Surge problem at speed

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davidcribbs

davidcribbs

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I have been struggling for a month or so trying to figure out a performance issue. I have a '67 Dart with a 360 LA engine. I had some electrical work about 6 weeks ago due to massive drains on my battery. During the work the distributor got fried. The shop doing the work replaced the distributor (ignition switched to electronic ignition 6 years ago). Since I have gotten the car back the electrical system is great, but when I accelerate heavily it sputters kinda like it is not firing correctly. At speed on the highway it will surge periodically, almost like it missfires, then it is fine. Literally just a quick misstep, then all is good. It seems to do this less at 70 miles an hour, which is about 3k on the tach. I found some gunk in the carb, cleaned and rebuilt the carb, still sputtered, but better. Finally ended up replacing the carb, filter and fuel pump, and still sputtering. Took it to a shop and they changed the spark plug wires, still sputtering. I am thinking that the distributor that replaced the one that got fried is not firing correctly. I am thinking about switching to one of the Petronix billet distributors to see if that fixes the problem, or should I be looking elsewhere? Any help would be appreciated, or I have to break out the blow torch.
 
go back to points and try it. Should be about a $15 experiment and youll have a spare in the trunk if the HEI/ECU/pick up fails again. electronic distributors are super simple but trying to figure out a random miss is far easier with an uber simple Kettering (points) distributor
 
Have you check the reluctor gap in the distributor? Also, to just replace he distributor is pretty generic. What is you static and total timing? Is the vacuum advance hooked up and have you disconnected it to see if you issue goes away? Have you tried a different ignition box and is the case to yours grounded really well?

The Pertronix has a janky way to adjust the mechanical advance. If you want an easy to adjust drop in the Jegs billet distributor is pretty good considering the price and it uses the stock cap. A member here, halifaxhops sells curved stock distributors as well if you don't to mess with setting one up yourself.

[FOR SALE] - Mopar distributors
 
Vacuum advance connected to the wrong port...
Disconnect and plug vacuum advance and try it..
Check your timing at idle and at three grand plus...
 
davidcribbs said:
I have been struggling for a month .
Click to expand...

As detailed as this was, you gave no information as to the type of ignition system. Is this Mopar ECU, Pertronix, MSD or some other?

One of the first things I'd do is make a few test runs with the ignition hot wired in order to bypass the wiring harness and ignition switch. If the system uses a ballast resistor, do not bypass that. "Rig" a clean safe way to "hot wire" the ignition and make some test runs

Depending on the type of ignition, there are some tests you can do, but we need to know what type the ignition is

It's possible EG, that this could be as simple as a loose / bad connection, or a tach wire shorting /"pinched" on the way to the tach.
 
I had a similar issue and it turned out to be the Rotor. My rotor was not that old. Sometimes new fails as well. Seen it happen to a friends chevy truck once. New out of the box. Take a close look at it .
 
Oh also, 67dart273 will help you systematicly get it fiqured out for sure . He saved my head from exploding once .
 
I think you've found the issue. You said it improved each time you messed with the carburetor. That tells me it's a fuel issue. Have you ever removed and cleaned the fuel tank? You can rebuild the carburetor a thousand times and unless you clean the SOURCE, you will never fix it.
 
I was thinking fuel also or I was really thinking "are you sure it is electrical?" LOL! I had an issue with "vapor lock" it turned out the fuel line was too close to the header on the right frame rail. I pulled it tighter to the rail with mechanics wire and it never happened again. Mine would act like it was out of gas,shut down. id get it off the road,wait 20 minutes and fire it up and go. I would thinlk"air" in the fuel line would cause surge or even erratic fuel pressure.

As an aside, whay are people going with pertronix? what is wrong with MP electronic ignition? I have heard the modules are junk now maybe they always were:) Mine work ok.Orange box.
 
davidcribbs said:
when I accelerate heavily it sputters kinda like it is not firing correctly. At speed on the highway it will surge periodically, almost like it missfires, then it is fine. Literally just a quick misstep, then all is good. It seems to do this less at 70 miles an hour, which is about 3k on the tach.
Click to expand...

You're mixing me up;
I see three problems right?
1) "when I accelerate heavily it sputters kinda like it is not firing correctly."
2) At speed on the highway it will surge periodically,
3) almost like it missfires, then it is fine. Literally just a quick misstep, then all is good.
4) seems to do this less at 70 miles an hour, which is about 3k on the tach

My guess is your plugs are overheating, and/or your coil is weak, AND on the low-speed circuit, yur a lil lean or running retarded low-speed AND cruise-timing.

Start by inspecting the plugs.
If I'm right, they will be almost pure white with lil patches of dark glaze on them. If they're not as described, I'm just wrong. lol.

