Buck and Surging Problem Under Load

[Road Grabber]

I have this ongoing issue with my 383 4 barrel. I have recently replaced the carb with a fully restored carb that was correct just because I was going to do that anyway. The engine runs fine while revving the engine in the engine compartment. No back firing or hesitation.

When I drive the car it spits at times at acceleration and feels like it's surging and bucking. Only under load does it do this. It does not have a flat spot in neutral. Last year it felt like it was fuel starvation. It almost stalled when cornering. I thought the old carb floats were not adjusted right. I put the car away for the winter and was sent out a for carb restoration until spring. This year engine seemed to run great with the new carb. Idles great. Revving the engine under the hood there is no popping and the secondary circuit works fine.

When I test ride it the car it bucks and pops when you step on the peddle to accelerate. I did add high test (no alcohol always used) to the existing fuel. The old fuel had the additive for storage. I have been tracking this down for some time. I changed the points and cap (dual distributor) and even added a spacer between the carb and a vent line to the fuel line system to prevent percolation.

My next guess is maybe new ignition wires. Any thoughts would be greatly appreciated!

It's annoying driving the car. It doesn't have a smooth acceleration when you speed up.

Thank you in advance!

 

[RGAZ]

I would check the base timing and the timing advance first. Still points?

Then tell us what you find before replacing stuff.

RGAZ

 

[Darter6]

How old is the coil ? Had that problem on a 68 Coronet. Idled fine,rev fine, would buck and spit under load.
Changed the coil and all was good. Just a thought.

 

[hemi446]

Just the points and not the condenser ? And does it seem to be on the same one or two cylinders ? Pull all the plugs and look at them, also check for vacuum leaks around the intake manifold and under the carb.

 

[LowBikeMike]

Sounds like a secondary engine miss. What does it do it you put it in gear, foot on brake and lightly accelerate? Inspect the plug wires for burns, carbon tracking at the plugs, etc.

 

[Road Grabber]

Thank you for all the suggestions. I have thought about a coil, wires.....

I did change the condensers. All new stuff under the cap and timed it.

I know it's not the carb(s). I have used two or three carbs and the same problem. I thought at first it was fuel starving with jet or bowl level problems because it wanted to stall on a corner. It did run well before so it's something that has developed.

It's always temperamental when restarting the engine after it sat so I was thinking percolation. I installed a carb spacer with the additional gas vent line since I had the right sender to use one. That hasn't been a problem now with the holley carb.

Sounds like a secondary engine miss. What does it do it you put it in gear, foot on brake and lightly accelerate? Inspect the plug wires for burns, carbon tracking at the plugs, etc.

It's a four speed. Tough to do that but good suggestion. It coughs like an accelerator pump problem. Once it catches up it bucks in the seat of your pants and feels like it being held back.

It's definitely a problem while under load. I will check the wires for ohms and watch the engine run at night under the hood to see if there is any light shows sparking to the head. I will also look into a coil.

I was thinking about getting one of those "all in one" distributors that have everything and take the distributor with points out.

It feels like a fuel starvation problem but it's not in my opinion. The engine wants to go but it being held back.

Thanks again for the input!

 

[RGAZ]

Just the points and not the condenser ? And does it seem to be on the same one or two cylinders ? Pull all the plugs and look at them, also check for vacuum leaks around the intake manifold and under the carb.

This is good advice. Did you have to adjust the idle a lot when you put the new carb on? I would expect the idle to be crappy or high if a big vaccum leak, but use the "carb cleaner mist" technique to see if there is a vacuum issue.

My question was: Do you still have the stock ignition installed (points)? If so check them AND the timing advance. Maybe you have a bad dashpot on the dist and not getting appropriate advance under load. On second thought...did you connect the vacuum advance to the correct port on the carb? Maybe a leak on the dashpot.

RGAZ

 

[Road Grabber]

This is good advice. Did you have to adjust the idle a lot when you put the new carb on? I would expect the idle to be crappy or high if a big vaccum leak, but use the "carb cleaner mist" technique to see if there is a vacuum issue.

