The Stovebolt Site Forums The Shop Area Engine Shop Rochester B -- what edition? and other Qs

Happy Holidays fellow gearhead buddies and buddetts

Like many of us, Wintertime is a good time for tweeking ye ole stovebolt.

My little project involves reno'ing a Rochester B carb that I've had lying around for eons.
Currently, there is an Autoline Rebuild sitting on the truck. But it is nearing its end, what with ethanol damage and the usual warpage.
It now runs like crap.

So, I'm now resurrecting the original carb, by boiling it in dish deterent, rinsing and blowdrying.
No, I was not gonna gamble on my marriage by sticking it all in the dishwasher.

Because of my relatively remote location, and the lack of resto parts hereabouts I've decided to try and salvage and refurbish as much of the interior guts as possible.

That includes making a new leather cup for the spade-shaft accelerator pump, and hand cutting gaskets for the bowl/horn/throttle body/manifold -- with the right blankstock and X-acto knife it can be pretty straightforward.

But...and I guess there's always a 'but', I found a note from when this carb was first inspected (by me) years ago.
It says that I may need a new pump, pump return spring and checkball for pump well.

I'm rather doubting the checkball detail, so I am not quite sure it's needed .

Will someone here please be so kind as to look at my photos here and let me know if indeed a ball is needed in the pump well (bowl # 7003913).

You will need a ball, a spring and the T shaped retainer in the hole in the float bowl. Please see the first image below. You will also need a ball, a spring and the retaining plug in the power circuit mast piece...second image below.

Don't mess around making gaskets and accelerator pump cup. These are included in even the most basic rebuild kit. If out of stock, your Victoria auto parts store can usually get one the next day as they are probably in stock on the mainland. Cost of the rebuild kit is less than $40.

Thanks for getting back to me, Jon. I got both of those covered.

Because the accelerator pump both draws in fuel and exits it into the discharge chamber, I guess a ball of (? size) should go there to prevent a closed circuit.

One other issue is I don't have the accelerator pump return spring. The specs call for .6 mm gauge x 11 mm ID x 40 mm length.
I can source a similar spring from a neighbour but the length is only 35 mm. If I stretch it another 5 mm, will it make much of a difference in setup?

I get it -- thanks.
I'm not trying to be cheap.

This will be a replacement carb, and I wanna see if it can be rehabilitated through some homebaking.

Meh, if not then I'll have to make some inquiries and wait while they restock.
It's also a ways from where I am currently.

The pump spring returns the pump, it is not a vacuum operated or calibrated spring, so as long as it does what it needs to with out over stressing anything, it will be OK.

Ok, makes sense.
Howabout the 5/32" checkball at the bottom of the accelerator pump well.

I understand the reasoning for it being aluminum. But good luck finding one nowadays.

Do you think the pump return up will have enough lift to move a steel ball instead?

Basically you have one check ball at the vapor vent (which is in the pump plunger head), one above which is the pump discharge ball (held by the spring and T shaped device--that one is 3/16" diameter and not aluminum) and a third in the power valve (already mentioned). That's pretty much it for balls and if you get a proper rebuilding kit they should be included. When you force the pump plunger downward, the vapor check ball is seated (it goes upward to seat). The pressure of the fuel traveling through the discharge passage pushes up on the pump discharge check ball and allows fuel to pass by it, on through and into the boost venturi part. Usually the ball in the pump head is down. In the down position any vapor in the pump well will go past that ball, into the float bowl and from there out the vent in the air horn.

The two springs used on the pump are calibrated and I'd say both are important...especially the duration spring but also the return spring as they do work together. Hope this helps. Good luck.

Thanks for the explanation, Jon

As for the return spring ..not having a local source for this single rather obscure replacement, can a substitute of a slightly thicker gauge spring be used instead (ie, spec is .025" (.6mm) but increase to next .031" (.8mm) gauge)?

Also, does this spring hit absolute bottom of pump well or is it on the ledge just above the ball on the bottom?

I can't answer because I don't have any Rochester carburetors to look at, however I believe it should stop in the pump well prior to the complete compression of the pump return spring. About the return spring, you might post in the Parts Wanted section of the Swap Meet. I had a box of Rochester parts that I had kept since around 1965 but I sold them here a couple of years ago. Sorry.

