440 hesitates on light throttle

[Frank Mopar]

If you have the eddy set in the top hole you need to bend the rod to get more pump shot. Thats in their directions.

 

[71GTXdragpack]

A Start

If its the factory carb for a 71 GTX U Code 440HP

Carter AVS 4968 Auto
Carter AVS 4967 Manual

We would start with the leather accelerator pump LIKE MENTIONED , especially if the carb has been sitting for an extended period of time

You ever rebuild , or open up a Carter AVS ?

Do you know if it has the factory distributor ?

If it does , it came with the vacuum advance with the electric retard feature

That in itself can be a major headache when it comes to the distributor and vacuum advance

PICTURES ???

Would bee nice or

It's a 4 speed with Carter AVS and I have never rebuilt a Carter. Appears to be a factory distributor with points ignition. I'll post some pics later today.

 

[71GTXdragpack]

Hi all,
after spending most of the winter getting the Dana installed and sorted out, now I'm back on the hesitation issue. First drive this summer, the car ran great, after filling up with fresh fuel, it started doing the hesitation at light throttle again.
I've changed the plugs and wires, new fuel filter, readjusted the timing to 16 degrees advance and confirmed that the vacuum advance does work. I've run with the distributor vacuum blocked and on, it hesitates either way. I've tried to spray carb cleaner down the throat and still hasn't improved. At this point, I have to think it's either points, capacitor or accelerator pump.
Any definitive way check so I'm not just replacing parts?

 

[Bee1971]

All the early posts in this thread told you accelerator pump

If it is indeed a factory Carter AVS like you are saying , chances are the original leather accelerator pump material has dried up causing the symptoms you are describing

Only way to confirm , you would need to pull the top off the carburetor

Know anybody that could remove your carb , or at least pull the the top off (The accelerator pump will come off with the top of carburetor) and have it taken apart and looked over

That’s where I would start first before digging into the distributor - If it is indeed a factory correct 1971 HP 440 Points Distributor , the Vacuum Advance / Electrical Retard is another headache

 

[Bee1971]

It's a 4 speed with Carter AVS and I have never rebuilt a Carter. Appears to be a factory distributor with points ignition. I'll post some pics later today.

Pictures , today was a year ago , and your still going to get the same answers today as you did a year ago

Peace

 

[71GTXdragpack]

my bad, please see pics with air cleaner removed.
Without reading the P/N's...the carb appears to be a Carter and distributor is a factory single point.

Any help is appreciated.

 

[Orig69]

Try advancing the ignition timing to 15 degrees to see if the hesitation goes away. Also try removing the vacuum advance hose and plug the port.

The gasket for the air cleaner is missing.

 

[oldbee]

Take the top of carb off. If the acc.pump is leather try flaring it out from the spring that is inside the leather. Put back together & drive it, if it helps the hesitation buy a new acc. pump. Bet ya that’s the problem; Old leather or worn new style.

 

[Geoff 2]

Buy a carb overhaul kit with new acc pump!!! The car has earned it......

 

[Jonas Nordstrom]

With the acc pump rod in the hole closest to the carb body you get the shortest travel and lots of fuel quickly.

Play around and test the hole furthest from the carb body to get a slower duration fuel squirt.
(For ex this is what my engine likes.)
Dont forget to bend the rod for the correct ratio.

Also add the leather plunger if you havent allready.
With fuel in the carb, look down at the squirter nozzle.
If healthy the fuel should squirt out as soon as you just touch the throttle arm.
Good luck.

 

[71GTXdragpack]

Try advancing the ignition timing to 15 degrees to see if the hesitation goes away. Also try removing the vacuum advance hose and plug the port.

The gasket for the air cleaner is missing.

the timing is at 15-16 degrees currently. I did try removing the vacuum advance and plugging the carb but it made no difference. I looked down the carb the best I could as the car is really wide and it seems to squirt fuel properly. Guess the next thing to do is the acc pump.

