...operating throttle from under the hood

I just got my newly built 318 running. Its basically stock, albeit upgraded; Carter AVS from a '71 383 on a 273 castiron manifold, Comp's 340/360 cam and springs exhausting through magnum iron manifolds and duals out the rear.

I need to do some tweeking to eliminate some hesitation, but by manually working the throttle I can get it to run up through WOT pretty smoothly. However, sitting in the car, working the gas pedal, Its as if I'm running a different car. run up is erratic and WOT sounds like its dropping a third of the cylinders.

Help! What gives?? Its moving the same linkage!!

grab a helper & have him work the pedal with you under the hood to see what is different between the two operations.

Is the air cleaner off(or on) both ways?? If it is off when you are working the throttle by hand and on when operating it by the pedal it could be an airflow problem caused by the aircleaner..

I can`t see a cable having anything to do with the running erratic part unless the cable was sticking. Maybe you have a exhaust leak at the manifolds, carb issues or something that is making it sound funny. If you were saying it wasn`t opening all the way up or something like that then I would say adjust the cable or maybe you have the wrong cable or brackets.

If gas pedal is the same as my e body, it mounts on a pivot like a teeter totter. If your right foot contacts the bottom of the pedal only, you may see different results than if your foot is above the pivot point.

At one time I would very occasionally have the pedal stick to the floor on my 512 six pack(yes quite a thrill). Investigated linkage throughly, posted problem on forums,,,including this one to no success.

Could not get it to stick with engine not running,etc.etc

Then one day had my head under steering column to throughly check out the pedal assembly and found the cause.

If I would push pedal down by hand normally, it would return upon release.

However if I pushed down near the bottom of the pedal, causing it to 'pivot' down, the bottom of the pedal would barely catch on a ridge of decorative rubber built into the heel pad under the pedal, causing it not to release and return when I let up on the gas.

2 minutes with a Dremel grinder wheel and all is well.

Make certain that you are not merely 'toeing' the bottom of your pedal. Unlikely cause of your problem, but possible. I happen to be a 'toer' when driving and have at times found my toe slipping off the bottom of the pedal on my wife's suv.

Go Big Red,,,,born and raised in Lincoln. Spent many a weekend at the old Air Force base drag strip in Omaha back in the 60's in my misspent youth.

Just for fun check and see if the pedal linkage is hitting the ignition wires under the dash in the harness.

Along stummpys thought, is the engine grounded to the battery and body? Could it be that the throttle cable is acting like the engine to body ground? That could cause ignition break up as the cable moves and makes/breaks contact.

This is what I would look at

Well, (sheepish grin, here) I don't know why, but the stock braided ground was not connected to the bulkhead. I know I bolted it up at some point but did move some things around to mount the hei affair. Must overlooked re attaching it.
Unfortunately, it didn't cure the issue. Already read y'alls next thought. Check braid's continuity. Ran out of daylight...

Scott

Also along the lines of with and without Air cleaner, are you sure your linkage isnt contacting the bottom of your air cleaner? I had a problem going smoothly to wide open throttle. Everytime I checked the linkage I had the air cleaner off. Finally had a helper do it while I was underhood with cleaner on and saw it happen. Fixed with a spacer. Long shot but that my 2cents

roe

Is the carb moving on the intake? when you rev it up by hand, your moving the throttle on the carb. when you rev it up by the pedal, your moving the throttle by a cable pulling back. Slightly loose carb base bolts (bottomed out maybe?) might work OK, but the cable pulling back might be creating a minor vacuum leak at the carb base.

The only other thing I can see would be the throttle cable or linkage inside the car, or under the hood, is moving wires that are loosing connection someplace.
We had a throttle cable one time that was a little frayed at the end. It caused all kinds of strange things before we finally just replaced it, and all the problems went away. Once removed, you could feel the cable bind up at some spots. Gene

extremely worn out throttle shaft holes in base plate ?