The Stovebolt Site Forums The Shop Area Engine Shop Rochester "B" carb questions, just a few!

Just putting the finishing touches on my 216 valve job. Rebuilt the distributor, radiators back from radiator shop, new oil feed lines to the rockers, in short, everything else I could unbolt from the short block has been redone. The last item on the list is my GM model “B”, pn.7002050, Rochester carb. Before I shut her down because of a burnt valve, I noticed that the idle screw had no affect on the way the engine ran. I could screw it in all the way and it still idled just fine and on the road it ran amazingly well. So I tore into it yesterday to find out what was going on, also just to make sure everything else was ok. Well it twasn’t!!!

The shotglass full of very fine “rust dust” wasn’t too much of a surprise since the only filter was the wire screen in the fuel pump which by the way was also loaded with residue. Inside there were a few things that didn’t match up with the manuals and I would like to hear from you carburetor experts out there.

The first thing I notice right off the bat was a rattle in one of the floats or should I say a splash when I shook it. Yep, a tiny leak, in the center of the bead, on the inside of one of the floats. I’m sure that I can drain it and solder the hole shut but haven’t figured out how to leak check it yet. Ideas???

The second thing doesn’t need explaining but again it surprised me that the engine ran so well. The power piston was stuck solid. I didn’t want to take a chance of bending it so I made a little soft-clamp that I put in the drill press so I would have a straight pull on it. It finally let loose after soaking with some Kroil. Also the spring is stuck in the piston and I don’t want to stretch it out trying to pull it out, as this could change the response of the power piston. Normally I should be able to remove it unless this is something that is different on these carbs. Anyone ran into this??

The third thing was, the screen and retainer in the base of the accelerator pump well was missing. I’m guessing that it might have been left out during a previous rebuild. So I suppose it needs to be replaced. I was going to cut a new one from some fine brass cloth and make a retainer from a coil cut from a tension spring. Anyone found this missing from their carb during rebuild?

The forth item is a little trickier to describe. It’s the “pump discharge spring stop”. In the past all of the carbs that I have rebuilt only used the T’ shaped spring stop that was pressed into the hole and this kit has a new one like I expected.
However, on this carb there is a something called a “pump discharge guide”. This looks like a round plug with a slot cut about 80% of the way through one side and apparently is inserted into the hole and then the slot is expanded. According to the GM “B” manual you should, “rotate it with a thin blade screwdriver until it is free and is pushed up by spring pressure”. No way can I get this to rotate so far. This well is most likely to be full of sediment and I really need to get this plug out to clear it. Any experience with this one?
I’ll stop here and see what ya all got to say this morning.
Denny Graham
Sandwich, IL

Note about old Carb Cleaners: I dipped the air horn and all of the small parts in a gallon of new/fresh Gunk Carb cleaner from Farm and Fleet, worked fine. Out of curiosity I soaked the throttle body and bowl in my 20-year-old gallon of Gunk Carb cleaner and it still stripped everything just fine. Long ago it had eaten through the original can, then every few years it would eat thorough the plastic jugs but the HDPE jug its in now seems to be holding it OK.

The way to check a brass float is to hold it under clear water, no bubbles=good float. I've had good luck w/polishing the power piston using 000 steel wool, seems on mine clean just wasn't enough. Brian

Hey 64fleetside don't mean to step on your toes. Thats hot water we use, it will expand the ambient air in the float. Denny enjoy reading your posts wish you were working on a 63 or better C20.

