Rochester B

[thelawdoc]

Originally Posted by bloody hammer

I think I got it straightened out. I set the float lower and put a double gasket between the air horn and the bowl. It no longer leaks from the throttle shaft at the bottom or from between the air horn and bowl towards the top. I do not know WHICH of these things stopped the leaking... maybe both. Either way... there's no more leaking (for now).

Bloody Hammer, how is your Roch B working out? I noticed that you got your rebuild kit from Mike's. I just ordered mine from him. He called me and gave me a lot of time on the phone as we ascertained the precise parts that my version of the B needs. He impressed me as knowing what he talks about. He advises against doubling the gasket because it puts something out of kilter -I don't recall his reason exactly. How did you remedy your leak at the throttle shaft? New Bushing? Or did you change the throttle shaft?

My Roch B seems to be an oddball. For one thing, it has stamping on it of "BC" which should mean that it has something other than manual choke. But all I have is manual choke. Then, whoever did the last rebuild of this carb put on a main gasket that did not have a hole where the carb has a hole. Also, the sintered bronze bearing was missing. Maybe all this is why I was getting bad mpg. We shall see. I have a stock 250. How is your mpg now?
-Alden

[thelawdoc]

That should be sintered bronze filter -not bearing. I was thinking of my Atlas lathe, lol.

[bloody hammer]

Originally Posted by thelawdoc

Bloody Hammer, how is your Roch B working out? I noticed that you got your rebuild kit from Mike's. I just ordered mine from him. He called me and gave me a lot of time on the phone as we ascertained the precise parts that my version of the B needs. He impressed me as knowing what he talks about. He advises against doubling the gasket because it puts something out of kilter -I don't recall his reason exactly. How did you remedy your leak at the throttle shaft? New Bushing? Or did you change the throttle shaft?

My Roch B seems to be an oddball. For one thing, it has stamping on it of "BC" which should mean that it has something other than manual choke. But all I have is manual choke. Then, whoever did the last rebuild of this carb put on a main gasket that did not have a hole where the carb has a hole. Also, the sintered bronze bearing was missing. Maybe all this is why I was getting bad mpg. We shall see. I have a stock 250. How is your mpg now?
-Alden

Alden,

The throttle shaft stopped leaking after I adjusted the float down some. I think the problem was simply too much fuel.

I still have some leaking between the air horn and bowl but with the double gasket it's more of a slow seeping than full-on leak. I know it's not a good long term solution but for now I'm leaving it be.

That's odd that yours is stamped "BC" yet has the manual choke. Maybe someone pieced it together from different carbs?

There's something odd about mine as well... it's stamped with a "C" but as far as I know there is no such thing as a Rochester C (upper left corner). Is that the same place yours is stamped "BC"?

[thelawdoc]

Bloody hammer, You have given me an idea- Perhaps the 'C' that we each have is not intended to refer to a Roch BC. (There is, in fact, a Roch BC.) I have a 'C' in the same spot as you, plus I have 'BCxxxxx' stamped on the choke bracket. When I spoke to Mike, he thought that is my model number, but was confounded when he looked it up and it did not come back as any model number. I have another stamped number that begins with the digits 700 and has no letters, which he thought should be the model number but which also turned out absent from any database. So it is a mystery. Anyway, I ended up photographing each of the many parts, large and small, and after he looked at my parts, it was clear that I have a Roch B. As far as my carb being of various carb parts, I would not be surprised. I think most of my truck came about after someone had a stroll in a scrap yard! As for the double gasket fix, I was surprised that he recommended against it, saying (if I recall correctly) that it might change some mfr spec. In my admittedly layman's mind, it seems to be a rather small increase of volume, in what is mostly an air chamber. Fortunately for me, with my carb there is no perceptible warping of the mating parts, so I do not have to test the admonition on my own skin. (I did not check it with a dial indicator though.) I figure if I run into this issue, I can either sand the top edge on a flat table or double the gasket. I know that a lot of guys will apply various adhesives, but that scares me. I do not even use teflon tape on gas lines anymore because I saw one example of some of the teflon ending up at the needle valve. They say better to use liquid teflon. I did not even know there was such a thing as liquid teflon. So I ended up spending more of my weekend identifying my carb than actually cleaning it. I also found a flour-like whitish powder in the air horn. I feel sure that this is related to corrosion of the zinc alloy used to make these carbs. Maybe Zamak or such. With time, whatever protective layer the factory applies to the carb wears off. There is really not much that we can do as enthusiasts to reinstate such protection. So with time, that zinc alloy is going to exhibit such corrosion. I do not see it being catastrophic and I am not going to send my carb out for plating. But I am mindful to clean it out anytime I tear down the carb. Seems to me it can certainly accumulate at the needle. As far as painting the carb, I can see no reason not to paint the outside. Modern paints are beginning to hold up better and better to gasoline. Not perfectly, but decently. I do not like a rusty or corroded appearance. But a leaky carb bugs me. I have spent hours researching this. Thus far, my suspicion lies with the fuel pump, i.e., that the mechanical fuel pump is either stronger than we might realize, or it becomes too strong if no sintered bronze filter is in place at the carb. Once I have my carb back together I will be paying close attention to this issue. It bothers me to have to accept that the Roch B is simply a leaky carb. It wasn't leaking when it left the Chevy factory. I hear of others getting really nice mpg with inline six and Roch B. I am envious. -Alden

