The Stovebolt Site Forums The Shop Area Engine Shop Testing Rochester B accelerator pump

I think this is supposed to be super easy, but I don't have a frame of reference so be patient. To see if the accelerator pump is working, I'm pretty sure I just need to make sure there is fuel in the float bowl and to look down the throat of the carb (engine not running) and see if I see a squirt of fuel when I operate the accelerator linkage. Is this correct?

I have a reman Rochester B that I just installed. It runs beautifully at idle, but as soon as I press the accelerator it wants to die. I can accelerate slowly and the motor will rev, but if I stomp on it, it dies.

If this is an indication of something being amiss with the accelerator pump, what is the easiest way to troubleshoot it? Like I said, the carb is a remanufactured unit that I got off ebay. It looks amazing and everything is tight.

it sounds like an external adjustment issue, I.E. fuel/air mixture screw, possibly even a slight timing issue, so don't go tearing into the carb just yet.

You are correct about looking for a squirt of gas when operating the throttle valve.
Heed Materman's advice about not tearing the carb apart. It is advisable to save that task for last, as the carb is harder to deal with, and is often not the culprit. Start with checking the easier stuff first, like incorrect timing, stuck intake heat box valve, and vacuum leaks. These will cause that dead spot.
Carl

Theres a very small clip that holds the accelerator pump linkage arm that extends out of the housing and secures it to the throttle linkage. I had that clip come off which caused the pump linkage to disengage the throttle linkage, caused the exact same problem as you describe. This is on the outside and is very easy to see and check. Likes been said don't tear into the carb until you've done all the easy checks.

Dave

Dave, do you have a picture of that attachment. I have to same symptoms that I need to address soon.

The pump should shoot gas just as soon as you crack the throttle. The harder you hit it, the more it should shoot. Give the throttle a couple really quick twists while watching down the carb ( ENGINE OFF ). Did it spray anything, some, or a lot?
Sometimes you can get them working this way, most times you need to go inside and check the check ball and pump itself.

You may need to tweak the linkage a little to get rid of any slop, the pump must move as soon as the throttle does, no lag or taking up wear.

Get back with us and let us know what you find.

I checked the external linkage for the accelerator pump and it's all connected and moves freely when the accelerator pedal is pushed. Here's what I've done so far. My original problem was no power at wide open throttle (I think a bad condenser was causing that).

- New plugs
- New wires
- New points
- New condenser
- New cap / rotor
- New / remanufactured Rochester B

The motor idles steadily at 600 RPM. Dwell is steady at 30º. Vacuum is steady at 19" at idle. Timing is set to point at the circle on the flywheel and it is steady. Idle mixture screw set at peak RPM / Vacuum. Vacuum advance is operational and I can watch it move when revving the engine.

It seems like everything is sorted, but that accelerator pump not producing a squirt of fuel when I move the accelerator linkage is worrisome.

Joe, there is no fuel visible, not even a dribble. I'm pretty sure the accelerator pump is not working correctly. The linkage is all tight and the accelerator pump linkage moves with the accelerator linkage without slop.

I had similar issues on my 235. I went thru everything with a fine tooth comb, and all was in order, yet it still stumbled(sometimes dying) on throttle application. it was squirting a good stream of gas when the throttle was applied while lookin down the throat of carb with engine off. all this with no air filter. once I put a new paper element filter on the engine, this problem pretty much went away. it stumbles a little when not fully warmed up, but once up to running temp it runs great.

This is a manual for a 1951 Model B, yours will be similar, http://www.tocmp.com/manuals/Carbs/Rochester/B/1951-B/MCarbRoch1951-B_0007.htm

I copied the page about the pump system. I suspect your check ball (#5) is stuck, not letting fuel into the pump well. When carbs set for a while, things tend to stick, even rebuilt ones. Even a well worn leather diaphragm will squirt a little fuel.

Joe

Unfortunately a remanufactured Roch B doesn't guarantee that it's a good serviceable carb. I purchased one in hopes it would work on my newly rebuilt 235 as the carb that came with the engine had several issue also. The reman carb had worn throttle shaft bosses and caused a hard to find vacuum leak. Sent it back and he sent it back to me no trouble found.

You should easily see the accelerator pump squirt fuel down the throat of the carb when it's working properly. Since it idles good the assumption is it's getting fuel.

One thing I found out in working on these B's is the fuel bowl has to be nearly full in order for the pump to work on some models. The pump well gets it's fuel via overflowing into the well. Some others use a fill passage and check ball to fill the pump chamber. There's a possibility the float may not be adjusted properly as well as what Joe mentioned above.

My caution about opening up the Roch B was to try not to disturb a non-leaking carb. But it seems you've isolated the trouble to the carb.
Good luck
Dave

Posting the solution here. The float on the carburetor had never been set, the tang that calibrates the float drop was nowhere close to touching anything. This was flooding the accelerator pump well and generally causing issues. Also, the gasket that was used was blocking one of the internal ports. I changed the gasket, adjusted the float, reset the idle and the timing and it runs great now, minus some new, nasty noises from the transmission.