4 speed driving issues

[Polara_500_Jr]

Mornin all.

I'm not sure where to start, so let's hope someone here can get me pointed the right direction.

383/4 bbl. 4 speed. New clutch, new a833, new driveshaft, new AVS2 800 carb. 383 with fresh rebuilt heads. maybe 500-1000 miles on it since the work was done.

Accelerating is smooth and feels right. if in 1/2/3 and just holding steady speed in town, it gets jerky. not severe, just enough I feel it in the pedals and wheel, I do not think the wife noticed until I called it out. If you hit the gas pedal and accelerate a bit it smooths out.

I am not sure if this lies in the ignition? Carb? clutch?

@HWYCRZR been thinking about calling you and having you take it for a drive... but not sure how much you know with the manual trans..

 

[57fury440]

What gears do you have in the rear? At what RPM in each gear is it "jerky"?

 

[Polara_500_Jr]

3.23 gear.
I'll notice it 2k-3k?

 

[CBODY67]

It seems that in manual transmission vehicles, sometimes there are harmonics which happen at certain rpms and such, which can cause some jerkiness. Normally, it's like you are coasting and hit a road speed that the engine doesn't like, so it resists being pulled down that much in that particular gear, so the cure is to disengage the clutch and do a downshift so the road speed and gearing is better matched for the engine rpm. When this happens in 1st, then you disengage the clutch and stop or accelerate.

How long has this been going on?

In some manual transmissions, the issue of "gear rattle" can happen at idle speed in neutral. In some OEMs, they might add a damper or such, to help smooth things out. Or maybe use 80W-90 gear lube rather than something lighter, like atf.

On the engine side of things, I doubt it's an ignition-related issue at a particular rpm level. It could be an rpm where a slight lean calibration might cause what you mention. Being a manual transmission rather than an automatic, it's more noticeable with the solid coupling the automatic trans does not have.

What you might try . . . is to decrease the base timing about 2 degrees and see if it gets better and advance it 2 degrees to see if it gets worse. Which can be an easy way of varying the effective fuel calibration slightly for testing, without messing with the carb internals.

One side issue, to me, might be the spark plugs. How recent are they? Gapped to specs? Electronic ignition or points? Not that anything's wrong enough to cause a misfire, but possibly not getting things ignited "all the way" enough?

In that thought, you might try some NGK V-Power plugs, which put the sparks at the edge of the ground electrode for a better ignite situation. Or their fine-wire Iridium plugs, which allow an unrestricted ignite, for better combustion. The V-Power plugs have all of the design and construction tricks, in the electrode configuration, for a normal spark plug. They were also used by Toyota OEM for their ability to burn leaner mixtures, which I can verify as I like to set my automatic chokes as lean as possible, to get the choke open as soon as possible after a cold start in the morning.

It might just need some tweaking of various things. What I mentioned will not cost too much money to do, just time, and they can be can be un-done easily if they don't work.

Please keep us posted on your progress and findings,
CBODY67

 

[Polara_500_Jr]

It seems that in manual transmission vehicles, sometimes there are harmonics which happen at certain rpms and such, which can cause some jerkiness. Normally, it's like you are coasting and hit a road speed that the engine doesn't like, so it resists being pulled down that much in that particular gear, so the cure is to disengage the clutch and do a downshift so the road speed and gearing is better matched for the engine rpm. When this happens in 1st, then you disengage the clutch and stop or accelerate.

How long has this been going on?

In some manual transmissions, the issue of "gear rattle" can happen at idle speed in neutral. In some OEMs, they might add a damper or such, to help smooth things out. Or maybe use 80W-90 gear lube rather than something lighter, like atf.

On the engine side of things, I doubt it's an ignition-related issue at a particular rpm level. It could be an rpm where a slight lean calibration might cause what you mention. Being a manual transmission rather than an automatic, it's more noticeable with the solid coupling the automatic trans does not have.

