440 hesitates on light throttle

[71GTXdragpack]

Hi all,
taken me some time but I'm finally driving and enjoying my 71 GTX. During the shakedown drives, I notice a hesitation or bogging of the engine only on light throttle. It disappears as soon as I get on the throttle.
Here is what I've done so far to try and correct with limited success:
1. Removed additional remote fuel filter someone had added inline to the pump. Should I consider changing the vapor separator/filter?
2. Set ignition timing to 12 degrees advance (I know I can go more)
3. Adjusted carb to obtain 18 inches at idle
4. fresh tank of fuel, thinking the leftover fuel from last fall might be causing the hesitation
5. Adjusted power valve to highest setting
5. In the process of changing the plugs. I had no idea 440 were so difficult for access
6. How can I determine if the bogging is fuel related or spark related?

 

[MWbirdLOVER70]

Maybe the accelerator pump diaphram tore or slightly dry rotted. Does give it that primary shot when tipping in

 

[Sam69sat]

Another thing to check is the vacuum advance. I've had a similar issue and plugging the vacuum advance at the carburetor made it go away. Might not be your issue but it's a simple thing to try and eliminate a potential issue.

 

[AR67GTX]

“5. Adjusted power valve to highest setting”

I‘m probably having a brain dump and will regret asking this - but what the heck is the power valve? I’m familiar with Holley power valves but “adjustable“ and “highest setting” don’t compute.

I‘ll second it sounds like an accelerator pump issue. If a Carter, the synthetic accelerator pump seals have been know to fail early. The leather ones are considered best. whether a Holley or Carter, check the front throat for sign of accelerator pump spray immediately on moving the throttle.

 

[Suregrip391]

undo the vacuum advance at the carb and plug it at the carb ( should be hooked up to your Timed or ported carb port. Not your straight manifold vacuum. Drive the car and see how it acts. If the problem goes away, your issue is in the vacuum advance part of your distributor. I just went through this and Ray and Halifax rebuilt my distributor. I had a second distributor laying around and once I swapped them out, the car ran 110 percent better! Remember, ignition before carburation!

 

[Bee1971]

Agree on the factory leather type accelerator pump dried out

But never stated if the carb is the factory Carter AVS or something else

 

[Doorkicker]

accelerator pump and/or discharge size too small.

 

[Rishi]

I vote accelerator pump. that's what it was for me, more than once. For some reason, heavy foot (probably because of the kick-down) doesn't do it as much as light throttle changes.

 

[hunt2elk]

Holley carb? Have you tried different accelerator pump cams and squirters?

 

[Geoff 2]

[1] Highest power valve? Do you mean a Holley carb, with the PV having the highest number?
[2] Or a good carb like a Carter, stiffest piston springs?
[3] How/what did you adjust to get 18" of vac at idle?

With either: operate the throttle lever & see if the acc pump nozzle squirts fuel.

 

[71GTXdragpack]

[1] Highest power valve? Do you mean a Holley carb, with the PV having the highest number?
[2] Or a good carb like a Carter, stiffest piston springs?
[3] How/what did you adjust to get 18" of vac at idle?

With either: operate the throttle lever & see if the acc pump nozzle squirts fuel.

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.

 

[71GTXdragpack]

undo the vacuum advance at the carb and plug it at the carb ( should be hooked up to your Timed or ported carb port. Not your straight manifold vacuum. Drive the car and see how it acts. If the problem goes away, your issue is in the vacuum advance part of your distributor. I just went through this and Ray and Halifax rebuilt my distributor. I had a second distributor laying around and once I swapped them out, the car ran 110 percent better! Remember, ignition before carburation!

I'll try blocking the vacuum advance and see if the hesitation goes away.

 

[Doorkicker]

You know.. I'm re-reading the original post and now I have a ton of questions... some others have posted as well... so let's get them all in one place shall we?

1 - What carb? Holley, Eddie, etc. ? Size, mechanical or vac secondaries, double pumper or single?

2 - 12 degree initial timing? What is total timing set at?

3 - How did you set 18 vac? Tons of questions here... If you did so just using the idle mixture screws you're AFR might be off. Any vac leaks? Did you disconnect the vac adv. to distr.? Where did you attach the vac gauge, etc. Can you share the cam basics... just lift, duration, and lsa would be helpful.

4 - You refer to the power valve, so assuming a Holley or clone? Not sure what's meant by highest setting... because they come in vac rating measurements. If you're running 18 vac that would indicate an 8.5 valve is recommended, which is 2 steps up from stock. What is the number imprinted on the power valve?

5 - What size is the squirter? There's a tiny number on it... like 28 or 31? It's officially the "accelerator nozzle". Also, did you check the check needle isn't stuck? Remove the squirter and there's a needle valve in there... make sure it's not gummed up.

6 - When does it bog? Off the line or jamming on it while going 30-50 mph? If it's one or the other it could be a fuel pump kinda thing... even with good fuel press. What is your fuel press? BTW... I'm assuming the engine is up to temp... if it's doing this while cold... let it warm up to operating temp and then make it do it.

7 - Accelerator pump settings... the pump actuator could be out of adjustment. And/or the pump actuator cam could be broken or simply the wrong one.

8 - Your fuel or spark related question... unless you're backfiring out the carb, I'd focus on fuel for now. However, I think your timing is potentially contributing. Nevertheless, with that in mind what is your ign system? Type of distributor, type of coil, and type of ign (ign box, ready to run, points, stock controller, etc.)

Basically, a ton of stuff can cause what you're describing. But it's rarely a hard fix.. just a lot of little things and adjustments.

 

[71GTXdragpack]

You know.. I'm re-reading the original post and now I have a ton of questions... some others have posted as well... so let's get them all in one place shall we?