Larry

Fisrt thing is first. Make sure everything is clean without any sediment or any deposits. To get an old carb apart and get all the pieces out might require a little bit of force but not too much becuse you dont want to break it. to get the little T dischrage spring out use either side cutters or needle nose pliers to pull it out dont worry about damaging it becuase you should have a new one in your rebuild kit. the power valve soak it carb cleaner and the spring should come out, if carb cleaner use some deep penetrating oil or whatver stuff you like. i had a lot of luck cleaning carb parts with 2000 grit wet/dry automotive sand paper and a litle bit of engine oil. dont soak the snad paper in oil just dab it lightly and it worked great on my power valve cleaned it right up without cratching. afterwords you can use some carb cleaner or dgreaser to get rid of the engine oil. GET A NEW FLOAT or at least have a good fire extinguisehr handy i think that you can get them for like 10$ at the fillingstation.com. bceause even if you solder it the weight will be off and you will have a very hard time setting the correct float level for your truck to run fine without floading or percolating when you turn it off. The screen get a piece of springy steal and form it into a "C" shape slightly larger then the opening so that when you put it in it will act like a spring and hold the mesh in place.

good luck and be careful if you choose to solder the float

if you have any questions ask away

chaimv

Denny - below is an excerpt from our website on the testing and repair of brass floats.

Generally a good idea to order the rebuilding kit FIRST; then you know which parts you can destroy in the rebuilding process. Both the discharge valve and the vacuum spring are in the better kits.

Jon.

BRASS FLOATS

Many mechanics have been conditioned to ask for a float each time they rebuild a carburetor, due to the reasonable price of modern, mass-produced floats, and the propensity of nitrophyl (foam) floats to absorb gasoline after time. In dealing with older, NON-CURRENT-PRODUCTION brass floats, neither of the above are true, and a mechanic should attempt to 'save' the float if at all possible.

The first step is to clean the float and inspect it for obvious damage. Small dings and dents are quite common, even in unused floats, and occurred when the manufacturer shipped the floats in bulk. Major dents (generally caused by water freezing in the carburetor) are not generally repairable. If one can hear liquid sloshing around inside the float, skip to the next paragraph. If the float looks to be reasonably damage-free, it should be tested. Testing is accomplished by grasping the float arm with a pair of needle-nose pliers, and submerging the float in very hot water. The hot water will pressurize the air inside the float, and a leaky float will blow a stream of bubbles.

If the float should need repair, it is important to understand how the float was originally produced. Virtually all brass float pontoons (the floating part) are composed of two pieces (a few are more) of brass soldered together. The pieces differ in the seam area, as one piece has a male seam and the other a female seam. One float piece will also have a small hole for temperature equilization. This hole will be covered by a small drop of solder, and will be as far from the seam as possible. The manufacturer would solder the two pieces together, allow the float to cool completely, AND THEN close the equilization hole. Soldering MUST be done using a soldering 'iron'. Repair should not be attempted using either a torch, or a soldering gun. If you plan on disregarding this advice, read the next paragraph first! The following procedure works for us (no, we will not repair your float unless we restore the entire carburetor): First, if liquid is present inside the float, find the hole, and remove the liquid by placing the hole down inside the hot water. The pressure will force the liquid from the float. If the float has much liquid, it may be necessary to remove the float from the hot water, allow the float to cool, and repeat the hot water dip. Once the liquid has been removed, and the leak has been marked, open the equilization hole by removing the solder. Solder the leak closed using as little solder as possible. A small piece of tape over the equilization hole will allow the hot water test to be preformed. If there are no leaks, remove the tape, and ALLOW THE FLOAT TO COOL COMPLETELY before closing the equilization hole. A final test, and you have 'saved' a valuable float.

Thanks Jon and Larry for jogging my memory, I remember hot water testing of floats now that you mention it, but it was probably 50 years ago since I had to test one and I'd forgotten bout it.
I’d never tear into a carb without having the new parts around Jon, fact is I've had two kits here for a couple of months cuz I knew I was going to rebuild the carb at some point I just dint know when. My dad was an old school master mechanic and when I was a kid and taught me the right way to rebuild carburetors. Back then the kits used to come with the tapered lead plugs, we would pull the old ones for clear access to the whole passage while in the cleaner. Without pulling them you face the real possibility of an air pocket and cleaner not getting to it. I’ve made up a small plate with a variety of tapered holes that I warm up and pour plugs into. That’s just the way I was taught.
I was an instrument welder/Sr. research tech at a National Accelerator lab here in suburban Chicago and my hobby was restoring antique radios, so I'm familiar and completely at home with all phases of soldering, it was just the leak testing that I’d forgotten about.
Power Piston fits fine after it came out of the cleaner Larry, just a little tooth brushin’, no need for abrasives! I did ask if the spring was pressed into the Pistons on any of these “B” carbs. Seems to me that they were always loose.
Also I thought I clearly described that the “Pump discharge guide” was a round plug not the standard tee stop chaimv. The only place I’ve see this type stop discussed was in the GM “B” manual. Guess no one has run into one of these so I’ll have to wing it. Sorry again but no abrasives on the die-casting, that’s just asking for more oxidation down the line.
Denny Graham
Sandwich, IL

