Touchy Accelerator

[Thodge]

I’m trying to find a solution for the touchy throttle on my dad’s coupe. I know that the footrest was the original solution to the problem but he has a problem using it. It’s uncomfortable to use and his foot gets caught under it if he doesn’t use it. We took the footrest out completely but you really have to use a light touch on the pedal or there’s a lot of bucking and jerking when getting on the throttle in first and second. Do the accessory Fulton-style pedals help with this? I was also wondering if there’s a way to add an extra return spring on the throttle linkage or if that would even help.

[Gary WA]

The spring on the throttle linkage may be worn!?I'm sure if you could fit an extra spring may help.

[Phil Brown]

A little oil on the linkage might smoth things out as well, don't forget the shaft that run's behind the block

[Brentwood Bob]

replace with a block of wood?

[Y-Blockhead]

Your Dad isn't the only one. I have often thought about changing the ratio of the linkage to slow the movement at the carburetor compared to the movement at the foot.

But that is as far as I got, thinking about it.

[Thodge]

Sponsored Links (Register now to hide all advertisements)

I was looking at options for changing the linkage ratio because I agree that it should have been a much slower ratio originally. I think the problem stems from where they put the ball on the carb butterfly lever. When the throttle is closed, the ball is almost directly behind the throttle shaft. This makes the ratio very high when the throttle is first opened because the linkage rod is nearly pushing straight toward the throttle shaft and that translates to a higher number of degrees opening in relation to forward motion. It would have been better if they originally put the ball directly below the throttle shaft which would have made it increase progressively as the throttle opened. The first thing I may try is putting an additional compression spring between the floorboard and pedal button and see if that helps any.

[nkaminar]

My friend has the Fulton style foot pedal and likes it a lot. He drives on long trips and just completed a 3,000 mile journey in his 30 coup.

I use the hand throttle a lot. It is handy when starting out on an up hill traffic light with someone right behind me. My Model T only had the hand throttle, no "foot feed" as it used to be called.

[Thodge]

That’s good to know. Might try that if I can’t come up with any other solutions.

[1crosscut]

I’m with Bob on this one. A block of wood screwed down to the floor would solve the issue with his foot getting caught under a foot rest. Many different thicknesses and shapes are possible for making using the gas pedal better.
I’ve tried driving without a foot rest and it’s a pain (to me at least)

[Thodge]

We’ll have to experiment with the wood block solution. Any suggestions on a starting point for the height of a footrest? I always felt that footrest that was in this car was too high no matter what I did. First, it was because when they made the replacement floorboard, they never drilled the hole for the footrest stud to go through. I drilled that out and lowered the rest all the way down to the jam nut and it was still too high. Then I removed the jam nut and just bottomed the threads out on the bracket and it was acceptable for me to drive it but he was still having problems with it. I would guess at its lowest point this rest was still 1” to 1-1/4” high off the floor. I doubt if it is original or even an accurate reproduction.

[RDVAARK]

Think of the linkage as a chain of levers. The first is the pedal pad to the shaft crossing the rear of the engine. Lengthening it will slow foot travel's effect on the shaft, and slow down engine speed response-less touchy. A long set screw, or a short section of threaded rod with a connecting nut, on to the section sticking out of the floor, can do this.
Similar effect can be to lengthen the arm on the butterfly shaft. slowing its speed and allowing finer adjustment (speed governors often use this).
The object is to coordinate the position of the butterfly at cruising speed to the position of the pedal pad that is easiest to hold steady.
Explanations can be found in physics texts explaining lever systems. Another could be found in the piston vertical travel speed versus crankshaft position in an engine. Piston speed is max at 90 degrees ATDC, and 270 ATDC. Effort to tun the crank is at the minimum. Hand cranking the engine from 270 or 90 is easiest, harder from TDC or 180.
Enough confusion from me. Could someone else please elaborate to make this clear?
Russ

[1930artdeco]

I have an original 'Fulton style' gas pedal and I love it except the angle between the button and pedal needs to be just right. Mine is off just enough that it can be hard to get it to accelerate from a stop. But once it gets going then it is great. It all comes down to that initial angle between the button and the flat spot on the pedal.

Mike

[Thodge]

The easiest way to think of it is that the throttle shaft and lever are effectively a crankshaft and the linkage rod is like a connecting rod. Like you say with a crankshaft spinning a constant speed, the pistons move fastest at 90 and 270. The only difference is that the work is being applied in the opposite direction so 90 and 270 above and below the throttle shaft would give the slowest opening of the butterfly.
The tricky thing in changing the overall ratio of the linkage would be keeping enough travel to fully open the throttle. You would need to tweak the lengths of every lever in the system together or you’d end up with a very high pedal off the floor.

[Brentwood Bob]

Working around a floor Matt will complicate using a wood block. I assume you have bare wood floor boards with no Matt, or rug. Start wth a 2 by 4 , flat, then shave to suit. I would
Think the original factory foot rest is optimum height. Setting a high idle with the factory column lever you loose the finesse of smooth start(launch if you will). Hard to see from here what issues your father has with his foot, and if he wears open toed shoes.
My thoughts. Bob.

[Brentwood Bob]

There is another possibility, although you said you are able to use the foot feed. When the motor is removed the throttle linkage can get mangled, specifically, the assembly
bolted to the flywheel housing.
You would need a complete, correct assembly to compare to yours.

[Thodge]

The car does have a rug so that does pose a bit of a problem with using a big block of wood on the floor. I think the problem that we’re having with the footrest is that we’re both tall, have big feet, and it’s a coupe. You are limited as to how much you can roll your foot when your knee is jammed in between the steering column and the shifter. It’s easiest to just use your toe on the pedal button but that obviously makes it more difficult to be smooth.

[Brentwood Bob]

I'm built more like the typical 1931 driver, just chubby. Smaller, narrower seat might help a little. I'd pull the rug out, and go bare floor board to test the wood block, or even pulling the floor board to check the throttle assembly. The spring could be damaged.

[Thodge]

Yes, making the seat back narrower would definitely help. It might be time to remove the upholstery and tie down the springs some. We’ve already raised the rear of the seat on the tracks by 1” which let us move it back further before hitting the package tray. Now it’s reasonably comfortable and much better than how undriveable it was in the original location.
The throttle linkage is undamaged and works perfectly so I really think everything is working the way it was intended. They just didnÂ’t intend for Bigfoot to drive it. I plan to experiment with compression springs of various stiffness mounted between the pedal button and the floorboard and hopefully that helps smooth things out.