Carter BB Accelerator pump question

[Jims68]

1970 D-200 318 2 barrel Carter BB (or a BBD?) 3 speed manual transmission. Stumbles when I shift and then stomp on the gas, not quite racing, but "moving out". When stopped and the engine OFF, I can SEE the Gas SQUIRT both barrels into the carb when looking at it from above. Can the accelerator pump still be bad? When I "ease" into the gas pedal it is fine with no stumbling. When cruising 50mph?, if I stomp down on it, it'll give a minor stumble. Ease on the gas... no problem. Other than that, it RUNS and Starts great! The only other thing I thought about was a possible vacuum leak around the throttle shaft? But it doesn't wiggle around.

It's just weird that I SEE the gas squirt and thought "how can the accelerator pump be bad if it Squirts?

[martincom]

Is this a new problem on a vehicle that previously performed OK? Or is this a new build/installation?

[Jims68]

Well... to be honest, my truck has been mostly sitting and I really can't recall "if" it did this last year. I thought that "maybe" the accelerator pump may have dried out, shrunk or cracked? They are made of leather. Late last year when it started gas would overflow out the top due to the needle valve would "stick" now and again. I let it sit over the winter. Early this year I took the top off and the bowl was empty/dry. I then cleaned out the bowl and there was some dirt/stuff in there which I got out. Put it together and drove it, but I do NOT remember how it ran. Also, It does not overflow anymore. I put a new fuel pump on and a new fuel filter. Last week or so I finally bought a new battery so I took it for a 30 min. ride and that's when I really noticed it stumbling when I give it the gas after shifting. Today, I looked up about the accel pump and someone said don't let them dry out. I don't know, that's why I asked here if it could be "bad" even though it squirts gas. Maybe I'm seeing gas, but not a strong enough "squirt"?

I also did a search here at Sweptline forums and read this:

...if you ease down on the throttle or does it do it all the time. USUALLY, if it revs okay when the throttle is eased down it's the accel pump. Otherwise it's probably a vacuum leak.

Found HERE: viewtopic.php?p=180025#p180025

[martincom]

It's been awhile since I've had a Ball & Ball disassembled. If I remember correctly, the pump plunger bore, in the casting, is tapered. So the plunger fits more snugly in the bore as it travels. So, this could explain why you see fuel squirt when looking down the airhorn, but still have a hesitation. The accelerator pump is not delivering the "squirt" immediately, as fuel is leaking past it until it travels further into the plunger bore.

If it was just coming off idle that you had the hesitation, I'd be questioning timing. However, as you are also experiencing the hesitation when accelerating at highway speeds, that would dismiss that. With today's fuel, most "classic" engines have to be ran quite a bit advanced from what their published specification was. Of course, with that, you have to guard against to much advance when at higher engine RPMs---which is more than I'm going to get into since that doesn't appear to be your problem. What is your initial timing value?

As your carb dried out, you may want to put a kit in it. They use to sell the plungers separately, but I don't know if that is the case any more. On the other hand, for what you can purchase a new China clone for, it may be more cost effective to go that route, if you can swap jets and metering rods from the existing carb into the clone.

A vacuum leak around the throttle shaft will really impact idle. It'll be rough and you'll have the idle mixture screws opened well beyond the normal amount of turns. If you have power brakes and the booster was leaking, pinching off the hose to it will change the idle speed/smoothness. You can check the PCV valve by pinching off the hose to it. The idle speed will drop around 50 - 100 RPM when the hose is pinched off on a properly functioning PCV valve. You can spray brake cleaner or some other aerosol that is mildly combustible around the carb base and intake passages to check for leaks, while running. You'll hear the idle change if there is a leak when it draws the aerosol in.

[nutz]

make sure your intake cross over isn't clogged
it should be HOT under the carb ,if not the fuel will puddle under the carb instead of vaporizing
then take a second before it has enough fuel to accelerate

[Jims68]

Thanks guys, I'll check the base of the carb with some carb cleaner and see if that does anything. I'd rather rebuild my carb with a new kit rather than a China carb. My top gasket is not leaking gas OUT, but it is wet... so I would most likely need to replace that top gasket anyway. I didn't feel it was a timing issue as the truck ran pretty good other than that persistent cough... do you think it has Covid?

Cross over on the 318? I don't know about that... but the choke opens normally so it must be getting HOT.

[Wildergarten]

A vacuum leak around the throttle shaft will really impact idle. It'll be rough and you'll have the idle mixture screws opened well beyond the normal amount of turns. If you have power brakes and the booster was leaking, pinching off the hose to it will change the idle speed/smoothness. You can check the PCV valve by pinching off the hose to it. The idle speed will drop around 50 - 100 RPM when the hose is pinched off on a properly functioning PCV valve. You can spray brake cleaner or some other aerosol that is mildly combustible around the carb base and intake passages to check for leaks, while running. You'll hear the idle change if there is a leak when it draws the aerosol in.

