My 67 CS (330) 4 speed (3.90 rear) has a lungeing problem at low steady speeds ( up to 30 mph, or below 2,000 rmp in any gear). It will jerk back and forward when using little or no throttle while cruising, and very definitely coming to a stop in 4th below 1500 rpm. I have to throw into neutral below 1800 to make sure it it smoothe. Cruising in neighborhood at 20 mph feels like a stop and go bumper car.
Engine rus smooth if you are accelerating (slow or WOT) or at steady speed over 45mph. There is a whine in either tranny or diff below 2500 rpm, and will slowly fade as speed increases. I can live with the whine, but the bucking is getting to be a PITA!
Engine never misses... ( HEI and new Holley 600), plugs gapped @ 045.
no other issues. Universals seem tight without play. Suspension is almost new. Car has always had this problem since I have owned it.

Any suggestions as to where to look in the drive line?

Many thanks
Hotrodder

 

I had one car do this that was running a tad lean due to a small vacuum leak, and another time with a stuck open ERG valve (lean again). It happened in the mornings when under 40*when it needed all the fuel it could get and EGR is disabled. Fixing the problems cured it both times.

I have heard that broke springs in the clutch can do this also, more repeatedly than my issues above. Can anyone else verify this?

 

I'm calling carb issue on this one. Like the too lean situation. I remember as a kid driving a stick and you when the car starts to lurch and lunge and you have to put in the clutch or give it gas? it's because it is running lean, IMO. There is def not enough gas reaching the engine. My current ride does this sometimes as well. I just push in the clutch, give it a rev and restart.

 

Some times too much timing will cause a lurching that you may not feel with a automatic but definitely will with a stick. Rev your car up to the rpm you feel it at in neutral and if you see the engine rocking some on the mounts that maybe it.

 

Recently I dialed in the MSD billet on my Cutlass and had way too much timing in it. It caused the car to do exactly as you described. I took the timing out and it ran as smooth as silk. Something to check.

 

Since the carb is new ( the edelbrock was not running on the idle circuit!) I'll recheck the timing and even set it back to see what happens. My last carb was running very rich so I don't think that it was a lean run problem.
I'll let you all know.

 

Gentlemen,

Here is the update.
'67 CS conv.
Engine stat: 330, iron heads, stock exhaust manifold,
Edelbrock rpm performer intake, \Holley 600 / HEI

Had brought it into shop for vacuum leak _ 5 - 6 " @ idle Carter competition ( edelbrock style) 625 -carb runing rich. Probably has a cam in it, but I don't know if true... have not dis-assembled engine to determine.

No leaks found-- replaced intake gaskets, added heat crossover runner blocks, new Holly 600 added,
Shop timed to 40 degrees advanced at idle!. ( no ping, no hesitation,cranks easy)

Today,
Vacuum @ idle = 13 "
idle rpm = 700
reduced timing @ idle to 33 advanced ( vac. disconnected)
centrifical advance - 33 at idle,

Timing to 42 degrees @ 2000 rpm (did not change weight curve)
60 ( sixty) degrees at 2000 rpm with vac. advance.
Vacuum @ 16 " at 2,000 rpm

Runs smooth, 90% of rubber- banding eliminated at 1000-15000 rpm
runs 180, all day, even in hot traffic .. May go to 200 @ highway ( 75 mph)
no ping. no hesitation, no bucking on low speed WOT.

I believe the shop timed it by advanced until it was hard to crank, then retard 2-3 degrees.

RUNS FINE!!! NO PING, no hesitation, limited lungeing.

Thanks for the timing tips.
Any other comments/
Hotrodder

 

SAY WHAT?

 

I saw that , too.