70 roadrunner surges and hesitation

[BL1 70 RR]

Hey guys, when I accelerate my car it sounds and feels like it is bogging down, when I finally get it up to speed the car surges and hesitates when I'm crusing down the road. I replaced the fuel pump and re tuned the carb so I'm pretty sure that those aren't the problem. Could this be a timing issue? The car has a 383 with a cam in it and an edlebrock 1406 carb. Thanks for any help!

 

[Lionized]

I have the same carb on my 383. Check the accelerator pump linkage and be sure that it is located in the uppermost hole.
Get back with your results.

 

[Auggie56]

Have you just made a change in something, that was followed by the stated symptoms ? That surging sounds like a lean condition, caused by a vacuum leak. Which could cause a stumble on acceleration. Look for a vacuum hose off or damaged, loose carburetor fasteners or loose intake bolts. If you have power brakes, the booster could even leak vacuum.

 

[BL1 70 RR]

The only change I've made was when I changed it to the top accelerator hole in the linkage. It was originally in the middle hole, however when it was in the middle hole it would have rough idle and when I changed it to the top hole in the linkage it idled much smoother. It drove pretty well in the top whole for about 40 miles before these problems began.

 

[moparedtn]

The accelerator pump should have no effect on idle quality.
That alone tells me you've got issues with the tuning/jetting of the carb or even other issues.

 

[Lionized]

The only change I've made was when I changed it to the top accelerator hole in the linkage. It was originally in the middle hole, however when it was in the middle hole it would have rough idle and when I changed it to the top hole in the linkage it idled much smoother. It drove pretty well in the top whole for about 40 miles before these problems began.

Have you checked the float levels? (7/16")

 

[crash89]

I had the problem you describe about two weeks ago. Mine was the coil.

 

[BL1 70 RR]

I'll check the float bowls and get back to you guys, how would I know if the coil is bad?

 

[crash89]

I'll check the float bowls and get back to you guys, how would I know if the coil is bad?

How I tested my coil was by pulling the plug from #1 cylinder (you can pull any plug though), cranked the motor with the plug grounded against the head, and looked at the spark while my son cranked the engine. My spark was weak and orange. It should have been strong and blue. I swapped the coil out and it had a blue spark. I also tested the ohms on the old coil after doing that and they were out of spec (I forget by how much). I hope this helps.

 

[BL1 70 RR]

I checked out the float level and that's good. Thanks crash89, I'll check that out! From the apperance the coil looks to be the original one so it might be going out.

 

[BL1 70 RR]

I tested the coil and it was sparking orange ones, I'm going to replace it and hopefully that will solve the issue! Thanks for the help!

 

[wsutard]

BL1, any update here? I have the same issue.

 

[BL1 70 RR]

No unfortunately it is still surging and has hesitation, regardless my coil did need to be replaced. It was shooting weak orange sparks so I replaced it.

 

[miller]

Something else to think about. What do you have for a fuel filter, and last time it was replaced. And (forbid), filter on your fuel sending unit? Could sound like a fuel delivery problem.

 

[wsutard]

I have my car in the shop right now for this issue. They are going to run through the timing, ignition and carb to see if they can figure out what is going on. Will let you know what they end up finding/fixing.

 

[BL1 70 RR]

I don't think it could be a fuel issue because I replaced the fuel tank and sending unit last year then I replaced the fuel pump and both filters last month, I'll check those out again and see if they are the problem.
Thanks Wsutard, keep me informed!

 

[Lionized]

I don't think it could be a fuel issue because I replaced the fuel tank and sending unit last year then I replaced the fuel pump and both filters last month, I'll check those out again and see if they are the problem.
Thanks Wsutard, keep me informed!

Have you put a timing light on yours? If so, what are you set at? Points or electronic? If electronic, which control unit are you running?

 

[wsutard]

Got word back from the shop about my bucking/hesitation. They checked the timing, ignition, and carb. No issues. The engine vacuum is weak and the compression is 110 when it should be 155. Their engine guru thinks it's either a bad valve adjustment or the previous engine builder didn't put the Keith Black pistons together correctly. Supposedly they are known to have a specific installation process average builders aren't aware of.

They are going to re adjust the valves tomorrow morning.

If its the pistons then I'm not sure what I will do.

 

[BL1 70 RR]

Did you car drive normally and then begin to surge or was it always surging?
Mine had its engine rebuilt 200 miles before I bought it and mine drove well for the next 2000ish then it started to surge.

 

[wsutard]

I just bought it about a week ago. Engine was rebuilt two years ago. Not many miles on it.