Nicely condensed diagnostic routine.

[Jims68]

OOPs, I forgot to say that I do NOT have power brakes with the vacuum assist. I haven't "fooled" with it today. Tomorrow it's supposed to rain... But first I think I'll take off the top of the carb and manually push the accel pump down and just see what's going on. I didn't know that the bore for the plunger is tapered!

Thanks!!!

[Wildergarten]

I didn't know that the bore for the plunger is tapered!

The taper is likely due to die casting. One would have a heck of a time getting the part out of the mold without it, the shrinkage of aluminum alloy as it cools being what it is.

[Jims68]

I didn't know that the bore for the plunger is tapered!

The taper is likely due to die casting. One would have a heck of a time getting the part out of the mold without it, the shrinkage of aluminum alloy as it cools being what it is.

Hmmm.... that makes sense!!

[Hobcobble]

I didn't feel it was a timing issue as the truck ran pretty good other than that persistent cough... do you think it has Covid?

It might have the Fratzog Variant?

John

[Jims68]

I didn't feel it was a timing issue as the truck ran pretty good other than that persistent cough... do you think it has Covid?

It might have the Fratzog Variant?

John

You may be right John! I think it needs a double BOOSTER shot (of gas)!

[nutz]

yes heat riser in one exhaust manifold is used to heat the intake manifold rite after the choke comes off
had a 69 dart 273 had a horrible hesitation ,tried timing ,carb ect. never figured it out ,sold the car to a friend and had to reseal the intake
found clogged crossover ,cleaned it out and never ran so good ,the clue for me was it didn't seem to hesitate when cold
if you look down the carb and have a steady stream of gas when you open the throttle accelerator pump should be fine
but if it doesn't vaporize when it hits the intake it will puddle up and hesitate
seems like 4bbl cars seems to spray more of a mist so aren't effected as much

[Jims68]

yes heat riser in one exhaust manifold is used to heat the intake manifold rite after the choke comes off
had a 69 dart 273 had a horrible hesitation ,tried timing ,carb ect. never figured it out ,sold the car to a friend and had to reseal the intake
found clogged crossover ,cleaned it out and never ran so good ,the clue for me was it didn't seem to hesitate when cold
if you look down the carb and have a steady stream of gas when you open the throttle accelerator pump should be fine
but if it doesn't vaporize when it hits the intake it will puddle up and hesitate
seems like 4bbl cars seems to spray more of a mist so aren't effected as much

So if all else fails, I would need to remove the intake and clean it out. No way of doing that "on the truck", right? I've never had that issue before, that's why I ask.

[martincom]

It is simple to determine if the exhaust crossover is plugged. With the engine at full operating temperature, you won't be able to hold your finger tip on the crossover. If you can, it is plugged.

Yes, it is a remove intake repair.

From your symptoms, I doubt this is your issue.

[Jims68]

It is simple to determine if the exhaust crossover is plugged. With the engine at full operating temperature, you won't be able to hold your finger tip on the crossover. If you can, it is plugged.

Yes, it is a remove intake repair.

From your symptoms, I doubt this is your issue.

I'll put my finger on the intake... but I'm holding YOU responsible for burns! HAHA! After some searching I've read where some guys block them off.

OK, so yesterday I took the carb all apart. I felt the plunger was going down kind of "stiff" and dragging like. I put a couple drops of oil on the leather and it goes up and down smooth. Then I took the carb all apart and BLEW out everything as if I was rebuilding it. I didn't find any obstructions in the passages that lead to the accel. squirt ports. Air blew through nicely. Put it together and it didn't change a thing. When the engine is running I look into the carb and gas it. I see both streams of gas spraying into a 'mist'. So, I believe the accel. pump is working as it should. From an idle it doesn't seem to "puff/cough", but only when I change gears and then give it gas. Also, if I'm cruising and "punch" it, it'll give a small cough. I put a tape on the harmonic bal. and marked out every 5* to 50*. I have it at 25* Before and that is where it runs smooth at idle (the throttle return spring doesn't even jiggle), starts good and runs cooler here than if I advance it. This was at the highest idle speed. After I reset the idle, to a normal speed, I moved the dist. again, but it didn't speed up the engine at all. I exchanged the coil with the one from my Roadrunner and I KNOW that one is good. So, that's where I'm at. I also made sure that my plug wires were in the correct firing order, pulled all the plugs and inspected them for cracks or fouling. They looked GREAT not black or white... nice coloring, but I cleaned them anyway and checked the gap at .035. At this point the only thing I am not really sure is the mixture screws and they are backed out about 2 turns each (ABOUT, I'd have to double check and that's why I'm saying this). I don't have a vacuum gauge and I am waiting for a friend to come over with one so I can set them where they should be. However, in all the years I've messed with cars I've never really used one, I would just move them in till it starts to quit and then back it out till it is smoother.