Denny, the early,('50 to sometime in '51) Rochs. used that discharge guide you speak of. They did some redesigns of the carb then, including thicker flanges where the bowl halves come together. I vaguely remember coming across it when I rebuilt one of the old style ones, but it's been a few years and I don't remember exactly what I did.

Bob

Yeah, the water needs to be hot, not boiling but very hot, sorry, had a mind fart.

Your excused Brian, I can understand that. I have the same thing happening to me, I remembered the hot water test after Jon jogged my mammary.
Thanks Bob, I knew someone must have run across this brass plug stop before. I, first time I’d seen it, even though in my younger days I’d rebuilt quite a few Chevy 6’s and I was a parts man for Chevy for almost six years.
To get it out I just took a very small center punch and collapsed the two sides into the slot and it popped right out from the discharge spring pressure. The kits always have the tee stops in them but I’m going to duplicate the brass stop that came out of it. I’ll spin one up on the lathe in the morning. Just like I suspected, the well was full of crud. Now that all the plugs are out of the casting I’ll dip it for a couple more hours in the morning.
Denny Graham
Sandwich, IL

Denny - you are correct that spinning a brass stop on the lathe is fairly simple. The cheap, generic kits do come with the "T" stop, but the better kits do come with the brass stop.

Jon.

Thanks Jon, job is finished. Who'd ever thought this simple rebuild would take a couple of days! There was a bunch wrong with this “B” so I guess that was why. Where are you finding the “better kits”???

The previous rebuild was done pretty half-assed, they used the wrong are horn gasket and the Main well housing was sitting half on half off and was cocked to one side. Besides the Power piston being frozen in the air horn well it now lines up with port in the main well housing, as it should.
I took all the measurements off the old discharge stop and drew it up in the CAD then spun a few extras down on the lathe for future use. Since the old needle had a nice groove crushed into it I drew that up also and made up a few of them too.
Using my hydraulic press I punched out a bunch of 3/8" screens from woven Brass Mesh (60 mesh) for the pump screen. Then back in the lathe I wound a bunch of 3/8" spring clips from .030" spring wire stock.
The retaining screw (10-32) for the Fast Idle Lever was cross threaded when I took it apart, and I lucked out there, I chased the threads with a bottom tap and put the screw in straight, it seems ok now.
The one float did have a small pinhole in the rib on the inside, thanks for the heads up bout the hot water test. As a precaution I wrapped a strip of copper around the circumference as a heat sink just to make sure I dint disturb the seam or mounting joints. After a good cleaning I’s ready for the plug. My Weller pencil iron wasn’t enough so I got out the big guns (and I don’t mean the soldering guns), a 100w iron I use for chassis grounds in my radio work. Just a touch with it and I had a dot of well-bonded rosin cored solder over the leak.
So, new fillister head screws, new brass inlet and vacuum fittings to top things off and we’re looking like a brandy new carb again. Gonna add an AC gas filter just before the carb inlet this time also.

If I recall correctly Jon, I believe you said something to the affect that the Rochester’s were junk, switch to a Carter! I can understand why now. The one thing that I found wrong with this carb that I can’t fix, was the gasket surface at the front of the float bowl opposite the linkage. It was low by a good .020”. This came from the factory like this because there is no way the bowl could warp like this in use, It’s not the cover it’s the bowl. I have some serious doubts whether the gasket will seal at this point. It wont cause an air leak simply a fuel leak. If I do have a problem with it, the only fix I can think of is to cut another gasket from thicker material. That should be fun! Although I am not aware of it but I would bet there was a bulletin issued to the dealers on this one.
Just exactly how does the CarbKing deal with these carbs when he runs into them???
Denny Graham
Sandwich, IL

Denny - both the bowl and the airhorn warp. Do a search on this forum, as I have explained in detail how to straighten the castings.

