Motorcraft 2150 big/accelerator pump

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mopar440

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1989 jeep grand wagoneer w an AMC 360

I installed a rebuilt 2150 2 barrel carb. I've become fairly familiar with it, and fixed a few mistakes on the rebuid

However, I have a bad bog on acceleration past 1/4 throttle. You slowly accelerate, and it doesn't bog

Checking the accelerator pump, it seems to run out of fuel around half throttle. Sure ses like it should have a good squirt all the way through the throttle stroke

I've adjust the throw on the throttle lever, and tried every hole

I'm thinking it could be easily the wrong diaphragm or something but LOOKS right. Check ball and weight are installed

Any other ideas?
 
That test was engine off. When running, revs fine in neutral, and accelerator pump squirts the whole travel. That may be due to the engine vacuum tho
 
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Once past about 1/2 throttle, no real need for the accel pump. Past that point, it's the "power valve" that supplies enrichment.

If you have "a bog" when desiring something more than normal throttle input, after the initial accel pump shot, it's the power valve that keeps things running until you back out of the throttle. From your description, I suspect the power valve is not as operational as it should be. Possibly blocked by an incorrect gasket?

Keep us posted,
CBODY67
 
CBODY67 said:
Once past about 1/2 throttle, no real need for the accel pump. Past that point, it's the "power valve" that supplies enrichment.

If you have "a bog" when desiring something more than normal throttle input, after the initial accel pump shot, it's the power valve that keeps things running until you back out of the throttle. From your description, I suspect the power valve is not as operational as it should be. Possibly blocked by an incorrect gasket?

Keep us posted,
CBODY67
Click to expand...
Interesting...I thought the power valve was more for enrichment " farther down the line" not, just straight off the throttle

I know I had it out, and everything looked ok. I know they had problems with that gasket leaking on these, but that usually floods it out, hard start etc
 
The power valve opens ANY time the manifold vacuum drops below a particular level. The standard Holley power valve used to open at 5.5"Hg, generally, although there were a whole lot of variations in them, with individual part numbers for them.

A "power valve" is for "fixed-jet" carburetors, usually. The accel pump gets it "off the line", as the power valve takes over at higher rpms. BUT, it CAN open at idle if the manifold vacuum drops below it's opening point. to a point, the accel pump mightr fill an ever-smaller "gap" in mixture at off-idle accelerations, but past that point, it's not needed and any additional fuel provides no additional power is realized.

Such "at idle" openiongs are usually the resuslt of "too much cam", not enough idle speed, and "a too tight for the application" torque converter. None of which should be operative in your situation.

On "metering rod" carburetors, as the metering rods move upward, to allow more fuel into the mix, no need for a vacuum-operated power valve. In some cases, the "power piston" (to which the metering rods are attached) can stick and cause lean mixtures as a result of the metering rods not moving upward in their travel.

From what I discovered, your application is supposed to have an "Altitude Comnpensation" item. There probably is some sort of rubber diaphram associated with that, possibly working against spring pressure, modulated by mainfold vacuum?

We have a '69 Chevy pickup. Normal 350 4bbl with 3.73 PosiTrac. With that rear axle ratio, it doesn't take much throttle to move it along. Dad always drove slow and easy, so the power piston started to stick. After the accel pump shot was used, all acceleration ended, except for very casual acceleration, even at WOT. So the gap between idle and when the secondaries started to open was very obvious to me. But very gentle acceleration worked just fine for him.

Years later, on a "1/2 QJet" Rochester 2bbl, a friend had one that had had many carb rebuilds. Same complaint. No acceleration/power. After a few checks, we determined that the power valve was not moving as it should. When the carb's top was removed, there was no spring under the power piston, which meant the metering rods were in "Economy" position, all the time. A new spring under the power piston resulted in "tire noise". The customer was very pleased! After so many carb rebuilds, he wondered why nobody else had noticed that!

Enjoy!
CBODY67
 
I'm thinking of hooking up a vac gauge inside and seeing when it bogs. Any other suggestions?
 
It does have the high altitude set up, but not the variable venturi metering rods
 
mopar440 said:
I'm thinking of hooking up a vac gauge inside and seeing when it bogs. Any other suggestions?
Click to expand...

Might check the vacuum advance can for a vacuum leak, too, if you've not already done that.

Take care,
CBODY67
 
CBODY67 said:
Might check the vacuum advance can for a vacuum leak, too, if you've not already done that.

Take care,
CBODY67
Click to expand...
Yes, already did that. However, these are odd, as they go through temperature switches for emissions

Anyone aware of a cheaper wide band o2 set up that I can stick in the tailpipe? I've been holding off for years, but one would come in handy right now
 
Thermal Vacuum Switches were common back then, but I don't know why they'd be in the dist vac advance plumbing. There should be a vacuum line map on a decal under the hood.

Typical TVS were used to keep EGR closed until the engine wa wamred-up. To operate other things before the engine warmed up.

Thanks,
CBODY67
 
CBODY67 said:
Thermal Vacuum Switches were common back then, but I don't know why they'd be in the dist vac advance plumbing. There should be a vacuum line map on a decal under the hood.

Typical TVS were used to keep EGR closed until the engine wa wamred-up. To operate other things before the engine warmed up.

Thanks,
CBODY67
Click to expand...
Yes, the decal is gone, but I followed diagrams. The vacuum advance and egr go through 2 separate thermal vacuum switches, it's crazy...

Ordered a wideband o2 set up for testing, it will be here Monday
 
Wondering if the TVS changed the dist vac advance from ported to manifold vacuum sources as the engine temp increased? Or vic versa? As mentioned, the EGR delay until the engine temp was at a certain level is normal.

Please keep us posted,
CBODY67
 
No change, however have a steady 16 inches vacuum at idle in neutral that seems lower..

And the port to the vacuum advance cold had about 1 inch, and raised with throttle to 6, that seems odd to me
 
mopar440 said:
No change, however have a steady 16 inches vacuum at idle in neutral that seems lower..

And the port to the vacuum advance cold had about 1 inch, and raised with throttle to 6, that seems odd to me
Click to expand...
Swapped vacuum advance hose to ported vac, wala, seemed to work!

However, in hooking stuff back up, took plug off power valve cover and saw...gas...blown valve, awesome...

Removed carb and look here....a plugged solid hole, I assume it's the power enrichment hole...can barely scrape it out, what ever it is...

Got a warranty carb coming

IMG_20201004_162615362.jpg
 
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