351W hesitates on acceleration - thoughts?

When I'm driving and I step on the gas, there's a slight hesitation before it takes off. If the engine is cool (just beginning trip) and I don't give it enough gas, it will die on me--happened twice--. Once I've been driving it doesn't die but does hesitate momentarily EVERY time I press the accelerator.
Also, when I go to start when it's cold it fires right up without much effort at all. Once it’s been driven at all it doesn't want to start without pressing the accelerator to the floor. I’m not sure if this is somehow related to the hesitation problem, or not.

The carb (Autolite 2100) was rebuilt over the winter. Could there be a carb adjustment that is needed to correct both of these issues?

Thanks!  

When hot starting requires WOT, there is fuel being leaked into the intake, hot soaking, after the engine is shut off. Maybe float level too high.
But the hesitation sounds like the acc pump shot is lean or has some lost action in the linkage.  

Thanks for the feedback!

So even though it will be hard to start after it's been started, even if it's not hot, you still think it could be the float level too high?

It doesn't hesitate when revving parked, just under load? And even then it doesn't hesitate when it's punched hard. Does that still sound like the acc pump? And if so, any idea how likely it is that the new acc pump is shot?  

There are several issues that can cause that. As many cars have too much pump shot as have too little,,,so find the right adjustment that doesnt overwhelm the engine(everyone always thinks its too little). The first thing I would look at is timing. Make sure your running a good initial lke 8 to 14 degrees BTDC and make sure that both your centrifugal and vacuum advance are working. Retarded timing is one thing that will cause a hesitation. The engine requires advance to have a crisp throttle.
If those two arent your problem we can talk about the idle system which springboards you into the main system and must provide enough fuel in the transition to the main system. If you have a carb for a 289 on there its possible you may not have enough fuel in the idle system.  

Some excellent points, thanks!

I had the timing set at 6 BTDC as indicated in the manual. I advanced it to about 10 yesterday and it may  have improved just a little. Maybe I should try closer to 14...what do you think?

The car is all numbers matching (I verified this), so the Autolite 2100 is original.

I also checked both advances and they're working fine.

Lastly, is the adjustment for the Acc Pump just the three holes on the arm that runs to the Acc Pump (not really sure what it's called)? I left it where it was originally, in the middle one).

Thanks again!!!  

if the timing is retatded its "possible" to get some hesitation. as the harmonic balancer ages the outer ring with the timing marks can move a little and your timing marks are no longer an accurate way of setting the timing with a light. when i build an engine i find TDC and with the front pulley in place and mark TDC on the pulley cause it doesnt move. I use BHJ balancers but even the rings on them can rotate and these are the finest made and at $495.00 they better be !  

So you think I need to adjust my timing some more?  

Advanced timing helps you to get past a hesitation because it gives the engine a little more power.The correct timing for your engine is advanced as far as possible without pinging. If it pings back off a couple of degrees, then thats the best setting(whether its 16 or 10 btdc). Often you may have a slight carburetor flatspot and advancing your timing will help you to get past this. Of course ideally you'd like to fix the flat spot, but that can be difficult sometimes.  If you had the perfect (read closed loop fuel injection) air fuel ratio you probably wouldnt have the flatspot.  Try the accel pump in the other two holes and see if it makes a difference, but my guess is the middle one is good. Opening up your idle system a little bit may also help, the idle system flows fuel up to 30 miles an hour or more depending on load thru the transfer slots in your carb. A slightly bigger idle jet size may help but this requires specific drill sizes you dont have(and its a permanent change as it drill out an orifice) so lets not try that yet.  

Excellent! I'll try advancing the timing some more. I'll let you know how it goes.

Is the consensus on the tough time starting (when its been run recently at all) that the float level is probably too high? That's the one thing that I didn't get perfect in the rebuild. When I went to measure the depth of the fuel to set the float level (while the engine is running, as recommended), fuel started squirting out all over. I was not ok with that, so I hoped that the previous float setting was good. *fingers crossed*  

I advanced the timing to about 12. Seems a little better (ie it's not dying on me) but it still hesitates if I don't give descent throttle. Not sure if I should advance it any further or move on to some other culprit...  

did you check the point gap before setting the timing ? always check that first. i always set the point gap at .018  

I haven't checked the point gap since I first set it a few months ago (it ran fine at that point). Do you think I need to check that again? Do you think that's more likely to be the problem than an Acc Pump problem or adjustment?

The guy I bought the car from (the original owner) has marked in the book that the timing is best at 6 degrees BTDC, and the dwell is best at 21. This is why I selected these numbers...and they're each within the allowances set in the book.  

The best timing is where you ping a little and the engine comes right out of it. Generally speaking thats somewhere around 12-16 deg btdc. The dwell is set at 30 degrees, not 21 not .021 but with a machine that measures dwell angle which should be 30 degrees. The allowance set in the book is 28-32 degrees dwell. Most people are changing over to Pertronix but points are still reliable ,,,sorta.  

the .018" i was refering to was not with a dwell meter but with a feeler gauge and that was per a factory manual back in the 70's and i did at one time try everything from .016 to .022 and the best results seemed to be at .018 and i always set the timing by ear. at that time i could by AMMOCO super premium gas that was 102 octain ENCO (EXXON) was 98 octain and the rest was around 97 octain so detonation was not even thought about until you ran 12.5 or more compression. Do what Mechanicalguy48 recomends and set your timimg just at ping for max performance. I wanted the max power out of my stang cause i raced for MONEY ! and still race for money ! roadrace now that is , car doesnt launch very well with 3.00 gears in the back !  

My bad...I meant to say that I set it to .021 with a feeler gauge.

I'll try advancing it a little further. Do I need to reset my points after that?

If I am still having problems do you think it would be the Acc Pump?

Thanks again guys!