[three80three]

Hey I got a question on a holley 650 double pumper on my truck I drove around all day yesterday and the truck road perfect the next day I go to crank it and it won't stay started I looked in the carb and noticed it was loading up on me but didn't realize that I had a very bad vacum leak I was wondering if that vacum leak would cause my carb to do that?

[thelawdoc]

three80three, vacuum leaks are the bogeyman. They are responsible for most of the evil in this world.

[three80three]

So really there is nothing wrong with the carb huh? It was really that vacum messing me up because I put a quadrajet on and it ran fine one I fixed the vacum problem so do u oh think I should put the holley back on ?

[thelawdoc]

three80three, this forum has veritable experts on the Holley, Quadrajet, etc. and regrettably I am not one of them. I am not an expert at anything. My Rochester B is all that I can handle! But I can tell you what you already know, i.e., if you have a 'major' vacuum leak, you can expect a steady stream of issues. As for the Holley, if you already took it off, you might want to bring it into the house, find a nice quiet corner, disassemble it and give it one good looking over with good light and magnification if you need it. Clean it and when you think it is clean, clean it again. Especially the tiny holes in the jets that do not clear out easily if clogged. Some of the obscure nooks and crannies in carbs can be tedious to clean and you have to be very careful about what you poke into the tiny fuel holes -you can enlarge them in brass fittings rather easily. My point being that if one carb worked and other doesn't, chances are something is gumming up the one that won't carb. Carbs are pretty complex. Everything has to be right if they are to give you their best service. Look for the varnish. Look for hardened carbon. Redo adjustments from scratch. You know all this. Then, once you know that the carb is at spec from every angle, you go on to the next part in the fuel/spark delivery chain. It's a machine. Ghosts do not haunt machines. A vacuum gauge, fuel pressure gauge, and timing light should be pretty much all you need. Wish I could be of more help.

[thelawdoc]

Bloodyhammer, I was looking again at the photo you posted of your rebuild in your initial post. It appears to me that the gasket you put on between the airhorn and float bowl is a thicker, rich-black colored one than the one I have in my kit for my Roch B. Mine seems thinner and is grayish-colored. (Did you perhaps spray silicone on yours?) I have not found anywhere in my research any published specs for the thickness of this gasket. Not in the service manual. Not in rebuild kits. Not on forums. I am curious, since we both have the same carb and we both have rebuild kits from the same source. As for the leaking you had seen from the throttle shaft (which you say has since ceased), is there any particular reason you are not putting a new bushing in there? It seems to be a rather painless procedure based on the adverts for the necessary kit.

Sorry to bombard you with questions. I am in the midst of rebuilding my Roch B. While there is plenty of info and videos online, and ample attention given this carb in the service manual, I have been unable to find any specification for the thickness of the gaskets. As for the specifications/tolerances of the throttle shaft, I have also found nothing, though one can simply check for side-to-side movement of the shaft within its bushing. Ok, hope to hear that your carb is now healthy and happy. -Alden

[bloody hammer]

Originally Posted by thelawdoc

Bloodyhammer, I was looking again at the photo you posted of your rebuild in your initial post. It appears to me that the gasket you put on between the airhorn and float bowl is a thicker, rich-black colored one than the one I have in my kit for my Roch B. Mine seems thinner and is grayish-colored. (Did you perhaps spray silicone on yours?) I have not found anywhere in my research any published specs for the thickness of this gasket. Not in the service manual. Not in rebuild kits. Not on forums. I am curious, since we both have the same carb and we both have rebuild kits from the same source. As for the leaking you had seen from the throttle shaft (which you say has since ceased), is there any particular reason you are not putting a new bushing in there? It seems to be a rather painless procedure based on the adverts for the necessary kit.

