okay wierd problem. 66 shortbed with new rebuilt 390 from a 73, used C6 from a 76, power steering added, no power brakes. so i got it running great, broke in nice, idles smooth runs really nice when not moving. gets into gear fine, holds the idle and moves out of the garage great. the problem is when i decelerate and come to a stop. it start choking as i approach a final stop and dies when i stop, or even just before complete stop. the wierdest part is it'll do this in neutral too. i can coast half a block in neutral and it will idle just great, rev great, but when i come to stop it just dies. runs super through all the gears going down the road. thought vacuum at first but only vac is to tranny and pcv (dizzy is unilite no vac). checked the tranny modulator with a vacuum pump and it held vac fine for a long time. disconnected the pcv and plugged all ports. same thing. disconnected modulator, shifted funny, still died when coming to a stop in neutral or drive. chekced vac witha gauge, its good. this one is wierd: ran it in reverse and slammed on the brakes, stayed running. did this a few times after carb swaps wtc. still ran fine. it very much seems to be a forward momentum thing. so i adjusted the floats. reset the dle misture, rest idle.... to no avail. then i changed changed carbs! to the known great running holley off my falcon, same thing! re-adjusted floats on falcon carb while on truck, had to raise the float a bit on the front bowl, maybe a turn or 3/4 turn. but the rear bowl was like 3 or 4 turns before fuel started coming out of the sight plug. truck ran slightly better after this but still had the same issue 90% of the time). this second carb came from a car that would probabaly run 15 seconds just how the carb was set up.. but when i put it on the truck it needs significant adjustment? fuel pump is new stock mechanical unit, rebuilt from orieley/checker. filter is new. new lines, no leaks. 352 ran great with same carb and old fuel pump until throttle stuck and i overrevved it and it started knocking. actually ran great with the knock until i pulled it for the mildy built 390. anyway, im dumpfounded. seems to be a fuel delivary issue but 2 different carbs (600+/- cfm street avenger adn 750 cfm street avenger)acted exactly the same way.

any ideas greatly appreciated.

thanks

 

I would try a new fuel pump.

 

The RPM's are dropping too low when de-celerating, which is why the engine is sputtering...then dying.

What Ford did to compensate for this, was by using a dashpot on the carb linkage. It's adjustable, so once it's set at a certain RPM, the RPM's will not drop off when the carb linkage comes in contact with it.

If your carb has one...it may be defective. At the end of the dashpot where it contacts the carb linkage is a rubber boot...inside that is a coil spring. If the coil spring breaks, the dashpot no longer functions.

You can test the dashpot by pressing on the end of it...if it springs back, it's OK.

Or...if your carb has a dashpot, it may not be adjusted correctly.

btw: What Falcon V8 came with a Holley carburetor? None.

 

Try running it with the fuel cap of the tank and see if it does it still. You could also have a piece of junk on the bottom of the tank or a pin hole in the pickup line. How full is the tank?

 

These trucks use a vented fuel cap, because the tank is not vented.

If you use a NON-vented fuel cap...the tank may collapse.

 

Thanks.
Unfortunately its not an rpm issue. I can coast to a stop in neutral with my foot on the gas keeping the RPMs in the 2500 range and it still wants to die. in neutral, at high rpm, i can sometimes help it recover, but it does try really hard to stall. does not stall when going up hill or coming to a stop in reverese on level ground... wierd! niether carb has a dash pot as niether are stock, as you have gathered. they are both holley street avengers. the one from the car is 600 something and the trucks is a 750 cfm unit.

 

air harley, ill give it a try. im using a locking gas cap i got at lmc or something. had some gas siped a couple years ago. ive been running this cap for awhile, before the engine swap. tank is full, although tank was low when i first drove it, same problem. im thinking its something that i changed during the engine swap rather than something untouched that failed coincidentally. but i will definately check it out! need all the ideas i can get.

 

you didnot fool with any of the wires on the motor change did you ?? how about the pickup in the tank ??

 

I know this is a total shot in the dark. Did you reuse the same coil and if so how is it mounted and are all the connections/hardware tight? I am sitting here thinking about your situation with two carb performing the same way. It might not be a fuel deliver issue at all but an electrical one. Also the coil positive wire coming to from the firewall to the engine comes to mind. Double check the connection and insulation for a bad spot.

Bill the only reason I am suggesting the cap is I have had mine stop venting and it took me a little bit to figure out. If a mechanical fuel pump is installed it may colapse the tank (depending on age and strength), where as an electrical one wont. I happen to have an electrical one. I had about given up when I started the truck and drove off after I popped the cap off to look in the tank but didn't seat it all the way. Prior to that I would drive 10 minutes and it would crap out on me. Afterwards I drove all the way home a 30 minute trip and it performed flawlessly. Then I had to retrace my steps the last time I stalled and found the cap loose.

 

oldfordcoupe:
you know.. i did do some wiring. the alternator wires were shot to hell. bad splices, lots of cracking. they were so bad its a wonder it ran (i guess the oil all over them and the block was keeping them isolated) anyway, i did redo some of those. did not mess with the tank, or pickup or fuel line.

airharley:
same coil, mounted horizonatally on the intake. good thinking, ill start checking wires. thanks.

 

checked the wires. everything is fine as far as i can tell. have not swapped out a coil? but the one i have is pretty new. had it on the old engine for about a month or two before the engine was caput.

still no luck with this thing!

 

it was the coil! thanks air harley.

its mounted horizontally. should i remount it vertically?

 

I have seen both horizontal and vertical mountings but that is also dependent on the coil internals, solid state or oil filled. By the sounds of the problem I believe you have an oil filled model. With those they should be vertically mounted or you might be able to do so horizontally but the terminals should be straight up and down ( : ). I don't know about the horizontal mount for sure though as I normally run solid coils. The Accel 140008 can be seen in a few of my profile pictures before I swapped over the the HEI style distributor for my 460.

http://performanceparts.com/part.php?partID=5662

 

Try mounting the new coil on the fire wall. Heat kills and I have found new coils are not as forgiving as the older ones. Made off shore and all that. Just a suggestion

 

If you mount the coil to the firewall make sure you ground it to the engine as it will burn out the coil if its not. dutch