 

[Bee1971]

All stuff mentioned

Carb looks great , nice and clean obviously gone thru or rebuilt prior at some point

Can you see carb # stamped number bottom base left corner by mounting bolt

Is your choke fully functional

Can’t tell in pictures but is your choke pull off working along with your choke spring heat stove



Want to make sure your choke plate is opening all the way when engine hot and partially open when cold

Also your distributor is not factory correct for that year - Better off with that style vacuum advance anyways

Next thing after going thru carb look over your points and condenser , dwell

 

[AR67GTX]

That carb looks pretty fresh, maybe even professionally restored at some time. I would pull the carb off and get a rebuild kit and pull some Carter rebuild info off the internet. Before going any further put a little gas in the driver side vent tipubes to make sure there is fuel in the bowl. Then with the carb sitting over a pan, slightly rotate the throttle arm and se3 if fuel is instantly being discharged out the shooter nozzles. There should be no delay.

Removing the top of the Carter is simple, remove all the screws, remove the metering rod covers and rods, remove the choke pull off rod, disconnect the accelerator pump rod, disconnect the choke to fast idle cam rod on the driver side and lift the lid straight up and rest it upside down to protect the floats and air bleed tubes. Then the pump can be pulled out. Inspect the pump seal as many have described above, and inspect the shooter nozzle to see what numbers are on it which describe its size. Also look at the top and bottom springs on the pump. The bottom spring should be a lot lighter than the top spring. I have recieved rebuild kits that included incorrect springs. Get some pictures and info on the carb and report it here.

Good luck.

Edit: Mikes carburetors provides high quality rebuild kits with quality accelerator pumps. If the pump skirt looks funky on yours you might get by with just ordering a replacement pump from them. Just be sure you have the correct springs for it.

 

[Orig69]

the timing is at 15-16 degrees currently. I did try removing the vacuum advance and plugging the carb but it made no difference. I looked down the carb the best I could as the car is really wide and it seems to squirt fuel properly. Guess the next thing to do is the acc pump.

If the engine does not ping under full throttle then try and advance the ignition timing a little more.

 

[Rishi]

Throttle hesitations or stumbles are among the most challenging problems to solve. And I've learned a great deal over the years solving this semi-common issue.

There are some good tips and advice posted, so far. I'm betting this problem lies within the carburetor, and not the distributor, vacuum advance, engine timing or dwell angle.

When the car previously worked well, and nothing has changed on the vehicle, and the carburetor previously functioned without the stumble, then in my experience, something got dirty or worn out. I recommend you bench-inspect the carb, internally, and confirm it is as clean outside as it is in. Just remove the cover and have a look. Try not to change anything while inspecting. Inspect the accelerator pump plunger, and make sure its in decent shape. During carburetor removal, operate the throttle and watch the fuel squirt out the accelerator pump.

Provided the above is in good order, you can replace the carburetor back onto the engine. I recommend your next check be for a vacuum leak. Don't overlook leaky primary throttle shaft bushings. If there is no obvious vacuum leak when lightly opening and closing the throttle, and the accelerator pump circuit appears to be functioning, then I would begin learning how to check and adjust the carburetor settings. Use a vacuum gauge on this test.

Regarding the holes on the accelerator pump arm. When operating with a factory camshaft and idling near factory specs, use the bottom hole, allowing the longest duration of pump discharge. When operating with a long-duration camshaft and/or at higher idle speeds, move the rod up so it squirts it's load faster.

When you can get the idle to stumble with only a tiny bit of movement at the throttle, be sure to look hard at those throttle shaft bushings for a vacuum leak. Most of these carbs are about 50 years old, and have never been "bushed." The throttle shafts are worn and leak a little bit when operating. Using a vacuum gauge, the vacuum should NOT drop abruptly when gently opening the throttle. If the vacuum varies at idle, simply by jiggling the throttle shaft back and forth (without rotating it), you have a worn bushing problem to solve.

