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Discussion Starter #1
Hey Guys!

I am looking for some advice on where to start attacking this problem. The issue is:

When the car is warm, at cruising speed >30mph, when coasting and getting back into the throttle - my car will miss/hesitate at the first touch of the throttle. After a second, it picks up and runs/accelerates fine. The car will not reproduce this in park at idle. If the accelerator is mashed at speed, it does not hesitate. It seems to only be a problem at "light touch" while coasting.

Any thoughts out there? The car is a 65 conv but I have a 302 block. Edelbrock performer intake, GT40P heads, Edelbrock performer carb.

I have tried adjusting the accelerator pump linkage... but it does not seem to make a difference.

Any ideas I can try would be appreciated! Thanks! Jim.
 

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Simple answer: your engine needs some tuning.

Which model Edelbrock carb?
Probably wouldn’t hurt to get a tuning kit. Or at the very least, a set of step up springs for the metering rods.

What’s your ignition timing set at?
Is the distributor using vacuum advance?
If so, ported or manifold vacuum?
 

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Discussion Starter #5
Thanks for the replies.

MrFlash - The carb is a 1406, 600 cfm. The distributor is running vacuum advance using the manifold vacuum. Timing is at 12 deg. Does this all sound reasonable for this set up?

Forestg - Thank you I will try that and see if it helps.

Mustang#1 - Thanks! It has been a looooong process. haa haa.
 

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I would try advancing the timing around 2-4 degrees. Make sure your vacuum advance is not leaking too.
 

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Fighting a little with this myself; my idle is fine, and acceleration is fine, but slight throttle leads to lots of jerkiness. I thought I had it ironed out when I relocated my coil, but it's back. Not as bad (car was actually dying on me before, even idling), but I did fiddle with the timing slightly and readjust my points.

Since mine does it in all gears at all speeds (does not falter cracking throttle at idle in neutral) and only at that magic throttle crack position it's not really RPM related, but rather load/throttle related. I'm thinking timing/carb or a combination therein.
 

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It sounds like the idle mixture circuit and transition circuit of the carb.

Typically when the idle circuit is not set right, you will be able to flip over the carb and see that the butterflies are cracked too far open.
if that's the case, then when you open the throttle, the carb is not getting the correct signal.

In holley's it would be the power valve, then main jets.

Since in a lot of cases, when the butterflies are open too far after idle, when you open the throttle, there is not enough change in the vacuum signal that is sent to the power valve, so the carb/car is "waiting" for the main jets.

Hence the hesitation

So I haven't had Edelbrock carbs for quite some time. Sounds like the step up spring or pump calibration.

With a tune problem, you would want to go through the whole carb depending on how old the system is.

The transition side is the trickiest to set up, but well worth the time, to have a truly responsive engine. I can't tell you how many years I've been in cars that had that hesitation or bog
 

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Driving into work it was back to dying today, even at idle. After going through the carb (and only finding a slight float adjustment needed and soldering a couple holes in a flooded brass float......), I deduced it must be ignition/electrical related. These carbs run so well when set up properly, I couldn't fathom it being caused by fuel; not as bad as it was knocking and jerking. It was surprisingly violent.

Sure enough, after finding my inline spark detector (worth its weight in gold), I noticed when the engine starts to stumble the spark totally disappears. Cap/rotor, plugs, wires are all good. Coil ohms out in spec, but I need to do some more troubleshooting. Getting ~7 volts at the + side at the coil in the run position and battery voltage when not hooked to the coil. Slight voltage drop of 0.15 volts at the negative side of the coil to ground, so need to sniff around there a bit more.

So I either have an intermittent 12v connection from the ignition switch resistance wire, or something is weird with the points/coil. Was planning on going to a Pertronix III with their coil anyway, but I'm going to iron her out with the points first.

Long story short, it still comes back to the big three things when you have a problem: Air, spark, and fuel. Will keep posted on progress after work tomorrow; I'm done for the day and I'm going to hang with my friend Jim Beam. :)
 

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Edelbrock carbs are known for heat soak issues. I'd tray a nice insulating base gasket and/or a phenolic spacer before going too far.
 

