GT390 Hesitation... - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

69torino-t · 07-06-2008, 20:16

Hi folks, OK, I have the 69 Talladega running. Even the choke works. New radiator fit like a glove. Idles nice. Now the bad news. At part throttle there is a hesitation or balking when given her gas. If I ease off the gas she sounds good. The carb is as near as I can tell is the Autolite 4300. I had my Fathers friend look at it and he cleaned it up and replaced gaskets etc. and the accelerator pump is new. I have a high volume fuel pump. The fuel tank was fixed up by TankRenu. I had problems with a plugged fuel system a while back. My plan is to replace the fuel filter at the carb and I am seriously thinking of adding one in line to prefilter the gas. I will also replace the air filter as it's old and a lot of junk came off it when I shook it. I have spent a fair sum getting her going. The radiator set me back about $510. To change out the fuel line from tank to pump is about $100 to go stainless. The car has a Mustang motor (S code) in case anyone wonders why the Autolite carb is on there. I still have a stuck distributor in the block. It is running OK at least at low speed or idle. I am open to any suggestions. Maybe I missed something? Thanks, Dave

kdtrucker · 07-08-2008, 13:53

Why are you using a high volume fuel pump?? It's not really neccessary, I run a stock fuel pum with my 428 and it has 2 fours.
Use clear filters inline the fuel line,...you may have a bunch of debries in the tank.
As far as your carberator goes....call Pony Carberators in Las Cruces, NM. He'll tell you everything you want to know about the 4300.
575-526-4949

69torino-t · 07-10-2008, 19:43

Hi kdtrucker, I did replace the fuel filter and did add one (a clear one). Getting plenty of fuel. No debris, rust dirt or anything in the filter so far. Put a new air filter in and that seemed to help a bit. I also thought the advance might be rusty so shot some lube down there to loosen it up. I had problems on my old LTD II with sticky advance mechanism. At this point it runs sometimes real well and other times the hesitation returns. That's the real mystery. I agree the carb is the most likely cause. Oh, the fuel pump. Thought it was a good idea at the time. Guess maybe not in hind sight. My plan is to freshen up a Holley 4160 with gear driven secondaries. I want to figure this thing out. I am hoping that will solve this problem. I will consider sending the carb out to Pony Carburetion once I really know what's going on. Dave

kdtrucker · 07-10-2008, 23:37

you might want to check the dist. cap for cracks or build up. also check the wires and the plugs, it may be just that simple.....

69torino-t · 07-12-2008, 15:38

Hi kdtrucker, Thanks for the advice. I will put a new distributor cap and rotor in. I have a set ready to go. Just need to find a few minutes and git r done. Dave

69torino-t · 08-14-2008, 20:53

Hi folks, Just to let everyone know I solved the problem. Went through another carb, a Holley 4160 with center hung bowls and gear driven secondaries. After tuning up the carb, guess what? Same problem. So, after a little thought it occurred to me that the condenser might be the culprit. I swapped it out and that was it!

Took it out for a drive and it just got better and better. That thing goes. Don't even miss having a passing gear kick down. Just don't need it. Smokes the tires!

kdtrucker · 08-15-2008, 08:21

Glad you found your problem. isn't it always the little inexpensive thing that causes you to think the worst.

WerbyFord · 08-20-2008, 09:09

Great to hear it's solved!
The 4300 can be a fussy carb, they don't like dirt and the accel pump is very picky too so that was my guess as well.

If you had to ditch the kickdown on going to the Holley, check your auto shift points, they might be as much as 1000rpm lower now, unless you hold it in gear like I used to do.

If you like that Holley, you could either change throttle shafts or maybe adapt a "rat trap" throttle mechanism from an older big Ford 390 to work, then run the kickdown from the rat trap down to the trans. Most intakes have the two holes near the back to mount the rat trap assy.

BTW, as I gather it, you might officially have a 390 IP or "Improved Performance", not a 390gt. For 1969, the 390gt changed from a 600cfm Holley to the 600cfm Autolite 4300 and got a milder cam, to avoid needing a Thermactor pump perhaps.

Usually on an engine with stock iron exhaust and mufflers, I can get the Auto 4300 to cut times as good as a 600 Holley after a lot of fiddling, but a given engine might "like" a given year of Auto 4300 better than others. But hey if the weather is good, blast away with the Holley, they are a lot easier to tune.