440 "lunging" at low speed

Posted By: 70VERT

440 "lunging" at low speed - 08/26/14 04:51 AM

My 70 Plymouth 440 (4 speed) has been "lunging" when I coast at low speeds. It idles fine and runs out great through the gears. Only time I notice it is when I am 2,3, or 4th and just kinda coasting at low speeds.....440, Holley 750 Street Avenger,stock heads, Edelbrock Performer manifold and Hughes Whiplash cam. Can you guys give me some advice on what might be going on here and how to straighten it out? Thanx

Posted By: feets

Re: 440 "lunging" at low speed - 08/26/14 05:01 AM

Are you down around idle when this happens?

Posted By: Pacnorthcuda

Re: 440 "lunging" at low speed - 08/26/14 05:04 AM

Advice??? Yea..you're lugging the crap out of it. Downshift.

Posted By: pushbutton

Re: 440 "lunging" at low speed - 08/26/14 02:04 PM

Quote:

My 70 Plymouth 440 (4 speed) has been "lunging" when I coast at low speeds. It idles fine and runs out great through the gears. Only time I notice it is when I am 2,3, or 4th and just kinda coasting at low speeds.....440, Holley 750 Street Avenger,stock heads, Edelbrock Performer manifold and Hughes Whiplash cam. Can you guys give me some advice on what might be going on here and how to straighten it out? Thanx

Do you have the vac advance hooked up? If you do try disconnecting and plugging the hose. See if it helps.

Posted By: RapidRobert

Re: 440 "lunging" at low speed - 08/26/14 02:59 PM

Clarify the lunging: are you coasting down with foot off of the pedal. Are you at a steady speed. what RPM/how much throttle (load/in hg)

Posted By: Cab_Burge

Re: 440 "lunging" at low speed - 08/26/14 06:36 PM

Do you have a tach in the car? If os go drive it and give us the RPM it does the surging at, is the clutch out or in also

Posted By: larrymopar360

Re: 440 "lunging" at low speed - 08/26/14 06:45 PM

RapidRobert and PushButton have some good thoughts here. If you are on the gas still (although coasting doesn't sound like it but clarify please) I think PushButton has a good suggestion. I had some lunging or surging on one of my 360's that went away when I started running it w/o the vac advance connected.

If not on the gas, and in 4th or even 3rd, then it does sound like you may be in too high a gear.

Posted By: Challenger 1

Re: 440 "lunging" at low speed - 08/26/14 08:06 PM

Quote:

My 70 Plymouth 440 (4 speed) has been "lunging" when I coast at low speeds. It idles fine and runs out great through the gears. Only time I notice it is when I am 2,3, or 4th and just kinda coasting at low speeds.....440, Holley 750 Street Avenger,stock heads, Edelbrock Performer manifold and Hughes Whiplash cam. Can you guys give me some advice on what might be going on here and how to straighten it out? Thanx

440+750carb=lean.
My guess is a lean surge is what your experiencing. Just my guess. Jet it up some and see if I'm right. When you unplug the vacuum advance you are just applying a band aid and missing out on good cruise power and mileage.

Posted By: 70VERT

Re: 440 "lunging" at low speed - 08/26/14 08:59 PM

Basically, it's at low RPMs with very little throttle. For instance 2nd gear around 10mph, it'll surge up and down enough to clang the drive train. 3rd gear comparable only at a little higher speed.
I know enough when to downshift, thats not it.

Posted By: 69/70 Plymies

Re: 440 "lunging" at low speed - 08/27/14 05:29 AM

How long has the Whiplash cam been in the car and what's your rear gearing?

Posted By: 70VERT

Re: 440 "lunging" at low speed - 08/27/14 05:47 AM

Cam's been in for about a year and a half. 3:55 gears

Posted By: 69/70 Plymies

Re: 440 "lunging" at low speed - 08/27/14 06:25 AM

OK, if it's true you are not in too high of a gear, these are some areas to check (if apply to your car): low-speed or range circuits of the carb, incorrect low-speed calibration of the distributor, incorrect ignition timing, leaking vacuum advance diaphragm in the distributor, or blocked distributor vacuum passage(s)in the carb.

Posted By: Ply72rr

Re: 440 "lunging" at low speed - 08/27/14 06:29 AM

Quote:

Quote:

My 70 Plymouth 440 (4 speed) has been "lunging" when I coast at low speeds. It idles fine and runs out great through the gears. Only time I notice it is when I am 2,3, or 4th and just kinda coasting at low speeds.....440, Holley 750 Street Avenger,stock heads, Edelbrock Performer manifold and Hughes Whiplash cam. Can you guys give me some advice on what might be going on here and how to straighten it out? Thanx

440+750carb=lean.
My guess is a lean surge is what your experiencing. Just my guess. Jet it up some and see if I'm right. When you unplug the vacuum advance you are just applying a band aid and missing out on good cruise power and mileage.

Unplugging the vacuum advance to see if the surge goes away could be a good test, if it does stop the surge maybe an adjustment to the Vacuum advance with a allen wrench would take care of the problem. The instructions that came with my MP ignition kit mentioned a low speed surge could be caused by this.

Posted By: GTX MATT

Re: 440 "lunging" at low speed - 08/27/14 02:52 PM

You're at 1000 rpm or less at 10 mph in second gear, I think your problem IS that you need to downshift. Additionally this is not a stock engine, and doesn't pull as much vacuum at that speed. More initial timing might help it.

Posted By: JohnRR

Re: 440 "lunging" at low speed - 08/27/14 03:11 PM

Quote:

Basically, it's at low RPMs with very little throttle. For instance 2nd gear around 10mph, it'll surge up and down enough to clang the drive train. 3rd gear comparable only at a little higher speed.
I know enough when to downshift, thats not it.

Why are you in second gear at 10mph with 3.55's ???

Posted By: crazyjjk

Re: 440 "lunging" at low speed - 08/27/14 03:11 PM

Quote:

Quote:

My 70 Plymouth 440 (4 speed) has been "lunging" when I coast at low speeds. It idles fine and runs out great through the gears. Only time I notice it is when I am 2,3, or 4th and just kinda coasting at low speeds.....440, Holley 750 Street Avenger,stock heads, Edelbrock Performer manifold and Hughes Whiplash cam. Can you guys give me some advice on what might be going on here and how to straighten it out? Thanx

440+750carb=lean.
My guess is a lean surge is what your experiencing. Just my guess. Jet it up some and see if I'm right. When you unplug the vacuum advance you are just applying a band aid and missing out on good cruise power and mileage.

I would also be inclined to believe it is a lean surge.