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Nice choice in engine! I'm running a GT40P in my 66 as well. 5.0 Mustang cam, Wieand Stealth and a 600 Edelbrock as well. No issues. The difference is I have the manual choke 1405. The other difference between choke style is calibration. The 1406 is just too lean. It's intended to me more of a emissions style carb. Look up the metering rods, jets and PV spring to that of the 1405 and you'll be fine

On timing, the P head has a very efficient combustion chamber. You need only 28° to 30° total mechanical. Set initial timing to 10°
 

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Nittany Lions? On second thought I think you need a tunnel ram with dual Holley Dominators. My daughter is going to Pittsburgh for her OTD.
 

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I have pretty much the same symptoms as stanglocal with a 600cfm Holley Double Pumper with mechanical secondaries. I have tried adjusting the timing and that doesn't seem to help. I leaned out the idle mixuture a little and that did help some, but didn't totally get rid of the problem. I swapped in a 5.5 power valve a while back when I tore the carb apart to clean it and install new gaskets. With the Edelbrock Performer RPM cam and intake I am only pulling around 11 vacuum so it should be fine. I also installed the top facing adjustment screw for the rear blades so I can adjust front and rear without taking the carb off. Anyway, I already have an MSD box, MSD billet distributor, MSD plug wires and MSD coil, so I doubt it is a spark issue. I just can't figure out how to dial this thing in... I tried setting up an appointment with a local tuner who is really good, but haven't been able to get an appointment I can make yet due to work schedule.
 

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I have pretty much the same symptoms as stanglocal with a 600cfm Holley Double Pumper with mechanical secondaries. I have tried adjusting the timing and that doesn't seem to help. I leaned out the idle mixuture a little and that did help some, but didn't totally get rid of the problem. I swapped in a 5.5 power valve a while back when I tore the carb apart to clean it and install new gaskets. With the Edelbrock Performer RPM cam and intake I am only pulling around 11 vacuum so it should be fine. I also installed the top facing adjustment screw for the rear blades so I can adjust front and rear without taking the carb off. Anyway, I already have an MSD box, MSD billet distributor, MSD plug wires and MSD coil, so I doubt it is a spark issue. I just can't figure out how to dial this thing in... I tried setting up an appointment with a local tuner who is really good, but haven't been able to get an appointment I can make yet due to work schedule.
With a Holley, a stumble at tip-in is usually an accelerator pump issue. You might need either a more aggressive pump cam, or a larger discharge nozzle.

 

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Thanks, I forgot to mention that I have adjusted the spring tension for the pumps, but I guess it could be the wrong size squirter or cam.

Sent from my Moto G (5) Plus using Tapatalk
 

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Driving into work it was back to dying today, even at idle. After going through the carb (and only finding a slight float adjustment needed and soldering a couple holes in a flooded brass float......), I deduced it must be ignition/electrical related. These carbs run so well when set up properly, I couldn't fathom it being caused by fuel; not as bad as it was knocking and jerking. It was surprisingly violent.

Sure enough, after finding my inline spark detector (worth its weight in gold), I noticed when the engine starts to stumble the spark totally disappears. Cap/rotor, plugs, wires are all good. Coil ohms out in spec, but I need to do some more troubleshooting. Getting ~7 volts at the + side at the coil in the run position and battery voltage when not hooked to the coil. Slight voltage drop of 0.15 volts at the negative side of the coil to ground, so need to sniff around there a bit more.

So I either have an intermittent 12v connection from the ignition switch resistance wire, or something is weird with the points/coil. Was planning on going to a Pertronix III with their coil anyway, but I'm going to iron her out with the points first.

Long story short, it still comes back to the big three things when you have a problem: Air, spark, and fuel. Will keep posted on progress after work tomorrow; I'm done for the day and I'm going to hang with my friend Jim Beam. :)
Update on my stumbling issue: Twas the condenser in the distributor. Failing intermittently, the arching hadn't gone long enough to be visibly noticeable inside the cap or on the points yet. For $3, it was a swap and see thing, and if it didn't solve the issue, I would have a spare in the glovebox. Also had a jumper wire ready to run 12v to the coil to bypass the ignition switch and resistance wire. Didn't need to go there though.

Long story short, swapped it out and everything is back to normal. Noticed a small amount of goo at the wire end of the condenser I replaced, so maybe the electrolytic paste was oozing out or somehow water had gotten in there. Now I have a condenser with a lifetime warranty and I'll never have to buy one again. :smile2:
 
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