But before you do anything, defeat the vacuum advance, and put a strobe-lite on it, then slowly rev it up while watching the timing mark on the balancer. You should see that it moves smoothly (see note 2)beginning at about 1000 rpm and finishing at 3600rpm or maybe a lil less.
Then re-install the vacuum line to the SPARKPORT, and repeat,looking for same smoothness. Rev it to your cruise-rpm of ~3000, and your engine will be wanting about 48 degrees of cruise-timing there. See whatchagot.

Next, with the light still on it, rev it up to about 1800, and hold it there, Then with the light strobing, whack the throttle open, while watching the strobe. If the strobe hesitates, guess what, your coil failed to keep up. You will have to figure out why.

Finally;
With the transfer-slot to idle-discharge port ratio synced up; (see note 1)
Clamp the power brake booster hose off, and make sure the PCV is working properly, and is plumbed correctly to just under the primary blades. Re-install the Vacuum advance if off. Next rev it up to ~2200 and put the throttle up on the nearest fast-idle step. Next, adjust the mixture screws for highest rpm. While there, check the timing. Your engine will like 40 to 45 degrees, but good luck giving her that much. Make a note of what yours has.
Return the engine to idle. Note the rpm, then, unclamp the booster hose and note any change in rpm. A momentary dip is normal, but it should come right back into line in just a few seconds. If it does not, then it is leaking air and you will have to fix that.
Next clamp off the fuel supply line, and wait.
A) After maybe 30 seconds, if the fuel level is about right, the rpm will start to rise, reach a plateau, hover there for a few seconds, then rapidly decline
B) If the level is too low, the rpm will start to fall immediately
C) If the level is too high, the rpm will start to rise almost immediately, and climb and climb for a long time, before turning around.
As soon as the rpm starts to drop, unclamp the fuel line and let the idle-rpm stabilize.
If your engine reacts as at B or C, then you will have to check the fuel level in the bowls.
HOWEVER,
If your Transfer port sync is out to lunch you will have to back up the bus and get that right first. Then start over.

Note 1
At idle, your carb is supposed to be spewing fuel from exactly two places only, namely; the transfer slots and the idle discharge ports. If your throttle blades are too far up the transfer slots, you will have to take fuel away using the ports. If your blades are not far enough up the transfers, you will have to crank the mixture screws out towards rich until you run out of adjustability.
The ideal place will have the mixture screws open to about 50% of their working range.
So set them to 50%. Then open or close the throttle blades to supply the balance of the fuel. If your idle-rpm gets wonky, you will have to change the timing to bring it back into a reasonable place. And then you will have to fine-tune the throttle blades again.

You will know when the sync is right by the following;
1) the idle rpm is in a window of about 650 in gear, no more than 100 rpm higher in neutral.
2) the engine does not want to stall on the Neutral to Drive shift, nor bang into gear.
3) freedom from a tip-in sag. That us to say, when you apply throttle GENTLY from idle, in gear, to take off gently; the car does not momentarily hesitate.
4) with the secondaries closed up tight but NOT sticking, and engine at idle, she should be slightly rich. Prove it by slowly restricting the airhorn. If the rpm flares up, she is lean.

You didn't mention having a cam so I'll skip that.
With a factory cam, this will require an idle timing of about 8 to 10, no more than 12 degrees. I would start on the low end.
When yur done, your power-timing needs to be in a range that does not cause detonation. A suggested starting point for a stock-type engine is 34* at 3400 rpm; with the Vcan defeated.

Note 2
If the strobe jumps around wildly from retard to advance AND she drops sparks; then
if you have a magnetic pick-up, the polarity is reversed.
If the strobe drops sparks only, check your reluctor gap.

Oh I almost forgot, make sure your fuel-tank vent is working.
 
Last edited:
As suggested by others, I would disconnect the VA. The way it works in Chrys dizzies, with it's over-centering action, might cause reluctor to p/up coil contact, which results in no spark on that cyl. You say the dist has been replaced. Make sure the shaft is tight in the top bush, to avoid the contact mentioned above.
 
pishta said:
go back to points and try it. Should be about a $15 experiment and youll have a spare in the trunk if the HEI/ECU/pick up fails again. electronic distributors are super simple but trying to figure out a random miss is far easier with an uber simple Kettering (points) distributor
Click to expand...
Great idea, thanks. I will give it a shot.
 
dano said:
Have you check the reluctor gap in the distributor? Also, to just replace he distributor is pretty generic. What is you static and total timing? Is the vacuum advance hooked up and have you disconnected it to see if you issue goes away? Have you tried a different ignition box and is the case to yours grounded really well?

The Pertronix has a janky way to adjust the mechanical advance. If you want an easy to adjust drop in the Jegs billet distributor is pretty good considering the price and it uses the stock cap. A member here, halifaxhops sells curved stock distributors as well if you don't to mess with setting one up yourself.

