Accelerator Pump Parts Squirter Nozzle

[blackrag]

I'm trying to use a 3310-2 750 vacuum secondary on a street engine. No matter what, I can't get a pump shot. After watching the videos and adjusting the pump arm, verifying fuel pressure, and float levels, no pump shot. Taking the front bowl and metering block off, I believe I installed the gasket backwards which I think blocked off the passage. Anyway, I pulled the squirter/nozzle off and according to the part schematic, there's supposed to be a ball weight under the nozzle? There was none. Is it necessary? Thanks, Chad

[69cam]

It functions as a check ball assembly to stop any siphon affect. You should be able to manually pump the accelerator pump arm, and watch fuel squirt. If not, you got the gasket in wrong, or the diaphragm in the pump assembly is messed up.

[81 TransAm]

In older carbs, they used a check ball under the pump diaphragm. In newer ones, they used a rubber umbrella to stop the fuel from pushing back up into the fuel bowl, when the accelerator pump is depressed.

[blackrag]

Tonight, I pulled the carb again. Replaced the pump diaphragm, replaced the meter block gasket installing it correctly, double checked pump arm adjustment, installed check needle under nozzle, reviewed float levels, verified fuel pressure @ 6 psi.

No pump shot. Have to pour a few ounces of gas to cold start the car. Once running and warmed up, I can drive the car, as long as I don't need to accelerate hard. If I try to accelerate, it bogs/wants to die. Drove a few miles to a gas station, filled up, and the car started up and drove home. Still no pump shot.

This is the type of accelerator pump a 750/3310-2 has, there is no check ball. What else can I check?

[69cam]

You can start by taking the bowl off. Since it just had gas in the assembly, move the actuator arm. Is fuel squirting out? If not, it's in the bowl/actuator assembly. If it squirts gas, take the metering plate, line it up on the bowl, actuate the arm. Did fuel squirt through the metering block? If not, some blockage in the metering plate. If so, then has to be something in the carb body.

[69cam]

You can start by taking the bowl off. Since it just had gas in the assembly, move the actuator arm. Is fuel squirting out? If not, it's in the bowl/actuator assembly. If it squirts gas, take the metering plate, line it up on the bowl, actuate the arm. Did fuel squirt through the metering block? If not, some blockage in the metering plate. If so, then has to be something in the carb body.

So I spent some time (5 min) downloading picture to show you what to look for:

Above is a Holley fuel bowl from a 4150 style carb. Yours may be a little different but you can see the small hole in the bottom left corner of the bowl, The accelerator pump pushes fuel through this hole when the lever is depressed. Get this working first. Blow through passage, manually put some fuel in the diaphragm area to make sure it has fuel and pump it to see if fuel squirts out this hole. If not, something wrong with accelerator pump assembly passage etc etc.

The above picture is a Holley metering block. In the bottom right corner you will see a hole that lines up with the hole on the bowl for the accelerator pump. Get some wd40 and use the red nozzle to blow some WD40 through metering block. You can see in the picture that passage travel up in a diagonal passage to the center of the metering block and comes out on the other side. Make sure this is flowing.



The above pic here is the main body of the of the carb. Right in the center of the block is hole "D". hard to see the letter but its the only hole in the center of the block. That hole leads directly to the discharge nozzle. Again, blow some wd40 through here and see if it will discharge out of the nozzle.



The above pic is a cutaway of the bowl & metering block, that shows the entire path of fuel from accelerator pump all the way to the nozzle.

You should be able to find your problem and address it from here.

Thanks, Sean

[blackrag]

Thanks Sean, for going through all that trouble.

1. I pulled the bowl off, pumped the actuator arm, and fuel came through the lower hole.
2. Holding the metering block in place, tried to push compressed air through the matching passage, no air came through the nozzles.
3. Pulled metering block off, air easily moved through the passage in the block.
4. Ran compressed air straight at the carb body, and it faintly passed through the nozzles.
5. Pulled shooter nozzle, it was clean.
6. Pulled pump weight out of passage.
7. Now compressed air blows through freely.

Thinking there must be a burr on the weight, I polished it up and put it all back together. Still the same result, no pump shot.

Later today, I plan to pull it apart again, remove the weight, and see if I get a pump shot. If it resolves the particular issue, I wonder if I could run without it.

I'm narrowing it down to 2 possibilities.

1. There is an issue with the bore below the nozzles, that doesn't allow the weight to move freely.
2. My new diaphragm isn't good enough to put out enough pressure, or somehow I have it upside down?

[69cam]

That's good progress. So now we now know it's the check ball assembly. You pull it out and I'm most certain you will get a pump shot. I would make sure the shooter nozzle assembly allows the check ball assembly to come up. Put the check ball assembly in, but no shoot nozzle and LIGHTLY actuate the accelerator pump arm. See if fuel flows.
Maybe the wrong shooter nozzle or wrong check ball assembly. Something goofy like that.

You blew through the shooter assembly right?

If you wanna just pull the check ball assembly, my concern would be it dribbling fuel. Run the motor up to 2500-3500 RPM in park, and after the initial shot, watch the nozzle see if drips fuel while at 2500-3500 RPM.

I'm not 100% sure if that check ball assembly is there to keep fuel from dripping out or to keep the passage loaded with fuel, so that when you touch the accelerator, fuel instantly squirts out, as opposed to have to fill up the passage way and require a couple of pumps, before it actually squirts fuel out of the shooter.

[blackrag]

Found the issue. When I initially rebuilt the carb, it had no check valve (plumb bob) under the pump nozzle. Evidently there was a reason for that. After pulling my hair out tonight, I put a depth gauge in the screw hole to the top of the check valve, and realized the screw holding the nozzle was locking the check valve and not allowing it to pop up under the pressure of the pump stroke. I turned one thread off of the 12-28 screw and ground about .1875 off of the top of the check/plumb bob. Now I have a resemblance of a pump shot.

I was able to check the idle with a vacuum gauge, highest I can get is 11 Hg at about 1.5 turns out. Same at lumpy 800 RPM idle and in drive.

While much less, I still have an off idle stumble, maybe I need to go bigger on the nozzle. Currently a 31. I have 71 primary jets.

Thanks Sean.

[69cam]

Your welcome, glad I could help.

Before I started messing with changing shooter sizes, pull the needle check valve assembly out. See if you still have stumble. Putting the next size shooter would be putting a band-aid on the problem, if the needle check valve assembly is the real culprit.

Also, make sure your timing is set & good.