I would be hesitant to use a thicker gauge spring since the two work together, but that's just me. My thinking is if more resistance appears on the bottom it will affect how the duration spring does its work. Jon H (CarbKing) can tell you more. As I recall he accepts phone calls on Monday and Tuesday.

Thanks.

Btw, will a Carter YF for a 236 cid also work on a 235 cid?

To answer your question... There is no ball in the accelerator pump well. Only the return spring.
Take some fine grit sandpaper or (recommended) crocus cloth and shine up the cylinder wall of the accelerator pump well. Makes the pump more efficient. Oil the pump leather to make it pliable before installing it.

Beg to differ on this carb, Jethro. There is an aluminum ball in the inlet at the base of the pump. It gets the fuel in from a small screened well in the float bowl next to the pump well.

A Carter YF will work well...especially if it is rebuilt correctly. The only difference might be the engine will run better and leaner. Getting away from warped castings and the Rochester power circuit scheme will be a nice relief. Which YF model were you considering?

Edited to use visible ink.

Grrr. Software problems. Yes, the Carter YF will work fine and will be an improvement over the Rochester.

The carb I am considering is a good deal on a reman single barrel YF (2100) that usually fits a GMC 236 engine in this offering.

I understand that 236 is quite a different beast from the Chev 235, so not sure I could easily adapt the whole carb to the 235.

For instance, how much difference is the mounting flange of 236 manifold vs 235 manifold?
Could it be just a simple re-drill of the holes?

The YF 2100s will work fine and is a very good one for the 235 Chevy. You won’t have to modify anything.

What's the number stamped on the carburetor body? A YF2100 fits on a 235 and would likely fit, but if it's a YF964, that would have a smaller mounting flange and fits on a 216.

Here's a couple of photos of a YF964 showing the model number and the mounting bolt spacing. Note that the gasket has elongated holes that fit either the 964 or 2100 carbs.

QUOTE 55FirstSeries: "The carb I am considering is a good deal on a reman single barrel YF (2100) that usually fits a GMC 236 engine in this offering." END QUOTE

Someone is pulling your leg !

The Carter type YF number 2100s was produced specifically for replacement of the original Rochester on a Chevrolet 235 CID engine within a certain year range. I have zero, at least to my knowledge, factory Carter information that suggested the use of this unit on a 236 GMC engine. If anyone has such information, I would like a copy for my records.

The 236 used Zenith carburetors as original equipment, and while I really like the type YF, in my opinion, the Zenith is superior.

Jon

The carb in question is a Uremco 3-312 https://www.uremcoinc.com/shop/carburetor/uremco-part-no-3-312/

My bad, it's not a 2100

not worth minor-modding the Uremco to run on a later 50's 235 ?

Uremco is re-manufactured Fitzall unit.

Basically they take whatever used parts they have in the barrel and put them together to make a functional carburetor that fits a wide variety of applications rather than for your specific engine.

It will probably work.

So will removing the hood, and hiring a 15-year-old to stand on the running board and pour fuel into the engine from a leaky boot !

How well either works remains to be seen.

I would personally wait for a 2100s.

Jon

So, "remanufactured (reman)" is really just that and not a Rebuild of existing carb, huh

Being Canadian, I am not familiar with Uremco. Autoline remade carbs I've used though -- not bad, but not great either.

Great point, Jon

Yeah, I've been watching for a 2100 core for eons. Near impossible to find here in Canuckland. Except for the Chinese clones, importing quality parts from the US is crazy expensive nowadays, even for just a comprehensive rebuild kit. Local kits are expensive and totally lacking from what they use to include.

Heck, maybe I'll just stick with homebaking my original Rochester B, and perhaps the operating Autoline Rochester B while I'm at it..