One last point: the accelerator pump operates on a semi-abrupt increase in the throttle. If you open the throttle slowly enough, the pump check ball will redirect fuel flow, and little or nothing comes out the pump nozzle. If you can cause this stumble, even when opening the throttle so slowly no fuel squirts out the nozzle, then it may be argued this problem is unrelated to the accelerator pump or it's discharge timing.

 

[Geoff 2]

Post #26.
Looking at the pic, the mixture screws seem to be backed out a loooooong way. More than I would expect. Have they been adjusted for best idle, or have they been backed out to try & fix the hesitation?

 

[71GTXdragpack]

If the engine does not ping under full throttle then try and advance the ignition timing a little more.

I was going to gradually increase the timing to around 20 degrees or whatever it could take and not ping and start without too much load on the starter.

 

[71GTXdragpack]

Throttle hesitations or stumbles are among the most challenging problems to solve. And I've learned a great deal over the years solving this semi-common issue.

There are some good tips and advice posted, so far. I'm betting this problem lies within the carburetor, and not the distributor, vacuum advance, engine timing or dwell angle.

When the car previously worked well, and nothing has changed on the vehicle, and the carburetor previously functioned without the stumble, then in my experience, something got dirty or worn out. I recommend you bench-inspect the carb, internally, and confirm it is as clean outside as it is in. Just remove the cover and have a look. Try not to change anything while inspecting. Inspect the accelerator pump plunger, and make sure its in decent shape. During carburetor removal, operate the throttle and watch the fuel squirt out the accelerator pump.

Provided the above is in good order, you can replace the carburetor back onto the engine. I recommend your next check be for a vacuum leak. Don't overlook leaky primary throttle shaft bushings. If there is no obvious vacuum leak when lightly opening and closing the throttle, and the accelerator pump circuit appears to be functioning, then I would begin learning how to check and adjust the carburetor settings. Use a vacuum gauge on this test.

Regarding the holes on the accelerator pump arm. When operating with a factory camshaft and idling near factory specs, use the bottom hole, allowing the longest duration of pump discharge. When operating with a long-duration camshaft and/or at higher idle speeds, move the rod up so it squirts it's load faster.

When you can get the idle to stumble with only a tiny bit of movement at the throttle, be sure to look hard at those throttle shaft bushings for a vacuum leak. Most of these carbs are about 50 years old, and have never been "bushed." The throttle shafts are worn and leak a little bit when operating. Using a vacuum gauge, the vacuum should NOT drop abruptly when gently opening the throttle. If the vacuum varies at idle, simply by jiggling the throttle shaft back and forth (without rotating it), you have a worn bushing problem to solve.

One last point: the accelerator pump operates on a semi-abrupt increase in the throttle. If you open the throttle slowly enough, the pump check ball will redirect fuel flow, and little or nothing comes out the pump nozzle. If you can cause this stumble, even when opening the throttle so slowly no fuel squirts out the nozzle, then it may be argued this problem is unrelated to the accelerator pump or it's discharge timing.

amazing response. I will take the time to read it over and follow the steps.

 

[71GTXdragpack]

Post #26.
Looking at the pic, the mixture screws seem to be backed out a loooooong way. More than I would expect. Have they been adjusted for best idle, or have they been backed out to try & fix the hesitation?

I agree it does look odd. Also my idle screw seems to be out a long way also. I did use a vacuum gauge to set the idle mixture to the best possible vacuum.

 

[RJRENTON]

I believe it's an Eddy carb. I moved the rod to the highest level giving the longest throw on the power valve. I adjusted the vacuum by warming the engine, setting the timing, adjusting the idle rpm and adjusting the mixture settings on the carb using a vacuum gauge.

There is no such thing as an "EDDY" carb......do you mean Edelbrock or the Weber facsimile of the origional Carter and whether it's an AFB or AVS. Since you keep referring to the power valve, only Holley uses a power valve. A few pix will be helpful......
BOB RENTON