My question was: Do you still have the stock ignition installed (points)? If so check them AND the timing advance. Maybe you have a bad dashpot on the dist and not getting appropriate advance under load. On second thought...did you connect the vacuum advance to the correct port on the carb? Maybe a leak on the dashpot.

RGAZ

Good suggestions
I do have stock ignition prestolite points.
Are you saying watch with a timing light to watch advance?

There are two I believe port locations. Any idea which is correct? I know I didn't use the one at the back side....

 

[Johnpat]

Coil

 

[Road Grabber]

I will definitely be looking into a coil. Thank you

 

[HALIFAXHOPS]

You said you changed the points and condeser with "new" New parts store?

 

[Road Grabber]

Yes new parts.

 

[HALIFAXHOPS]

Possibly be a bad New condenser, they fail alot! Any chance you have a ounce spring scale to measure the point arm tension? Should be 17-22

 

[RGAZ]

Good suggestions
I do have stock ignition prestolite points.
Are you saying watch with a timing light to watch advance?

There are two I believe port locations. Any idea which is correct? I know I didn't use the one at the back side....

Yes, use timing light to verify advance with RPM.

I am not sure of the exact port you should use, but it should be the one closer to the baseplate for below throttle vacuum I believe.

If advance is working and no vacuum plate, then I would go for condensor and coil.

RGAZ

 

[Road Grabber]

So I can update what I have been checking and discovered....If I didn't get to your advisements please know I appreciate it and plan to keep things going.

I have a steady just under 15" manifold vacuum.
I tightened up the manifold bolts a bit.
I discovered that a rubber plug that capped off the manifold fitting was cracked and replaced it.
I replaced the plug on the brake booster as well.

This improved the performance and left a flat spot.
I advanced the timing a bit which helped but still left a flat spot.
I was planning to get a step up accelerator pump nozzle.
Checked the accelerator pump lever gap and adjusted it.
Still a flat spot.

 

[RGAZ]

So now its just a flat spot? What RPM range or when you are doing what?

A roll into throttle is fine all strong?

Wire your choke plate open just to eliminate that possibility of tension setting incorrect.

RGAZ

 

[Road Grabber]

So now its just a flat spot? What RPM range or when you are doing what?

A roll into throttle is fine all strong?

Wire your choke plate open just to eliminate that possibility of tension setting incorrect.

RGAZ

Yes. Rolling into opening the throttle is strong. The air cleaner is off and the choke is wide open.

Just when I give it a quick throttle which is like you would when stepping off idle to let out the clutch or give it a sudden shot to pass get on it. You feel a flat spot and then it picks up. The engine idles smooth otherwise.

I can pull wires to see if there is a bad wire. It's been a while since I got shocked.....I have an accelerator pump nozzle ordered one step up to try it out.

I will be pulling off the cap soon and inspect the points again and check the dwell. Seems like a lot of little things adding up.

 

[Slap Stick]

Does it so it with the air cleaner/filter in place? Better or worse with filter installed?

 

[RGAZ]

Yes. Rolling into opening the throttle is strong. The air cleaner is off and the choke is wide open.

Just when I give it a quick throttle which is like you would when stepping off idle to let out the clutch or give it a sudden shot to pass get on it. You feel a flat spot and then it picks up. The engine idles smooth otherwise.

I can pull wires to see if there is a bad wire. It's been a while since I got shocked.....I have an accelerator pump nozzle ordered one step up to try it out.

I will be pulling off the cap soon and inspect the points again and check the dwell. Seems like a lot of little things adding up.

Good info, now we are getting into details.

Definitely go after accelerator pump/nozzle, that would be my next check (could be too big, could be clogged). I do not think its a wire but could be something in the advance, check the points and dwell just to be sure they are right and eliminate them.

This really sounds like a loose choke plate, the vacuum pulls it down but it opens back up. Did you wire it open? Like take wire and force it to stay open, I know I sound like a Dad, but sometimes you gotta repeat yourself. LOL

RGAZ

 

[Tman100]

Sounds like it is leaning out due to not enough of a squirt of the accelerator pump. If you have an adjustment for more of a squirt try that. I had this problem on my carb a few years ago. Once adjusted correctly problem went away