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I've reached the end of my knowledge and search abilities, and am reaching out for help! The accelerator pump system on my rochester B is not working and I can't figure out why.

Truck will start and idle ok if I give it a shot of starting fluid, but will not start on it's own and had a severe bogging when giving it sudden throttle. I thought a carb rebuild would solve the problem as it just seemed like the ACL pump was bad. I put the new kit in, triple checking that everything was correct, put the carb back on and symptoms still exist.

I've now disassembled the carb 5 or 6 times checking everything and still nothing works. Without the top of the carb on when I press down on the ACL pump it gives a solid shot of fuel from the discharge tube. When I put the top back on I get no fuel squirt down the venturi.

Things I have done.
-checked and rechecked float levels (both)
-checked power piston for free movement and that the check ball is unseated
-checked ACL pump is pumping through dischage
-checked that discharge check ball is sealing and fuel stays in discharge tube when ACL pumps raises.
-checked that all ports and passages were clear of any obstructions. I've blown air through every orifice and they all seem clear. I let the parts soak in cleaner for 48 hours to clean everything up.
-There is no warpage of float bowl and it shows no signs of leakage.

I'm stumped, [censored], and reek like gas. Any ideas are welcome.

I know someone is going to say get rid of the rochester, which is not off the table at this point, I just don't know what other carb to put on a 261. I don't want to run dual carbs at this time.

Looks like you checked most everything.
How are you actuating the pump rod with the cover on? With throttle movement or by hand with just the rod? Verify you have the correct amount of travel or any at all.
Make sure the top gasket is not blocking any passages that should line up with the main casting or push ACL out of position.

I didn't have time to read all your posts, but has the intake manifold ever been removed? If so it's real easy to "missalign" the intake, when re-installing. I've done this a couple of times while working on an old stovebolt. The alignment rings can hang up in the port and cause a major vacuum leak! I can relate to your frustration, I've been known to make the same mistake over and over? Maybe you can get another mechanic to take a look, get a fresh perspective? Good luck!

I know you want to figure it out just like I would, but after all that work, I would put on another Rochester. No use getting frustrated, move on to something else and figure it out later. It will also give you something to compare and study the difference you see. Then you will find the problem. hd4unm has good thoughts. It is also possible that you run out of gas in the bowl after your "test pumps" and there is a problem with fuel delivery to carb. Fuel pump, dirty filter, clog somewhere, unvented tank? you may want to do a test for that. Take off line at carb, turn engine over and see if it fills a cup pretty fast. It will pulse, splatter and probably start a small fire, so be careful. Unhook the main, center distributor wire so no spark. Carbking will know.

With the Carb off the manifold and the float bowl full, I fully open the throttle lever. This should make the ACL pump squirt fuel right?

I am positive that the ACL pump is moving in the well. With the top off and the well full of fuel when I depress the aCL pump arm and fuel comes out of the discharge hole.

I've tried both gaskets that came in the rebuild kit. They don't appear to be blocking off any holes. I do wonder why there is a hole in the gasket HERE It lines up with the discharge port on the top of the bowl portion of the carb, but then the top cover has the hole in the gasket that is just blocked off.

The tank has been cleaned and resealed and the fuel going to the filter appears to be clean.

Manifold has been off, but I had it resurfaced and I am pretty sure it is sealing properly, engine runs ok at idle if I can get it started. How would that affect the ACL pump circuit?

If I buy another carb, it won't be a B

I can completely sympathize with what you are going through. Had the same problems with my Rochester B. In fact, I rebuilt two of them (bought three to get enough parts as they are cheap), but I only rebuilt them four times, not five like you...

Still had the same symptoms you described, though maybe a little less severe.

The last straw for me was on the final rebuild, went for a test drive and the truck died at a (thankfully) rural intersection. Would not restart. But when I looked in the engine bay, the Rochester was pouring fuel out of the accelerator link hole, all over my hot exhaust. Scared me to death. Standing there on the side of the road, fire extinguisher in hand, and waiting for my investment of a years' worth of time to go up in flames, I decided that $125 for a professionally rebuilt carb would be a good investment.

Sent away to a company in CA and swapped out my Rochester for a shiny Carter YF 2100S.

Have not had a lick of Carb trouble since.

I know it's not where you want to go, but it's worth considering.