1 - What carb? Holley, Eddie, etc. ? Size, mechanical or vac secondaries, double pumper or single? Believe it's an Eddy carb with vac secondaries

2 - 12 degree initial timing? What is total timing set at? I've only set initial timing, haven't checked total timing yet

3 - How did you set 18 vac? Tons of questions here... If you did so just using the idle mixture screws you're AFR might be off. Any vac leaks? Did you disconnect the vac adv. to distr.? Where did you attach the vac gauge, etc. Can you share the cam basics... just lift, duration, and lsa would be helpful. No obvious vacuum leaks, I did disconnect the vac adv. I attached the vac gauge at a port at the back of the intake. Not sure of cam as I bought the car about a 1.5 ago.

4 - You refer to the power valve, so assuming a Holley or clone? Not sure what's meant by highest setting... because they come in vac rating measurements. If you're running 18 vac that would indicate an 8.5 valve is recommended, which is 2 steps up from stock. What is the number imprinted on the power valve? Eddy carb which have an power valve which can be adjusted by moving the position of the rod on the bracket.

5 - What size is the squirter? There's a tiny number on it... like 28 or 31? It's officially the "accelerator nozzle". Also, did you check the check needle isn't stuck? Remove the squirter and there's a needle valve in there... make sure it's not gummed up. I have not check but idle and WOT is no issue

6 - When does it bog? Off the line or jamming on it while going 30-50 mph? If it's one or the other it could be a fuel pump kinda thing... even with good fuel press. What is your fuel press? BTW... I'm assuming the engine is up to temp... if it's doing this while cold... let it warm up to operating temp and then make it do it. It bogs at light throttle only, when anything more than light throttle, there is no bog

7 - Accelerator pump settings... the pump actuator could be out of adjustment. And/or the pump actuator cam could be broken or simply the wrong one.

8 - Your fuel or spark related question... unless you're backfiring out the carb, I'd focus on fuel for now. However, I think your timing is potentially contributing. Nevertheless, with that in mind what is your ign system? Type of distributor, type of coil, and type of ign (ign box, ready to run, points, stock controller, etc.) The car currently has stock points type ignition with stock coil.

Basically, a ton of stuff can cause what you're describing. But it's rarely a hard fix.. just a lot of little things and adjustments.

Hello,
I'll try to answer the questions to my best ability. Please see my answers above.

 

[Doorkicker]

Cool! Thanks... I'll try to respond to your notes.

1 - Perfect. Thanks. Eddie it is.

2 - I only ask because there could be a situation where the timing is not advancing quickly enough or too much. Depending on your setup, I would just double check. It could be as easy as checking the springs and the weights in the dist. (assuming it's mechanical, of course, just as an example)

3 - Ok... so vac checked pretty well and the cam info would have been helpful from a total vac at idle, but not critical.

4 - Ok... as you know there are four parts to that... jet, metering rod, spring and piston. Did you happen to change the spring or the rod? Or did you change the jet? Although Holley is different, there are several circuits to do the same thing, Eddie you can tune a lot with just those four devices... each will have a wide range of affects on performance. So, it would help to know what you have and changed.

5 - My question is slightly moot now... wrong carb But... like you said... nothing gummed up there.

6 - Very helpful! So, bogs at the very initial throttle input... got it.

7 - I would definitely pop the top off and run through some checks on the accelerator pump and check valve. Here's a good vid:

8 - Ok, very helpful. However, now that we know it's just on initial throttle input... not so sure about the ign. I would double check the gap on the points and verify the dist. points cam isn't loose or warn. Also, may want to check the capacitor... at initial it could be light on discharging. Just a guess. Still think you're dealing with a fuel issue (or perhaps a timing/advance issue)... but worth a check on the points gap and cap.

 

[71GTXdragpack]

there were some questions regarding adjusting the power valve. The diagram shows the accelerator pump rod and I simply adjusted it to the top level to extend the travel to maximum.

 

[71GTXdragpack]

Cool! Thanks... I'll try to respond to your notes.

1 - Perfect. Thanks. Eddie it is.

2 - I only ask because there could be a situation where the timing is not advancing quickly enough or too much. Depending on your setup, I would just double check. It could be as easy as checking the springs and the weights in the dist. (assuming it's mechanical, of course, just as an example)

3 - Ok... so vac checked pretty well and the cam info would have been helpful from a total vac at idle, but not critical.

4 - Ok... as you know there are four parts to that... jet, metering rod, spring and piston. Did you happen to change the spring or the rod? Or did you change the jet? Although Holley is different, there are several circuits to do the same thing, Eddie you can tune a lot with just those four devices... each will have a wide range of affects on performance. So, it would help to know what you have and changed.

5 - My question is slightly moot now... wrong carb But... like you said... nothing gummed up there.

6 - Very helpful! So, bogs at the very initial throttle input... got it.

7 - I would definitely pop the top off and run through some checks on the accelerator pump and check valve. Here's a good vid:

8 - Ok, very helpful. However, now that we know it's just on initial throttle input... not so sure about the ign. I would double check the gap on the points and verify the dist. points cam isn't loose or warn. Also, may want to check the capacitor... at initial it could be light on discharging. Just a guess. Still think you're dealing with a fuel issue (or perhaps a timing/advance issue)... but worth a check on the points gap and cap.

Thank you for all the tips and advise. I'm re-learing a lot of things and am very thankful for your knowledge.

 

[Bee1971]

“I believe it's an Eddy carb”

You 100% positive ?

Picture is an Carter AVS that you are showing

And there is a huge difference between accelerator pumps and material

 

[71GTXdragpack]

“I believe it's an Eddy carb”

You 100% positive ?

Picture is an Carter AVS that you are showing

And there is a huge difference between accelerator pumps and material

sorry you're correct!

 

[Bee1971]

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