And anymore, carbking (small "c", not large) doesn't deal with them. The Rochester B is one of a few types of carburetors we simply refuse to restore.

Jon.

That's what I thought you had said. I'll do some more searching and see if I can find your past posts. Airhorn is flat to with in a couple of mils, it's all in the bowl on this one.
Tks
Denny G

Well Jon, I spent about 3 hours searching last night, "Rochester", "Rochester B", "Rochester carb", "Rochester warp", “Rochester float bowl”, Rochester airhorn”, “Rochester rebuild”, “Rochester repair”, "carbking", "carburetor", and read thru nearly 500 hits. So ya can’t say that I didn’t try!

I only found one (1) post that referred to a fix for the warped castings, and it simply said, “ make a fixture to hold the casting and bake it at 400° for an hour.” Seems like a rather vague description of the fixture and procedure. It appears that I still haven’t found the elusive solution, I’m sure from what you have been saying that you have written more on the subject but I can’t for the life of me find it!

Also you refer repeatedly to “the better kits”. Just exactly what do you mean by the “better kits” and again, who is the one that is selling these “better kits”. I believe that I made reference to kits that I used when I was a kid back in the 50’s, that came with lo & hi speed needles, lead plugs so you could clean ALL the drilled passages and a few even came with a new float where that was a common problem. I’m sure that these kinds of kits are long gone but if there is a better line of kits available please let us in on the secret.

I’m certainly not an expert on carburetors and I just want to get a clear picture in my mind, so that is why I am seeking your opinions. I’m not exactly sure yet why you have such a strong aversion to the Rochester Carburetor, other than it is only held together with four screws, which certainly seems to be a weak spot. Other than that it seems like a pretty simple straight forward metering devise that, if restored properly should give good service, there are millions of them out there that have been in operation for decades. Even with all the things that were wrong with the “B” that was on my truck, it still ran amazingly well. The engine started and accelerated just fine and I was surprised to find the problems that I did when I tore it apart.
Granted from a performance standpoint there are many carburetors out there that are far superior to the Rochester “B”, but if someone is performing an accurate restoration I would think they would want to keep the original fuel system intact.
Thanks for you opinions,
Denny Graham
Sandwich, IL

Denny, here's the process described by carbking in more detail. I don't know if it's in the archives or not. I saved it to a text file a long time ago.

Ok Larry, thanks I didn't see that one last night. sounds simple enough. I even have a heat treat oven so I won't have to bother with "my big old wife's" oven.
I'm looking at the melting point of Zinc (419.53 °C or 787.15 °F) and wondering if there would be any distortion from doing this. Also am wondering at what temperature the Zinc institute says would nominally cause the material to yield.
I can’t understand why the castings would change shape over time. Plastics change shape over time because they continually out gas over their life time, they eventually dry out causing them to shrink. Metals on the other hand, including Zinc alloys don’t out gas like plastics so I don’t see what would cause them to warp. The heat at the carburetor simply isn’t enough to relax the material.
I may be wrong, but I can’t help but think that these castings came from the factory already warped.

Back in the 20’s there were problems with some Zinc (aka: pot metal) castings growing. Many of the antique radios from the 20’s suffer from this ailment. The problem took place in between the grain boundaries and caused the casting to expand, but it was discovered that the addition of certain alloys were what caused it and after that the metals industry was well aware of the problem. This was very early in the 30’s and certainly after WWII and into the 50’s they had it well in hand.

I wish I had some castings to experiment with, I have a machine shop so I can make the fixtures with no problem.
Interesting problem, If I’m gonna keep working on these till I’m 100 I’d like to understand it better.
Denny Graham
Sandwich, IL