[FOR SALE] - Mopar distributors
Click to expand...
I will take a look at the timing, but I probably failed to mention that the distributor and previous carburetor were in the car for 6 years together and running well, prior to it being fried during the charging system work. Vacuum advance is hooked up, and was with the previous carburetor as well. The ignition was one of the cheap Proform setups (although it worked pretty well for 6 years) originally when I switched from points to electronic. I will check to see if the issue goes away by disconnecting the vacuum advance.

As far as the Petronix goes, I was looking at the Flame-Thrower vacuum advanced distributor. I will check out the Jegs unit though, if I find the distributor is the likely culprit. Thanks for the info.
 
j par said:
Vacuum advance connected to the wrong port...
Disconnect and plug vacuum advance and try it..
Check your timing at idle and at three grand plus...
Click to expand...
I will go through the specs again, and make sure all is good.
 
67Dart273 said:
As detailed as this was, you gave no information as to the type of ignition system. Is this Mopar ECU, Pertronix, MSD or some other?

One of the first things I'd do is make a few test runs with the ignition hot wired in order to bypass the wiring harness and ignition switch. If the system uses a ballast resistor, do not bypass that. "Rig" a clean safe way to "hot wire" the ignition and make some test runs

Depending on the type of ignition, there are some tests you can do, but we need to know what type the ignition is

It's possible EG, that this could be as simple as a loose / bad connection, or a tach wire shorting /"pinched" on the way to the tach.
Click to expand...
The ignition was the Proform ignition, and it had been in the car for 6 years, and even though it is lower dollar, actually worked pretty well.

I hadn't thought of a short, but will try and eliminate that as a culprit.
 
Kendog 170 said:
I had a similar issue and it turned out to be the Rotor. My rotor was not that old. Sometimes new fails as well. Seen it happen to a friends chevy truck once. New out of the box. Take a close look at it .
Click to expand...
Thanks, I will break the distributor down this weekend and see if something glaring sticks out.
 
The things changed were the distributor and the control unit.
Now its trailor hitching.
New distributor probably has very different curve and characterists.
Or they gave it too much initial.
Now its trailer hitching. Yes it could be too much timing in certain rpm and load conditions. Since the conditions are light load vac advance is a part of that.

Replace the magnetic pickup in the old one and try that, and or try the points distributor.

The only way to know what the timing looks like in an aftermarket distributor will to measure the timing at various rpms and then plot it.
 
If its actually surging while driving steady. That is the engine revs up and then dies, then catches when you lift off the throttle slightly - that's lean.
 
Mattax said:
If its actually surging while driving steady. That is the engine revs up and then dies, then catches when you lift off the throttle slightly - that's lean.
Click to expand...

Yeah well....you can lead a horse to water.....
 
AJ/FormS said:
You're mixing me up;
I see three problems right?
1) "when I accelerate heavily it sputters kinda like it is not firing correctly."
2) At speed on the highway it will surge periodically,
3) almost like it missfires, then it is fine. Literally just a quick misstep, then all is good.
4) seems to do this less at 70 miles an hour, which is about 3k on the tach

My guess is your plugs are overheating, and/or your coil is weak, AND on the low-speed circuit, yur a lil lean or running retarded low-speed AND cruise-timing.

Start by inspecting the plugs.
If I'm right, they will be almost pure white with lil patches of dark glaze on them. If they're not as described, I'm just wrong. lol.

But before you do anything, defeat the vacuum advance, and put a strobe-lite on it, then slowly rev it up while watching the timing mark on the balancer. You should see that it moves smoothly (see note 2)beginning at about 1000 rpm and finishing at 3600rpm or maybe a lil less.
Then re-install the vacuum line to the SPARKPORT, and repeat,looking for same smoothness. Rev it to your cruise-rpm of ~3000, and your engine will be wanting about 48 degrees of cruise-timing there. See whatchagot.

Next, with the light still on it, rev it up to about 1800, and hold it there, Then with the light strobing, whack the throttle open, while watching the strobe. If the strobe hesitates, guess what, your coil failed to keep up. You will have to figure out why.

Finally;
With the transfer-slot to idle-discharge port ratio synced up; (see note 1)
Clamp the power brake booster hose off, and make sure the PCV is working properly, and is plumbed correctly to just under the primary blades. Re-install the Vacuum advance if off. Next rev it up to ~2200 and put the throttle up on the nearest fast-idle step. Next, adjust the mixture screws for highest rpm. While there, check the timing. Your engine will like 40 to 45 degrees, but good luck giving her that much. Make a note of what yours has.
Return the engine to idle. Note the rpm, then, unclamp the booster hose and note any change in rpm. A momentary dip is normal, but it should come right back into line in just a few seconds. If it does not, then it is leaking air and you will have to fix that.
Next clamp off the fuel supply line, and wait.
A) After maybe 30 seconds, if the fuel level is about right, the rpm will start to rise, reach a plateau, hover there for a few seconds, then rapidly decline
B) If the level is too low, the rpm will start to fall immediately
C) If the level is too high, the rpm will start to rise almost immediately, and climb and climb for a long time, before turning around.
As soon as the rpm starts to drop, unclamp the fuel line and let the idle-rpm stabilize.
If your engine reacts as at B or C, then you will have to check the fuel level in the bowls.
HOWEVER,
If your Transfer port sync is out to lunch you will have to back up the bus and get that right first. Then start over.