Best of Luck,

Jim

...and the fuel pump is pumping as it should? Volume wise? and the bowl in staying full? If I understand correctly, the engine was running and starting OK and THEN something happened? That leads one to believe that is was not a blocked hole and all that in the first place. It leads me to question a failure in delivery or something worn out in carb. Not much "wears out" except the Accelerator pump, needle and seat, warpage, corrosion... so that's why I say put on another carb to see and also check delivery. Rochesters are good carbs. I know you know this but: There is float level adjustment and float drop adjustment. Did you do drop also? There are TWO BALLS: Pump discharge and pump check (not all have this one),supposedly the check ball is aluminum and the other is steel and they should not be mixed. If they are missing or old one stuck and new one installed on top, you will get exact result you are getting. You say discharge tube squirts but after top goes on no venturi squirt, so does air pass thru wherever the discharge goes to venturi outlet?
P.S. If Jim would have sent away for a shiny Rochester, he would also have "not had a lick of carb trouble since."
Disclaimer: Not a carb expert, never had a B model, have rebuilt many Q-jets/2-jets, just trying to brainstorm and help until carbking sees this.

try getting a new float, might be the problem

How much fuel should a fuel pump pump if a fuel pump should pump fuel? How to I check volume of fuel?

Truck has never started on it's own since I took ownership and I don't know the history of it before that as the owner had passed.

The check balls are in the correct position and are new. The pump discharge did not seem to seal well so I hammered it down in the hole with a brass punch until it seemed to seal better.

I checked both float level (1 5/16) and float drop (1 3/4)

Fuel Pump & Vacuum Tester - instructions are downloadable.

I think the float level is 1 9/32. Your folat lavel may be low. I think the gas runs in the groove in the side of the cyl. & goes through a check valve in the pump plunger. Its stange that it works with the top off & not after it is assembled. Is the linkage good? sometimes it gets worn & the throtle moves a ways before it moves the punmp. Ive run model B carbs for years & never had much problem from them.

The only addition I could add to your testing would be to fill an empty squeeze bottle (mustard? ketchup?) with gasoline, and squirt this through the passageway to the pump discharge nozzle to make certain this passageway is open.

Original 261 carbs are neither easy to find or inexpensive when you find them. The commercial rebuilders group them with the smaller 235 carburetor, which will reduce power.

(Opinion) If it were my truck, and I wanted to drive it rather than look at it, the Rochester single barrel would leave the engine as soon as I could get it off, and the truck would sit unstarted (yes, I would look at it for awhile) until I could find a real carburetor. A good choice would be a Zenith from a G.M.C. 270. Stromberg also made some excellent replacements, but they are scarce and expensive.

And Bart, I share your opinion of the Q-Jet and the 2G; some of the finest carburetors ever built anywhere in the world at any time or any price. As to the B, a useful upgrade is to hire a 15-year old to stand on the running board and pour gas into the engine out of a leaky boot!

Jon.

If you have a pressure tester it's probably supposed to have 2-4 PSI. If not, see my proceedure above. Let tube shoot into a plastic water bottle or equiv while cranking motor. It should pulse and shoot a good stream. You will know if it's good or not by observation. Keep it contained into the bottle, need extra person to operate motor. I guess Jon amd the internet say the B is no good, so don't waste any more money on it. After you confirm you have good fuel pressure, get one of the carbs he mentions.

What model Zenith would I be looking for?

Not only a fair point, but to the point (and well spoken Sir). And, as the purpose was to help diagnose what he already had, I have to agree.

Shutting it...

Respectfully,

Jim

Call, Click(website) or PM the carbking for what model Zenith. He may have one available.

Wow, I feel kind of dense. After hours of staring at the thing and trying to picture in my mind how the AC pump moves fuel through the carb, I finally figured it out.

Discharge hole was clogged with trash, after cleaning it out, truck starts right up and accelerates pretty smoothly.

I was seriously over complicating the problem.

Thanks for all the input

Fixing something yourself is always a great feeling. Good Job Dog.

Shoedog:

If you have been on this site for any length of time, you know that I am far from an expert. That being said I empathize with your problem. I had a very similar issue on my 58 Suburban. It has a later model rochester monojet carb. I had very similar issues with getting it running and trying to accelerate.

I bought a rebuilt kit and did my first-ever rebuild job on the carb. I blew through two big cans of carb cleaner and was convinced that I had a completely clean carb. When I put the carb back on the engine there was a huge improvement in starting and running. It still sputtered badly during acceleration. I fought with it for a while and finally had to through in the towell. Luckily there is another very generous and helpful Bolter in the area (Joe H) that came over to the house and saved my bacon.

After much exploration and experimentation Joe decided that there must be a piece of crud blocking some internal passage in the carb. He ended up taking it to his work where they have a big industrial solvent tank. He dissassembled it and soaked it for a few days and then put it back together for me. When he brought it back to the house I didn't even recognize it. It looked brand new. Now the truck runs like a scalded cat.

My point is that the carb may not be as clean as you think. Joe got junk out of passages that I didn't even know existed. If you have access to a solvent tank or can hook up with a Bolter in your area that can help, I highly recommend a long soak in the good stuff to clean out your carb.

That is what really worked for me.

Ok, discregard my last post. Should have read all the way to the end first. Doohhh!