What you might try . . . is to decrease the base timing about 2 degrees and see if it gets better and advance it 2 degrees to see if it gets worse. Which can be an easy way of varying the effective fuel calibration slightly for testing, without messing with the carb internals.

One side issue, to me, might be the spark plugs. How recent are they? Gapped to specs? Electronic ignition or points? Not that anything's wrong enough to cause a misfire, but possibly not getting things ignited "all the way" enough?

In that thought, you might try some NGK V-Power plugs, which put the sparks at the edge of the ground electrode for a better ignite situation. Or their fine-wire Iridium plugs, which allow an unrestricted ignite, for better combustion. The V-Power plugs have all of the design and construction tricks, in the electrode configuration, for a normal spark plug. They were also used by Toyota OEM for their ability to burn leaner mixtures, which I can verify as I like to set my automatic chokes as lean as possible, to get the choke open as soon as possible after a cold start in the morning.

It might just need some tweaking of various things. What I mentioned will not cost too much money to do, just time, and they can be can be un-done easily if they don't work.

Please keep us posted on your progress and findings,
CBODY67

It's points, fresh rebuild by @halifaxhops so I am confident that is fine.
it has 75-140 synth gear lube in it.
plugs are 500ish miles. I should pull them and see how they look.
It's been there all along, but I think it maybe got a little worse with the carb tuning we did. adjusting the timing a few degrees may let me track it down quick. Hopefully I can find the time this weekend to do all this

 

[HWYCRZR]

The ignition was pretty clean at idle when we put the scope on it. Each cylinder was even and had a clean pattern. What we didn’t try was the scope at a higher rpm to see if it changed at all. We also didn’t check the vacuum advance at a higher rpm.

I could give it a drive. I grew up with manual transmission trucks. With a manual transmission you don’t really coast so if you are lugging the engine a bit it will be a little jerky.
Also if your throttle pedal spring is a little light it could be a little sensitive.
I should be around tomorrow afternoon or evening (Friday )then Sunday. Just doing some patio work to prep for a garage addition.

 

[66 Monaco 500 365]

Sounds like lean surge to me.
My $.02

 

[fury fan]

An 800 is a pretty big carb for a 383 unless it's been modified enough to need it.
In which case, at 2k rpm it might not be happy to be in a large car.
3k rpm should be awake enough to not have any jerking, though.

 

[LocuMob]

An 800 is a pretty big carb for a 383 unless it's been modified enough to need it.
In which case, at 2k rpm it might not be happy to be in a large car.
3k rpm should be awake enough to not have any jerking, though.

It might be a little big, but the carb will only use what it needs. I use a 750 on most everything I have, with an 800 avs 2 ready to go on a 413. I stopped using 600's when my last one was stolen over 20 years ago.

 

[Polara_500_Jr]

I haven't had a chance to even tear into it yet.....

Work travel, and more work travel. Oh, and drive 952 miles in a day to buy a clothes dryer, and a 65 polara, then stop and tour LocuMob's stash of cars!

952 miles, 22 hours. Not sure I am caught up on sleep yet.

 

[WissaMan]

I'd lean towards the carb tuning or a vacuum leak. Would you say that your pedal position is just barely cracked? Maybe it's oscillating between transition points (not sure if I'm saying that right).

I could also be full of poop. Just trying to throw some ideas out there.

 

[fury fan]

I'd lean towards the carb tuning or a vacuum leak. Would you say that your pedal position is just barely cracked? Maybe it's oscillating between transition points (not sure if I'm saying that right).

I could also be full of poop. Just trying to throw some ideas out there.

That's what I was thinking about hte carb being too big, if it's on the edge of the off-idle transition slots (due to some mis-tuning?) it might make some surging that you wouldn't feel with an AT because the torque converter absorbs it. With a MT, that cushion is missing. (@LocuMob - that's why I mentioned the carb size)

 

[Cartel]

sounds like a part throttle issue like its dripping down the carb or leaning out. maybe a couple taps on the float bowl and some seafoam in the tank? was it sitting up a bit?
I know a loose timing chain would act like that too because the timing is see-sawing at the near constant