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

Well I had some spare time today so I dismanteled
the carb for my 261..... now I am stumped.....

Everything checked alreight except for the accelarator pump shaft. In the carb... and the two spare 235 models I checked out.... the shaft for the pump is flat with a slit in the top end for the linkage to fit in against the spring....

...but darnit in the kit the accel. pump shaft is round with a groove at the upper end that would take a clip of some sort.....

Whaw I do now Bossman????

I even checked the parts GM book for the 1958 model year.... the picture shows ONLY the flat shafted plunger rod.....

Would sure appreciate getting back some comments on my problem.....

CarbKing can I draw on your vast experience... my kit box says it fits a Chev 57 to 62 pass. car... is mine different because it came from a 261 truck engine....?? or do you have the right parts in your carb kits.....if so consider one sold to me......

It's always the little things that screws you up....

Bob C.

You have experienced one of the many problems with the pre-1967 Rochester carburetors. Prior to 1967, Rochester carburetors were identified ONLY by tag. As the commercial carburetor rebuilders "group" carburetors of different years and applications into a common group, they remove the tag such that the customer has no idea which carburetor was sold to them.

As to your specific problem: Rochester used many DIFFERENT accelerator pumps in the type B carbs over the years. These vary in design (flat, and round) length, and material (leather, and neopreme - leather is much superior). I have not seen a variance in diameter, but I wouldn't bet against it.

Jon.

Sometimes you can take the pump material out of
one & put it in the old one.

Thanks for the insight Jon....... any suggestions ...hint hint.. nudge nudge.... as to were I can find the right carb kit...????

Interesthing suggestions on changing the piston part at the bottom...... I have micked the shaft where the piston cup is fittend and both are the same diameter... one continues round all the way up the other .. the old one....is crimped on the flat section. That piston part seems to be segmented in 4 pieces to allow some flex when installed on the shaft.... the big question is...... and maybe Carbking can chip in..... can they be removed without breaking the white metal part of the piston cup...????? at worst I will slowly grind the rod on the good piston to remove the good leather skirt and reverse the process on the old one... grind the white metal and save the round rod and try to re-instal........ I much prefer to working on larger things with a bigger hammer!!!!

One more question..... I soaked the carb in Keel-Flo carb cleaner for 24 hours..... rinsed in boiling hot water.... blown dry..... I still have some white powder residue inside the walls of the bowl.... and inside the accelarator pump well....

Is this normal..... Whaw da doo wrong this time...??? I am thinking of trying to polish with a felt bob or fine brass wire wheel
mounted in the Dremel tool and rewash if necessary..... what is that powder???
...must it be all removed????

Just think ,if I keep this up, I will be smart like you guys some day!!!!!

Sure appreciate your help..... it not like I can talk about this with the wife......hahaha

Bob C.

Bob - Yes, I know where you can get the proper kit, if you have the tag number of your present carburetor. You have found one of the reasons why we started producing kits years ago, when we were doing restorations only, and getting incorrect parts at the parts stores. The correct pump for the 1958 261 is part number 7002091 and has the flat shaft.

Accelerator pumps come with both neopreme and leather cups (the leather is MUCH superior, but the neopreme is MUCH cheaper).

Often the neopreme cup can be easily removed from one pump and placed on another. Check the diameter of the "thimble" holding the pump.

The leather pump is more difficult to transfer, but it can be done. To do so, very carefully grind off the peened ends of both pumps; and remove the thimble assemble (thimble, leather cup, and expander spring). Now mill approximately 0.050 (50 thousandths) from the thimble stop on the shaft of the old pump. Assemble the new leather cup and spring with the old thimble back on the old pump. The 0.050 will allow you to repeen the shaft over the thimble. The pump should not be 0.050 shorter. This will cause a slightly larger shot of gasoline when the pump is used, and can slightly impact your fuel economy in city driving.

It might be easier to acquire a "junk" Rochester with the plunger for the round shaft, and switch them.

Jon.

