MC 2150 Accelerator pump spring question

[tirewater]

I'm getting a hesitation when leaving from a stand still. I've gone through and fixed vacuum leaks (leaky power brake booster!).

I adjusted the idle circuit using a vacuum gauge. Timing is at 8 degrees BTDC. Distributor vacuum advance is plugged into ported vacuum.

I'm suspecting the accelerator pump, and perhaps incorrect assembly by the reman. (!!).

The throttle shaft has the throttle lever, kickdown lever, accelerator pump lever. There is a C-Clip that holds the kickdown lever next to the throttle lever.

The spring on the shaft presses against the accelerator pump lever. This preloads the accelerator pump and the pump piston itself is pushed about 1/3 of a way into its travel. Is this correct?

(I'll go take some photos)

Essentially the return spring on the throttle shaft is using the accelerator pump lever as a stop for the throttle. I would've thought that this spring would use something stationary on the shaft rather than the accelerator pump lever.

The photos have me pressing the accelerator pump lever against the counter spring so it relieves pressure on the accelerator pump piston.

First picture is where the lever 'rests' normally. Second picture has me pushing the lever back against the preload spring.

 

[jckkys]

Everything appears correct. The spring wound around the throttle shaft is intended to over power the spring under the accelerator pump diaphragm, and allow time for the fuel to get through the nozzles after the throttle is slammed open. The accelerator pump lever you're pointing at, stops when the throttle shaft is about 3/4 of the way to full open. It's done it's job by then.

 

[broncodriver99]

What hole is the accelerator pump linkage in on that lever?

 

[tirewater]

What hole is the accelerator pump linkage in on that lever?

Second from the top, third from the bottom. This appears to be the correct setting in this application.

Accelerator pumps are cheap, I can try replacing it "just because". There are various stem lengths, perhaps I have one that's too long.

Or I'm just grasping at straws. 8 degree initial timing is a bit low, but I'd expect it to run somewhat decently.

 

[broncodriver99]

8 degree initial timing is a bit low, but I'd expect it to run somewhat decently.

Stock was 6 degrees so it should be doing ok. I bumped mine up to 10 and some run even higher. 10 degrees did smooth it out considerably.

 

[tirewater]

I believe I found the problem. The accelerator pump lever & spring on the throttle shaft have some side to side play, which causes it to decouple from the throttle lever. This allows the torsion return spring on the shaft to close the accelerator pump.

Here is the at rest state with the pump partially depressed, and with me manually pulling the lever forward. (eh, the other way around, the pictures are in reverse order)

 

[tirewater]

Here are two images showing the space on the shaft. I need to find something to fill the space and keep the lever & spring against the kickdown lever.

 

[broncodriver99]

Yep that's a problem. Looks like you may have the wrong diaphragm. There are several.

http://www.carburetor-parts.com/Accelerator-Pump-Diaphragms_c_953.html

 

[jckkys]

Most the 2100-2150 rebuilding kits have an early style pump diaphragm and yours looks like a long stem '77. Included in these kits is a steel cylinder that's 0.25" diameter and 0.68" long allow the no stem diaphragm to work on your 2150. There is no piston in a 2100,2150, or 4100 Ford carburetor just a diaphragm like Holley 2300,4150,4160, or 4180s. The accelerator pump arm on the throttle shaft stops when it hits the front of the casting protrusion that also holds the the idle speed adjustment screw. The throttle shaft turns further against the spring till it hits a round protrusion in front of the throttle shaft. The pump diaphragm isn't bottomed out. In fact the diaphragm is compressing through the whole range of throttle shaft rotation, or about 85 degrees. The first 30 to 40 degrees is all that the accelerator pump arm moves. Any movement of the throttle from fully closed must have corresponding depression of the diaphragm to avoid a stumble. Another important thing to look for, is the check ball and weight under the booster venturi cluster. They keep fuel in the accelerator pump circuit from draining back into the float bowl. If this happens, the first movement of the accelerator just refills the circuit instead of squirting at the booster to avoid a stumble. The space between the spring and the kick down lever was filled on earlier models by an added section of the accelerator arm (same piece of metal) that you see over the spring that went on to include a second washer between the spring and the accelerator arm. It looks like Ford saved some money deleting it. No loss tho, as it has nothing to do with your off idle stumble and has no effect on the operation. Any play in the accelerator pump linkage or missing check ball and weight will cause a stumble.

 

[tirewater]

Thanks guys,

I corrected the issue with the throttle shaft, yet that didn't solve the issue.

I removed the accelerator pump housing & diaphragm. The diaphragm doesn't have holes in it, but is fairly stretched out.

I touched the accelerator pump check valve and it fell apart.

I just purchased a kit + check valve from Mike's carbs. I'm not going to do a full rebuild, but I have to pull the top off to get the other piece of the valve out.

I'll check/set float bowl height while I'm in there.