In the Tech Tips part of this section (top part of the section), you'll find a two part report I did a few years ago. Hopefully that will help things with the Rochester. I listed a rebuilt Carter YF today in the Swap Meet section. It is the YF788SA model (designed for the 1950-52 235 as I recall. Not a show quality carburetor in any imaginable way...more of a "user" but I expect it will be okay and it does have manual choke and throttle (no mounting hardware but you might be able to adapt a Rochester cable mount to it). Hope it is helpful. Given what Carter YF models for the 235 with a manual choke are selling for, this one is definitely affordable. YF2100s are really hard to find and people have pretty well priced them out of reach. Sadly.

I would avoid any of the Chinese made carburetors. No, the "rebuild mills" are just combining junk into something that might or might not work. More today than ever before I would say. Good luck.

Thanks for your heads-up info and carb offer, Jon.

I think I'll pass on it and try another approach ..if my Roch rebuilding doesn't pan out.

In meantime, I will continue to contribute to this forum

So Jon, I managed to true up a (spare) Roch B carb via both of your Casting Fixes (dewarp) tech tips -- thanks.

However, one thing that stands out may be the omission of whether the choke and throttle plates should be removed prior to putting the works into the BBQ at 400+ deg.

After finishing the process and trying to reassemble the choke plate and shaft I found that the through-openings were slightly warped and thus binding the brass shaft -- they no longer lined up.
I'm still trying to resolve that issue (without reboring) and to make the choke more moveable.

So, on the second (operating) Roch B carb, should I just leave the plate and shaft in-place and heat it all together?

I've done it both ways with no problems. However it is important to remember the metal can be re-shaped by re-heating to 400 degrees. So, in that case I think I would suggest leaving the shaft and plate in place on the second one and on the first one I would re-heat and while it was hot (wearing thick gloves) I would re-insert the shaft and see if I could make it fit correctly. I would not re-bore it. Sorry to hear you had this problem.

Thanks, Jon
I will cook it with the choke shaft in.
And perhaps re-cook the "spare" to see if the choke shaft (by itself without plate) will loosen up.

Another thing I noticed is that the 2 carbs are different in series. The old "spare' has a small screened (inlet) well next to the main accel pump well. And the pump well has 2 bottom holes with a provision for an aluminum check ball in one of the holes (as discussed earlier) -- I like that feature.
As well, the throttle body is a larger bore by about 1/4" (nope, does not match the carb bore)

The other main carb seems newer as it was an Autoline rebuild. It has just one crude side hole in the bottom of the accel pump well.
Also, unlike the "spare" there is no port in the airhorn (just above the discharge hole in the base).
Throttle body is matching at 1.5 in.

Hah... aside from swapping throttle bodies, it would be nice to be able to interchange the upper and lower parts.


Btw, when I tweeked the "spare" via heating, I screwed the carb halves together and they seemed to just meld-to-form! Any slight gaps mostly disappeared.
Although the inlet end is a [censored] to mate properly.
Yup, a rather stupid design!

Please try that. Autoline once was a pretty reliable operation. Friends have told me things have changed there but I don't know about that. I would imagine any rebuilding operation is going to be challenged greatly today.

Here is a link to a paper written by Jon H (CarbKing): https://thecarburetorshop.com/CarterChevroletYF.htm I think it should be interesting to see the changes and compare.

I did notice that the interior of the Autoline example looked as if it was rehabbed by a hammer and chisel.
And the mating edges and raised lines were so etched that they were barely evident anymore.
Whereas my old spare OEM still looked relatively-factory condition.

So, which one to use : "old" OEM version or the "newer" (Autoline Rochester rebuild)?


Thanks for CarbKing's link. Very limited info there for id'ing my Roch carbs. But good info about carbs in general.

There is limited info on IDing Rochester carbs because they ARE SIMPLY NOT WORTH DOING AN EXACT IDENTIFICATION !!! The chart on the website clearly shows many different carbs used the same castings by number.

With few exceptions (the 1949 and 1950 Olds, 1951 Cadillac, and 1955 Olds 2-barrels come to mind) here is the way you identify virtually all Rochester carburetors PRIOR to 1968 once the identification tag has been removed:

(1) Acquire Rochester assembly specifications for all carburetors pre-1968 (good luck, in 51 years I have acquired those from 1949 through 1959 ONLY)
(2) Totally disassemble the Rochester carburetor in question and measure ALL machined surfaces and pressed-in calibrations (idle air-bleed, idle bypass, idle restrictor, etc, etc, etc.).
(3) Compare all measurements sheet by sheet against all of the assembly specification sheets for the type carburetor in question until only one sheet is left.
(4) You have now identified the carburetor.

