32) should be in the power valve instead.

btw..good to see yet another WA bolter!
-Chris

Ha , they made quite a few different variations of the Rochester B , here is the link to the 48-51 online chevy manuals http://chevy.tocmp.com/1948_51truckshop/51ctsm0663.htm
That’s what my carb looks like , the ball labeled 37 is the one your diagram doesn’t show . do you need it I haven’t a clue .
Btw. Ellensburg is a great place to live . I grew up there and my folks and brother are still there
Brice Erickson 52 3600
http://www.stovebolt.com/gallery/erickson_brice_1952.html

The ball 37 is to keep fuel from going back to the fuel resevor when the pump is acvtivated. It gos under the spring.Insure that the seat is clean and smoth as not to allow flow back to reservor.The ball is a must.

If you have a later Model B, lets say a 55, the picture does not have the aluminum ball 37.

Here is a link http://chevy.tocmp.com/1955truck2shop/55ctsm06m06.htm

So if I read it right, the large steel ball, 3/16, goes in the pump discharge cavity with the bronze spring and the other steel ball goes in the main well support for the power piston.

The aluminum ball must be for the earlier model B only.

Well I know what I'll be doing tomorrow. My air horn is coming off because I have the later model B, and I put the aluminum ball in the main well for the power piston. I guess it makes a difference.

Crud. I put the aluminum 5/32 ball in the power valve assembly. The B I referenced must have been incorrectly rebuilt in the past. I guess it makes sense given that the power piston is pressing against it constantly. Aluminum probably wouldn't hold up over time.
As for ball number 37…In reading the manual, I agree that it seems very necessary during acceleration. Guess I'll throw that puppy in there as well. Worst that can happen, is that it won't run at all. Well, at least it’s not rocket science. Thanks for taking the time to post the diagrams. One of these days I need to pony up and buy a manual.
And Brice, you’re right, Ellensburg is a great little town. I was raised here and chose to have my family here as well. Are you relation to the Smith-Kem clan?
-Chris.

I wonder why they changed the design in 55 and stopped putting the ball in the pump check ? or is it just a mistake on the diagram ? or are the diameter of the passages and hole sizes different enough to make the pump check unnecessary ? (idle curiosity on my part )
And Chris, I am no relation to the smith-kems , however I think you where one year ahead of me in school , I graduated from EHS in 88 , I was the nut who rode my bicycle everywhere and worked at the bicycle shop.

Ha, I just did some more deep cleaning on my carb and lo and behold my the intake to the accelerator pump had the casting but no passage and sure enough that’s the way it is suppose to be. the gas comes in thorough the accelerator pump , Ha the person who had rebuilt it had put the check balls in it , they do nothing !! my carb must be a 55 or later
Here is the cross section link to 55 online chevy manual the description of the accelerator pump is enlightening . http://chevy.tocmp.com/1955truck2shop/55ctsm06m02.htm
Thanks Chis for your timely post
Brice

One way to tell the difference between the earlier and later model B.

Look inside past the choke about half way down, there is a cross bar. The earlier model B has 3 holes in the center area of the crossbar, one of them looks like a rivet.

The later model B only has two holes, no rivet.

After a day of framing in a new closet, and hanging cabinets (honey do list) I'm really looking forward to solving the early-late model B mystery. I plan on ripping into it tomorrow morning if the wind dies down to less than 35mph.
Thanks for the tip Oilrag. I'll give the crossbar a look.
Brice..Yes, graduated in 87, but I don’t remember a nut on a bicycle...except for the guy that used to pedal around town in the clown suit blowing bubbles.
If you and your bolt ever make it as far as Eburg, you should drop by and kick tires.
-Chris.

Alright,
Tore off the B and it turns out (thanks Oilrag) that my carb is the later model, and does not have the check valve in the pump assembly. It would be interesting to know just when Rochester discontinued that feature. Pics here:
http://www.elltel.net/cdsjohnson/latemodelb.htm
I changed the points, condenser and plugs, then timed it with a vacuum gauge. The best reading I could get was between 18 and 19 psi, up from 15 at the old timing. Now it starts great and runs strong, but still hesitates a bit if the throttle is opened to quickly. I guess I may need to tinker with the timing a bit more.
-Chris.

Did you set the idle adjusting needle to the best idle and/or the highest steady vacuum? The needle adjustment is very sensitive, even at 1/16 of a turn, so only turn it a little at a time.

Also a good test - turn the needle in far enough, if everything is working fine, it should shut down the engine.(only ever lightly seat)

What brand & number are the spark plugs?

Here is the Model B spec sheet for 53-55.
http://chevy.tocmp.com/Rochester/9C305p01.htm

Notice the std. metering jet was a #58. Should be stamped on yours.