Which makes me think.... would a "new" accel. pump be better?? Is my old one really the simple issue after all this?

[PwrWgnDrvr]

Looking down the carb while running can be really bad if it backfires. Burned face, eyes, etc. Lucky if it only takes eyebrows and hair. Especially dangerous when you're pumping the throttle to diagnose problems. If you must, wear a full face shield.
Drops of oil on the leather will be dissolved instantly in the gas.

[Jims68]

Looking down the carb while running can be really bad if it backfires. Burned face, eyes, etc. Lucky if it only takes eyebrows and hair. Especially dangerous when you're pumping the throttle to diagnose problems. If you must, wear a full face shield.
Drops of oil on the leather will be dissolved instantly in the gas.

OOOhhh.. yeah, good point on looking down the carb if it backfires!

The drops of oil at least helped it go in and that's when I was moving it up and down. Before I had gas in the carb.

[nutz]

don't do it when running
but look down the carb and should have a steady stream of gas as you open the throttle
wonder if your float level is to low and bowl is running empty when your accelerating or to high and flooding
did you check float level and boyancy (the floats can leak and sink)
on 4bbl cars a lot of people will block off the cross over
cooler fuel is more dense so has more power
i know holly carbs spray more of a mist
the other thing is hot soak ...but never seen a 2bbl carter have that problem

[martincom]

I believe you have a timing issue. Your truck likely had a factory timing spec somewhere around 5* BTDC. The mechanical advance of the distributor is likely somewhere around 20*. The vacuum advance around 15*

So if you have your initial set for 25, add another 20 when the mechanical is fully advanced and 15 for the vacuum. That brings you to 60*. Typically, small block Mopars, in a stock configuration like 32* plus or minus a few for a maximum timing value. However, that will very depending on the particulars of your engine. The last thing you want is to be too far advanced and be creating detonation.

I'd suggest you measure your total mechanical advance and record it. Determine it by increasing engine RPM until it no longer advances. Likewise, determine the characteristics of your vacuum advance utilizing a handheld vacuum pump. With the distributor cap removed, apply vacuum with the handheld pump until you just see points/pickup coil began to move. Record it. Next determine at what vacuum level it quits moving and record it. With the engine running, monitor the timing and apply vacuum to the distributor, via the hand pump, and record how much maximum advance the vacuum diaphragm realizes.

It is a pretty lengthy procedure to type out as to how to modify your timing curve. It is late and I'm too tired to do it now. In the mean time, try disconnecting the vacuum advance and see if that improves the hesitation. Next, try retarding your initial timing to 10* BTDC and see if that improves the hesitation.

Where do you have the vacuum advance connected? Ported or manifold vacuum? For your truck engine, you'd typically want to use ported vacuum. Ported vacuum is pretty much identical to manifold vacuum, except at idle. If you examine the drillings of the vacuum port and where they are at in the throttle body, in relationship to the throttle plates, you'll note the manifold vacuum port is below the throttle plates and the ported vacuum port is just above. So, at idle, you'll have no or nearly no vacuum at the ported vacuum port. As soon as you apply throttle, the ported vacuum port is exposed to manifold vacuum and the two become the same level of vacuum.

If you adjusted your timing for best running (maximum manifold vacuum) with the distributor vacuum advance disconnected or connected to ported vacuum, that was great for idle. However, with the vacuum advance connected to ported vacuum, as soon as you come off idle, full manifold vacuum will be applied to the distributor vacuum advance, significantly advancing your timing beyond your best idle adjustment of 25*. If we assume the vacuum advance brings in 15*, your timing off-idle is now at 40*. This is way too much and will cause a hesitation and detonation damage.

I would suggest you adjust your initial timing for best idle with the distributor vacuum advance either temporarily connected to manifold vacuum or a hand vacuum pump with enough vacuum applied to achieve full advance. Next, retard that adjustment a degree or two. This is to give you a little headroom from detonation that can occur with temperature, fuel quality, and engine load. Re-connect the distributor vacuum advance to the ported vacuum port when done with the adjustment. Measure and record your timing for later reference. You may have to re-adjust initial timing if you change the amount of maximum advance the distributor vacuum advance diaphragm can apply, assuming it is adjustable. A vacuum advance diaphragm with a hex shaped nose has an adjustable mechanical stop to limit the maximum amount of advance. It is adjustable by reaching through the vacuum port opening with an Allen wrench (aka: socket head) into the adjustment screw. You may be changing this setting later.

The factory service manual, in the electrical section specifications, will have published values for mechanical and vacuum advance of listed distributors. There will be an ID tag with a part number affixed to the distributor, if it is OEM. Match that part number up with the listing in the specifications. I'd still measure the actual advance of each and compare it to the published specifications.

Let me know where you are at and I'll provide more info a bit later.