Thanks Jon......

Now I know what I am doing Sunday afternoon.....

I will try to transfer the piton cup assembly form the new round shaft to the old flat shaft...what have I got to loose.

Oddly enough... of the 4 Rochester I curently have all of them are flat shaft....my luck....

If I mess up I will look you up on the link and order a new kit.....

Am I correct in buffing out the whitish deposit left in the carb after the soaking in carb cleaner....??? I am particularly concerned with the deposit left insode the accelarator pump well as it might affect the overall performance.

Fuel consumption wise I do not expect much from my old truck.... with 6.39 axles and a top speed of 50mph + - it is not going to win any economy run..... I will be please if it runs good!!!!

With more practical experience, I may decide to trailer it to remote military shows due to the distance...... but it will be nice to see the heads turn when I drive it around town.....

Thanks for your help.....

Bob C.

The "whitish deposit" is corrosion. Yes, you should make an attempt to remove it. Perhaps someone with more training in chemistry than I will chime in here; but in essence, a carburetor is a classic example of a Galvanic cell (battery), composed of two (in this case more) dissimiliar metals in the presence of a liquid. I have forgotten the correct terms, but the issue has to do with the bonding capabilities of the metals. The corrosion is the result of electron flow, where particles from one metal (in this case the zinc) are transferred to the new substance (the whitish deposits). Electroplating is a simply a controlled version of this issue.

After the zinc alloy carburetor bodies were cast, they were dipped in a "chromate solution" which (unlike the "paint" currently being sold to hobbyists) placed a protective coating on the zinc alloy. Eventually, the protective coating will wear off, and corrosion will begin. If the protective coating is not reapplied, corrosion will get worse and eventually destroy the zinc alloy. How long does this take? I can't answer than one, but several years. Lots of factors contribute. The use of alcohol (gas tank treatment, or ethanol) seems to accelerate the process.

Knowing this, why don't all carburetor rebuilders use the dip and reapply the protective coating??? MONEY! The dip used to apply the protective coating is a mixture of Hydrochloric, sulfuric, and chromic acids. Chromic acid (the "active" ingredient) is a known carcinogen and is regulated. To purchase chromic acid, one must have a permit (which requires an approved disposal facility). It is much too costly for an individual (or even small companies such as mine). We send all of our chemical work out to metal laundry companies. Due to the added cost of the chromate and electroplating, most commercial rebuilders don't use it; as most customers are unwilling (either knowingly or unknowingly) to pay for it. Unfortunately, in todays economy, cost (how low can we sell it), not value or performance, drives many marketing decisions.

Jon.

Just a quick follow up......

I have removed all the whitish deposit using a soft brass wheel in a Dremel tool...time consuming but did a nice job..... now I realize from Jon's chemistry lesson that I probably removed some of the chromate coating and whne I sneeze my carb will turn to white dust!!!!!

On the accelerator pump..... it comes apart by removeing the crimped round almost like a washer that hold the learther cup in place....after reverse engineering...meaning I destroyed two to find out...... with a very small flat screw driver you can wedge the blade between the leather and the round washer... hte whole thing comes apart by removing the washer...leather cup and spring over the flat end of the pump shaft.

re-installing is realatively easy if you use a deep small socket thetfits over the shaft...tap tap in place....

Now some caution.... the pumps I disassembled were with a neoprene cup... the one I wanted to instal was leather with a coil spring ring behind it..... and I could not do it.

The profile of the shaft for the leather is rounded and deep to accommodate the spring and leather thickness... the neoprene pump profile is flat and too shallow...... so I am still stuck.

But not stuck for long...... I ordered a new kit from Carbking.... which he promises has the proper flat shaft pump.... now I wait for the postman.....

Out of 5 Rochester carb not one I took apart had a round accelerator shaft...but the kit I purchased had one...go figure....

Now you know why I do not buy lotery tickets.

Thanks for all the good advice from forum members and the personal touch from Carbking.

Bob C.