 

[jckkys]

The red rubber umbrella check valve under the accelerator pump diaphragm usually breaks if you try to remove it, but that doesn't mean it wasn't working. The check ball and weight are under the booster venturi cluster, and often not assembled correctly. If fuel isn't squirted out of the accelerator system nozzles with ANY movement of the throttle you have a problem that will cause a stumble or more correctly a hesitation. The cause has to be found and corrected. The space on the throttle shaft is irrelevant.

 

[tirewater]

I'll look at the check ball and weight when I pull the carb. I've downloaded multiple 2150 manuals, including the one on Mike's carb site. Hopefully I have enough reference material.

 

[tirewater]

Some carb shots.

 

[tirewater]

More shots.

 

[tirewater]

Size 50 main jets. If I can source some locally, I'll be dropping down to 47-48. That could potentially be the issue with bogging off idle.

 

[broncodriver99]

I thought the 1.21 venturi carbs were for 351 W/M and larger engines. I believe stock would be a 1.08 venturi carb. That may be part of it as well. Maybe thats why you have the 50 jets.

 

[jckkys]

The fact that National Carburetor sent you an incorrect carburetor isn't surprising. It would be surprising if they sent you the right one. The 1.21" venturi was likely off a 351W where it would be correct. I hope you didn't make the mistake of letting them have your OE 2150 for an insulting core charge. Being a 1.21" venturi model, the 50 jets are correct. On a 302 or 1.08" veturi version smaller jets like 47-48 are correct. Smaller jets in your 2150 will produce a lean mixture in cruise mode, likely resulting in over heating. Regardless, jet size will have no effect on an off idle stumble or bog. Accelerator pump shot or fuel delivery is likely delayed or of insufficient volume. The next possible cause is an under size idle feed restriction. Ideal initial timing for your engine is just that, not some factory specification. I run my 351 with 20-21 degrees.

 

[tirewater]

While I'd prefer a 1.08 (287cfm) versus the 1.21 (351cfm), I'm going to try and not worry about it too much.

National likely has several configurations spec'd for the 302, and I just happened to get what was available.

This carb came from Autozone. I wanted to use a parts store for convenience of returns. The parts stores sell United, National & Tomco - none of them have overwhelming reviews.

Of course I voided warranty already, but I could likely still return it.

Regardless, National sells one *clean* carburetor.

I'm still leaning toward a faulty/broken accelerator pump check valve. The tip of the valve in the float bowl is missing. An overzealous rebuilder may have ripped the valve when installing it.

Something to look for in the carburetor itself.

The rebuild kit comes today. I picked up a brass float bowl for kicks, as well as three additional accelerator pump check valves in case I rip them.

My first tear down of a automotive carburetor. I've done numerous motorcycle carbs, but never an automotive one.

The fact that National Carburetor sent you an incorrect carburetor isn't surprising. It would be surprising if they sent you the right one. The 1.21" venturi was likely off a 351W where it would be correct. I hope you didn't make the mistake of letting them have your OE 2150 for an insulting core charge. Being a 1.21" venturi model, the 50 jets are correct. On a 302 or 1.08" veturi version smaller jets like 47-48 are correct. Smaller jets in your 2150 will produce a lean mixture in cruise mode, likely resulting in over heating. Regardless, jet size will have no effect on an off idle stumble or bog. Accelerator pump shot or fuel delivery is likely delayed or of insufficient volume. The next possible cause is an under size idle feed restriction. Ideal initial timing for your engine is just that, not some factory specification. I run my 351 with 20-21 degrees.

 

[tirewater]

I hope you didn't make the mistake of letting them have your OE 2150 for an insulting core charge.

You helped me identify my previous carb, which was a Holley 2300. It went into the trash. No core returned. I have no idea where the original Motorcraft carb went.

 

[jckkys]

I keep forgetting that new Bronco owners are often stuck with an accumulation of knucklehead choices by a few or many POs. I've seen the large scale "rebuilders" offer carbs they can't claim are correct, so they use terms like "fits". Hell almost any 2 barrel Ford, Holley, or Carter will "fit" any 2bbl intake. They often send a 2100 and call it a 2150. Getting them to reveal the venturi diameter or the whereabouts of the ID tag is impossible. The booster venturi cluster may be from a different, read smaller, 2150. This would mean the IFR or idle feed restriction is too small for a 1.21 venturi. Meaning the idle transfer slot, that is not adjustable, is delivering a lean mixture just as the throttle is opened. It would also have smaller accelerator pump nozzles. Both of these would explain an off idle stumble. I searched for a rebuild-able, equivalent 2150 that could be rebuilt or used for parts, at a reasonable price, and found this;http://www.ebay.com/itm/Ford-Motorc...ash=item1a13769c0e:g:iUUAAOSwvU5XNLhh&vxp=mtr. The ID tag tells me this is a '77 truck 2150. It's a good investment by itself and has a good chance to provide donor parts to fix your problem.