Sorry to bombard you with questions. I am in the midst of rebuilding my Roch B. While there is plenty of info and videos online, and ample attention given this carb in the service manual, I have been unable to find any specification for the thickness of the gaskets. As for the specifications/tolerances of the throttle shaft, I have also found nothing, though one can simply check for side-to-side movement of the shaft within its bushing. Ok, hope to hear that your carb is now healthy and happy. -Alden

Alden,

The photo you're looking at must be of when I doubled up the gasket between the air horn and float bowl. It's not just one extra thick gasket.

I agree the throttle shaft bushing fix seems easy enough to do but once the leaking stopped... I had no need to fix it.


I went ahead and ordered a rebuilt Rochester B from RockAuto and it arrived yesterday. Funny enough... it has a doubled gasket and a bushing at the throttle shaft. Hahahaa..... I guess that's how common these issues are with these carbs.

I think I will eventually get a new intake manifold and put on both of these carbs.... even though a lot of folks seem to say it's best to toss the Rochester carbs and buy Carter's. For whatever reason I want to keep messing with the ones I have and try to make the best of it.

-Greg

[thelawdoc]

Greg, I am but a grasshopper among the wise and experienced guys found on these forums. But I do beg of you that you allow such doubling of the gasket to be only a temporary fix. Thicker/doubled gaskets will take in more seepage as opposed to less. It is the warping of Rochester's cheapy Zamak type castings that is the villian here. There is no permanent solution for this blunder by the otherwise bright engineers who designed these carburetors. I do not believe that even filing the mating surfaces flat will be a permanent solution, since the nature of the casting material means that it will warp again -maybe even more severely. I, personally, do mill it, by hand, but I plan on inspecting it every time I remove and clean my carb, which is frequently. I would venture a guess that given the choice between a skunk and a rat when deciding between thicker/doubled gaskets or milling the mating surfaces, it is better to go with milling/filing. But it is really a toss-up. May the truck gods be with both of us!

I want to just make a quick comment about the gaskets for the throttle body. Find the time to double check whether you have a slotted throttle body. None of the gaskets in Mike's kit appear to me to be appropriate for a slotted throttle body. (I have seen a photo of the elusive gasket published by Rochester some years ago, but I do not know whether there are variations of these gaskets.) We will have to do some modification with exacto blades, or find a vendor who sells these gaskets. My research turns up no one who will sell the gaskets without being given the job of rebuilding your carb. But I believe that we can do up the proper gaskets right on our kitchen table if we have photos of it or the specs -the latter unpublished by anyone as far as I can tell. In a pinch, I think we can wing it without the factory specs, but someone on these forums should have these gaskets and publish high resolution photos of them for the benefit of the community. Another prayer to the truck gods.

Returning to the throttle body shaft: it may seem to be remedied but it is a sly rascal. When you have a chance, see whether you have movement side-to-side. If you do, just make a mental note about it, order the kit or fire up your lathe, and then bush it the next time you are home on a rainy day with nothing better to do. Remember, we are dealing with Zamak here.

I find myself resenting the engineers at Rochester for going with this zinc alloy casting recipe. The industry, by the late fifties and early sixties, knew well of the deficiencies of such castings. The otherwise very bright engineers who knew how to make a simple, effective carburetor for the daily driver obviously bowed to the company stockholders and slipped us a mickey here. It is frustrating. This carb ought properly have been made of steel. Ok, enough ranting by a grasshopper, huh? -Alden

[bloody hammer]

My truck's running great and the carb is not leaking/weeping enough to bother me so I consider it a success for now. But, I do realize it's a temp fix. When it starts leaking again I'll fix it again. If it becomes too much of a hassle I'll start looking into the Carter's people have mentioned. Eventually, I want to run double carbs... be those Rochesters or something else.

For right now I think I'm just going to enjoy driving it around and start thinking about what cosmetic type stuff I want to do.... like pull the bucket seats out, re-carpet, and put the bench seat back in.

Then again.... a brake job wouldn't be a bad idea.

[thelawdoc]

Greg, good to hear she is doing well. I hope to see an update from you sometime. Funny, you are taking out your bucket seat and putting back the bench. I am taking out my bench and putting in buckets. That is what I love about these trucks. You can do what you feel like doing with them. -Alden