Note 1
At idle, your carb is supposed to be spewing fuel from exactly two places only, namely; the transfer slots and the idle discharge ports. If your throttle blades are too far up the transfer slots, you will have to take fuel away using the ports. If your blades are not far enough up the transfers, you will have to crank the mixture screws out towards rich until you run out of adjustability.
The ideal place will have the mixture screws open to about 50% of their working range.
So set them to 50%. Then open or close the throttle blades to supply the balance of the fuel. If your idle-rpm gets wonky, you will have to change the timing to bring it back into a reasonable place. And then you will have to fine-tune the throttle blades again.

You will know when the sync is right by the following;
1) the idle rpm is in a window of about 650 in gear, no more than 100 rpm higher in neutral.
2) the engine does not want to stall on the Neutral to Drive shift, nor bang into gear.
3) freedom from a tip-in sag. That us to say, when you apply throttle GENTLY from idle, in gear, to take off gently; the car does not momentarily hesitate.
4) with the secondaries closed up tight but NOT sticking, and engine at idle, she should be slightly rich. Prove it by slowly restricting the airhorn. If the rpm flares up, she is lean.

You didn't mention having a cam so I'll skip that.
With a factory cam, this will require an idle timing of about 8 to 10, no more than 12 degrees. I would start on the low end.
When yur done, your power-timing needs to be in a range that does not cause detonation. A suggested starting point for a stock-type engine is 34* at 3400 rpm; with the Vcan defeated.

Note 2
If the strobe jumps around wildly from retard to advance AND she drops sparks; then
if you have a magnetic pick-up, the polarity is reversed.
If the strobe drops sparks only, check your reluctor gap.

Oh I almost forgot, make sure your fuel-tank vent is working.
Click to expand...


Thanks again for your feedback. This thread helped a ton.

After I went through a lot of what you had recommended, once I took off the distributor cap the main issue was glaring. The contact points on the cap were burnt badly. The were blackened, and jagged. I ended up ordering a new distributor, control module, coil, and plugs using the Summit billet distributor and Autolite 65's. This alleviated the two issues I had mentioned regarding the surging at speed, and the stuttering when accelerating hard.

I adjusted the timing, although the car seemed to run better at almost 15 degrees initial timing, which according to your thread sounds a little high? Since I didn't build the engine, I am not sure if it has a cam or not. I did plug the vacuum line when timing it, but that sounds like quite a bit of initial timing. No detonations, and seemed like it wanted more. Any thoughts?

After I timed it I worked on the floats, and air fuel mixture, until I got the highest vacuum reading, but now the car has bog immediately when I accelerate. Once I back off on the accelerator it runs good, and has no stutter or stumble. It does this when hot & cold. My thought is that the carb is too lean, is that a place you would start to look? The fuel set-up on this is the Edelbrock mechanical fuel pump, run an Earl's filter inline, and the Holley Brawler 570 carburetor.

Thanks again for the detailed places to look previously.
 
Dartswinger70 said:
I was thinking fuel also or I was really thinking "are you sure it is electrical?" LOL! I had an issue with "vapor lock" it turned out the fuel line was too close to the header on the right frame rail. I pulled it tighter to the rail with mechanics wire and it never happened again. Mine would act like it was out of gas,shut down. id get it off the road,wait 20 minutes and fire it up and go. I would thinlk"air" in the fuel line would cause surge or even erratic fuel pressure.

As an aside, whay are people going with pertronix? what is wrong with MP electronic ignition? I have heard the modules are junk now maybe they always were:) Mine work ok.Orange box.
Click to expand...

PETRONICS HAS A SET UP THAT WILL FIRE MUTPLE TIMES THU OUT THE RPM RANGE TO 10,000 RPM !
 
pishta said:
go back to points and try it. Should be about a $15 experiment and youll have a spare in the trunk if the HEI/ECU/pick up fails again. electronic distributors are super simple but trying to figure out a random miss is far easier with an uber simple Kettering (points) distributor
Click to expand...

Yes, exactly what I was just thinking. Pop a points distributor into it, they run nice on their own. Great for diagnostics.

I use the points distributor on my engines on the run stand, one less thing to go wrong on first start ups and break ins.
 
When were the spark plugs last changed, 6 yrs ago ?
If so, change them, and show us some good pix of tne old ones .
 
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