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)

 

Okay so what happens with the car in park and you press on the gas do you get smooth throttle?

What happens when you added the tighter return springs?

my initial reaction is air flow over the plates is forcing them open due to weak return springs.

Another question If you were to tie a stick to the gas pedal so you could hold it with one hand and prevent it from going to the floor could you then accelerate smoothly through out the entire range?

Gun

 

You're gonna need a professional....

 

lol
"the power of Christ compels you!"

 

That was one of our first thoughts, we replace the springs it didnt make any difference, in park its very smooth, it dosnt happen even if im driving very slowly & blip the throttle only when I come to a complete stop & then pull away does it take off

We replaced the accelorator pump diaphrams but still no luck

 

Yes I Have considered darker forces at work!!!

 

Okay now im serious about the stick experiment. Give it a shot that way you can feel just how much force is pulling down on the pedal.

At rest require more work from the carb to get the vehicle to move so using the stick experiment you can feel those forces at work it may help explain some stuff or open up another avenue of thought.

Gun

 

Cheers, I'll give it a go tomorrow its nearly midnight here

 

I thought maybe lol.

Tie it just about center on the pedal and make sure you test and it gives full range before you start the car

Drill a hole through the end of the stick and run the rope or line through the hole so it doesn’t come off.

Let me know what you find I’m real curious about this

Gun

 

That is, without a doubt the strangest tail I have ever heard. I don't doubt it is true, but totally wierd. Have you considered an exorcism? Needless to say there has to be an explanation for all of this accelerating on its own. Ther are only so many things attached to the throttle that would open it up like that by itself or it is internal to the carb itself. Can't believe professionals couldn't fix it (although many "pros" are not that at all.

May the force be with you! (Apparently you already have the force - too much of it) Please let us all know what it is if and when you get it fixed.