How much time has been spent ?

And you still have a Rochester B. Now you have to rebuild it.

In 1968, federal smog emissions required the identification number to be stamped on the carburetor.

For those truly in love with the Rochester B (I can understand this for an absolute numbers-matching show vehicle that is never driven), simply do a search on ebay for the one you need WITH an original tag. What is it going to cost ? The shipping charge may be higher than the value of the B.

For those that actually plan on driving their truck, better options exist !

Jon

I don’t know that it’s been done here, but somthing I’ve pondered:

1) Somehow acquire or rebuild a Rochester B to “pristine” condition. Might take a NOS carb (properly freshened up) to achieve the level of pristine I am imagining here.

2) Rebuild a proper YF (let’s just say 2100s for this thought experiment) to similar pristine condition.

3) Run both, on a well-tuned 235 in a functional vehicle, through a series of measurable performance and drivability tests.

Not sure exactly what tests. Some of the performance stuff is easy to set up. The ease of starting, smoothness of acceleration, etc….that would take a bit more thought. An air fuel ratio gauge might be the best tool for some of it.

Overall idea would be to determine just how good a “B” can be at its VERY best compared to a YF. There are many of us (including yours truly) who have been fully converted to the YF fan club based on a before vs after experience. However, I’d say most of us (including yours truly) were starting with a B that suffered from the common “didn’t age well” shortcomings of the Rochester: unknown mishmash of parts, warped castings, etc.

I’m curious how much of the B’s (deserved, IMO) poor reputation can be attributed to THOSE issues vs. engineering flaws that would have been evident day one in 1950 on a brand new carb. (For instance, a bit of an odd power valve setup)

I’m not curious enough to actually try any of this, just thinking out loud.

Nathan - if ENOUGH time is spent on the B, it can get pretty close to the YF.

How much time is enough time ???

In 1995, I did such a test (no, no chassis dyno, no A/F tests, only "seat of the pants" testing on a Chevy Biscayne).

Now, the question is: "how much time is ENOUGH time" ???

The answer: 42 hours of shop time !!!!!

In rural Eldon, Missouri, the CHEAPEST shop time of which I am aware today is $60/hour, most are more than $100.

42 times $60 is $2520. Anyone want to buy a Rochester B for more than $2500 ??? If so, don't call me, today, I don't have 42 hours to waste on a B !

And the kicker is: in 5 years, you get to do about half of that again !!!!!

Jon

I definitely don't disagree with the above opinions.

My truck is just a daily driver (running errands) during the fair-weather months only.
It now resides under cover until the Spring. Hence, time for general maintenance (ie, carb) ..not to mention undoing of ethanol damage.

If I had my drothers, I'd definitely opt for a YF 2100 if it could be found in my locale, or even a rebuilt or rebuildable core imported at a reasonable cost -- there are none.
I'd even look at a Zenith 28 or a Stromberg..

For now, it's having to fashion gaskets and parts from my shop.

And again, the kits hereabouts are now severely lacking (vs the old days), and grossly overpriced at local Napa or FLAPS.
So, as long as I've either got old expired samples or dimensions, it's gonna have to remain somewhat doable.
Yup, it's still a royal PITA though.

Dang jalopies!

Yeah, with today's shortage of quality vintage parts it can become quite the rabbit hole

