I don't quite know how to explain it clearly without taking you for a ride in my car -- but -- when I hit between 35-40 MPH and keep it steady there, my car is "jerky". I don't know if I'd call it a hesitation, but is almost feels like it wants to shift into another gear (it's automatic).

If I ease up on the gas pedal, it's fine, and if I give it gas and go faster, it's fine right away, then gets herky-jerky again.

The engine, carb and tranny are all newly rebuilt, if that matters.

Any clue what could be causing this, or is it just a symptom of being 40 years old and it's a normal reaction?

 

It sounds like the balancer and tranny are not quite on the same sheet of music. I would take it to a C4 mechanic and tell them what is happening. It sounds like it just doesn't have enough RPM to shift, but just enough to tell the balancer it's just about time to shift. At any rate, you need to get that tranny looked at. Or, learn to drive it as it is by watching your speed when it wants to shift, then give it a bit more gas.

 

You've done an excellent job of explaining a light load, lean run condition.

It could also be a vacuum hose left off, and the idle mixture was compensated for it. So it only affects off idle, light load conditions.
So if it is not the transmission, or a vacuum leak, my guess would be your old carb has seen better days. Even from the factory these 6 cylinders had issues with stumbles and hesitations. Usually it included stumbles on initial take off too.
From your description, it sounds like the vaporizer passages inside the aluminum carburetor body are getting corroded, and are plugging up. If this is the case then it is time for a new carburetor.
You may be able to advance the timing to reduce this issue, but it will come back as the corrosion continues to grow.

Something to consider, is adapting a 2 barrel carburetor. This is pretty involved, and can take upwards of 4 to 6 hours depending on whether or not you buy a kit (Clifford Performance, Fordsix performance, etc). I've done a few of these conversions, utilizing either an Autolite, Holley, and also did one with a Webber. I have never used a kit though. They didn't have "kits" like that when I was was doing this. Made a world of difference in performance, and drivability.

Hope it's something simple for you. Good luck,

 

Carb was just rebuilt (as was engine and tranny) so I hope to heck it's in awesome shape.

Every so often the car (when not doing this herky jerky show) feels like it wants to shift but it takes extra time. I liken it to my Toyota pickup truck in cold weather going uphill -- automatic also -- you can feel it wanting to shift but it takes an extra minute or two to actually do it.

 

It's not the carb.

Long story -- called the body shop and he told me to bring it over right away. I took him for a ride and at first he could not detect anything, then said it was a "skip" but was shifting fine. We go back and he got under the hood and tinkered for a bit. He said he smelled fuel and wasn't sure why. He had me start it up and tinkered some more, then said "come hear this" and when he pushed down on the plug wire, it would make a snapping noise.

The problem, he says (and he's an old Ford guy) is I have a bad plug wire, and what's happening (he patiently explained this to me) is the spark isn't grounded and the fuel in one chamber (cylinder??) isn't coming out (hence the smell).

He said he could order new wires but would have to get a price, which I figured meant big bucks. He came back and had a look on his face that scared me, said "I have the price" and then tells me $82 installed. Duh? I was thinking hundreds the way he had to check the price! He also asked if I wanted original wires and I asked what he recommended. He said what I have are originals and look how they are ... and he said he would order new ones "that are good and not Motorcraft".

He seems to know his stuff so I'm going to believe him that this is nothing more than the restoration guys installing a set of bad wires and not checking carefully enough to detect that.

 

Also, replace the cap, set the points (if it still has em), get new plugs, and if the fuel filter wasnt in the carb, replace that too.
-P.

 

And, what did he say was wrong with original Motorcraft wires? Ford engineers seemed to have liked them, and used them for eons without fail. Sounds to me like he is getting some kickback from some company for pushing their product. Do you actually believe all that these guys tell you?
http://www.motorcraft.com/products.do?item=14

 

Uh, don't shoot the messenger? I'm only repeating what I was told to confirm it here. But yes, I do believe him. I see the "original Ford" wires that I apparently bought that are bad and after restoring hundreds of cars, if he feels I should get what he recommends, then I'll go for it.

By the same token, we here all love Mustangs, right? But how many people do you talk to that tell you any Ford is a piece of crap and Mustangs are all garbage? Chevy people swear by Chevy, Ford people swear by Ford, etc.

Do you have certain brands you prefer over others? I'm sure there are people who will tell you you're crazy to choose the brand you prefer.

It's misfiring with brand new wires, that's the bottom line.

 

It has new points and plugs and he checked the fuel filter and said it was fine.

What "cap" needs to be replaced? Distributor cap?

 

That is great news! maybe not quite as good as a vacuum line unplugged, but almost[sm=smiley20.gif].

From everything you've posted, it seems you have found a good shop. I like to hear that he takes the time and explains things. Your interpretation of his explanations makes me feel comfortable that he is treating you right.
Congratulations, as hard as it is for me to admit this, there are still places that take advantage of people.
Great to hear about the good guys!

Sometimes a note of comendation to the B.A.R. (Beaureau (sp?)of Automotive Repair), and/or the local chamber of comerce/bbb (if he subscribes) goes a long way. Seems these groups always hear the horror stories, but rarely the good stuff.

You know, the plug wires may not have started arcing until you got a couple of miles on it. Sometimes, that kind of stuff happens. You start putting it under the daily stress, that no shop has time to do, and the little things will show up.
Nice thing is, as you get this stuff out of the way, you'll get more and more confidence in both your car, and your own knowledge.

I spent a little over $1,000.00 on belts, hoses, tune up stuff, filters, etc (just the parts!), and one weekend going over everything, when I picked up my car. Took off the next weekend for a 300 mile drive, feeling confident enough to ask my G.F. if she wanted to go along. We had a wonderful day.

Good luck and have fun!

Scott