Andyjamo

My 67 Fastback has a very dangerous fault that I and my repair shop cannot fix after 2 months of scratching heads

car is a 67 Fastback with a newly rebuilt (12mos) 351 Windsor, C4 Auto also rebuilt, and new at time of build 750 Holley double pumper, in fact everything is either brand new or rebuilt

From stop even the most gentle move from stop results in the accelerator pedal going flat to the floor and the car goes into full acceleration momentarily, gradually getting longer and more dangerous.

This only happens when the car has came to a complete stop, we’ve stripped the carb, the accelerator linkage, kick down mechanism, in fact everything we can think of including a stronger carb return spring but the problem keeps getting worse.

Can any of you guys shed any light on this or suggest a solution

Cheers

Andy Jamieson (Silverstone England)

Tim37

wow thats really wierd the only thing i could think of that might cause that and i have never even heard of this happening is the car pulling so much air that its opening the carbs butter flies but i really dont' see that happening are you sure your shift linkage isn't interfering with the throttle when its in gear.

man thats just really wierd.

Andyjamo

The carb is not that old less than 10,000 miles, though the problem has got from being an irritaion to a real problem in a couple of months. weve stripped the carb and found absolutely no problem with any parts!

Dan04COBRA

I'm sure someone has a donor carb you can use. Simply swap carbs and eliminate that. Work from there.

Sounds to me like there is a linkage issue.

wildcobrar

A 67 Mustang would not have come with a 9.5 inch tall deck motor. It more than likely had the 8.2 inch tall 289. I believe these cars to have a mechanicl linkage toi the carb(all rods and such) I would try to work a modern day cable from a carbed 351 Crown Vic with the cable bracket that holds the cable but bolts to the back of the intake right over cylinder #8.

newbikerider2003

Double check that after final assembly. Nothing can touch the moving parts of the linkage. When I put a Holley on 2 of my motors I added a return spring. Always found that the return spring coiled around the shaft as too weak. Ran it from the throttle on the carb in as straight a line as possible to a bracket. I also use cables not the 60's style linkage.
The 1970 Torino had a return spring built into the cable and the mount, bolts to the V8 intake. Even after market intakes usually have the same threaded mount holes. It was a style Ford used in many cars through 70's and early 80's.

393Bird

See if it does it in reverse. If is does not, your left motor mount is shot. If the motor mount is broke, it allows that side to rise up under load, and pulls the throttle open while it does it. Newer cars have a saftey device built into there mounts that will not all more than about a 1/2 inch of movement.

Tim37

yeah that makes the most sence so far.