Here are a few thoughts for you: the Rochester B was designed when real gasoline was used. If that isn't understood and appreciated, I believe it is likely nothing good can come from a Rochester B study. Real gasoline could be left in a can or tank for a much longer time and still be usable because deposits take much longer to form. And (the important part) leaded gas re-introduced to the carburetor will in time dissolve any deposits left whereas unleaded gas won't. Unleaded gas (even if it has no ethanol) will begin to get gummy after a few weeks. A friend (a retired petroleum engineer) told me this is because the "light" components evaporate very rapidly (and naturally evaporate first) and leave the "heavy" components which according to him quickly start becoming varnish which will not be dissolved with unleaded gasoline because fundamentally while you are waiting for the gum to be dissolved the "new" unleaded gas is rapidly deteriorating in the same fashion. So you're chasing your tail. His suggestion was "if you're going to use it, don't wait at all." He further said there is no reason whatever to leave an air space in your gas tank if you are not driving your vehicle regularly. He said ethanol gas can begin going bad in as few as 10 days (especially in the summer). Ethanol by the way is added at the time the gas is being distributed...as close to the time of sale as is possible. For good reason. While doing all the work on the Rochester B I took three vials of unleaded ethanol gas (each bought apx 1 week apart) and watched them. They were stored with the lids closed but with a space of air above them of about 2 or 3 inches. Every one of them started changing color in a few days. You can see them down below. In a month or so the first one i bought when poured into a metal cup and lit burned with a very heavy black smoke and left a gummy and tarry deposit.

So what is my point? Simply this: The power piston (in my opinion one of a few different Achille's Heels of the Rochester B) is doomed to get stuck and if the truck isn't used pretty frequently it could be only a couple of weeks of inactivity before it begins sticking. Of the five carburetors I broke down and studied, four had seriously stuck power pistons. They would not move at all. One didn't and it was because it had been sold as rebuilt by Autoline several years prior and had never been used. It had been wrapped in bubble wrap and left in a closet. I should mention the castings were warped but the exterior looked good. Every single power piston gets stuck in the "DOWN" position (meaning the carburetor is doomed to run as rich as possible at that point). I should add I tried every possible thing I could think of to keep the power piston dry. I tried making a rubber nipple, I installed viton o-rings and even tried making a nylon spacer. No luck at all. No matter what I did, I could not keep gasoline out of there.

I did try to find an NOS Rochester B at that time (I watched over several months, actually). I could never find one, although 2 or 3 years later I remember Jon H told me he found one in his shop. Every time I found one listed as NOS the seller could never prove it and there was never a tag on it and it looked more like pixie dust than truth. So, maybe there is one out there but I agree with Jon H. A lot of work to maybe go nowhere.

I am totally satisfied to know that someone, at some point, did the work. 1995 wasn’t exactly yesterday, but would love to read some of what you recall from that “seat of the pants” work.

My reason for even thinking about such an experiment was to just put to bed the idea that the effort to properly restore a B was worthwhile.

That said, I can understand and appreciate what the OP is going through trying to keep a truck on the road. The 235-sized, manual choke, YF’s are getting pretty darn scarce. If the OP is willing to consider an auto choke carb, there are all kinds of possibilities we could discuss. Even outside the YF family.

Side note - I recently acquired a 235-spec Stromberg BXVD-3 after a year or more of looking for one at a price I was willing to pay. It’s a side project thing at best, but once I get it rebuilt, I do want to do some “seat of the pants” comparison to my 2100s. Not that I have any complaints whatsoever, just trying to learn a different carb and to share those leanings. The Strombergs aren’t discussed often here.

Those were very interesting observations, Jon.

After yanking my 2 carbs apart, both power pistons look almost new with nary an gum or debris anywhere. Where I normally find annual wear is in the internal body of the carbs, rubber hoses, fuel pump, etc.

For some years now I have regularly used Star Tron additive in the fuel. It has helped with phase separation while seemingly maintaining the (ethanol) fuel quality.
In fact, I double dose the tank just before filling with Premium (still E10 nowadays), and after 4 months under cover -- with the monthly startups -- it starts and runs passably until the first fill in the Spring.
So yeah, I'm a believer and think Star Tron does work as advertised.
But, it doesn't get rid of the alcohol per se and that stuff plays havoc on the rest of the fuel system.

I also have a few jugs of lead additive left over from the early 80s. Donno if that too would help in these matters.

My main beef is with the quality of the GM Rochester B. As simple of a device that it appears to be, it really lacks in engineering quality.
Hence, my former search for something more reliable and with better performance -- something I don't wanna keep screwing around with.
However, on the other side of this coin the Winter months do give me some time to play with this ole truck, huh...