Sticky throttle

[54woody]

Finally got my car all back together after doing a major upgrade - 1275 midget engine, HS-4 carb, 5 speed Ford gearbox. Took it out for it's maiden voyage this afternoon and I've found a couple of more issues to sort out.

The first is that the throttle is "sticky" for lack of a better term. When the engine is cool, there is a slight bit of resistance when I first put my toe down on the pedal. It's enough that I can't really get a nice smooth acceleration. Rather, I get a sudden jerk as the initial friction is overcome and the throttle jumps open. It seems to get a bit worse as the engine heats up and at one point when I lifted my toe off the pedal to change gears, the engine kept going at the same speed rather than slowing. I had to give the pedal a tap and then it slowed back down.

The throttle cable is new - a teflon coated inner cable from the bicycle shop and a new outer sheath. The cable seems to slide fairly effortlessly inside the sheath, so I don't believe it's at fault. The HS-4 carb is new, a purchase I made off evil-bay about a year ago. Return spring is brand new and seem to work just fine. I've tried adjusting and fiddling with cable a couple of times and so far always get similar results. Could it be that the throttle shaft in the carb is biding slightly? Is that something that can be easily fixed? Looking for ideas as it doesn't feel quite safe to drive as it is.

[philthehill]

I would suggest that the Teflon sheathed inner cable is at fault.
I had the same fault, got rid of the sheathed inner cable and all was ok.
I just used a plain simple bicycle brake cable - outer cut to length and on the accelerator pedal end of the inner cable soldered a suitable nipple and soldered the carb end to stop it fraying. Job done.
I found that the sheathing of the inner cable was reeving up inside the outer cable and causing the cable to stick. A quick blip on the accelerator pedal temporarily freed it off and for a while it worked as normal until the next time it stuck.
You are right in that it could be dangerous so needs to be sorted sooner rather than too later.

[54woody]

Follow up...

I'm not certain, but I don't think the cable is to blame. I've taken the carb back off the car to give it a closer inspection. As soon as the throttle plate is open a bit, the whole throttle arm moves back and forth effortlessly. However, as the throttle plate closes, I can feel a very slight resistance such that when the plate is fully closed, it takes a bit of pressure on the arm to get it to start opening. THIS, I'm thinking, is not normal and is probably the source of the problem. Should there be ANY resistance to get the throttle arm to start moving when the plate is closed? Assuming this is the root cause, what would be causing it to 'stick' and how would I go about fixing it?

[bmcecosse]

No - it should swing freely.

[54woody]

Okay, that's what I thought. So why would there be resistance? Throttle plate not positioned properly? Is that even possible on an HS-4? Other ideas?

[philthehill]

If the cable is not to blame - is the butterfly central in the carb throat? The butterfly may have been disturbed (or even assembled incorrectly as you say it was new) and is not central it may be catching on the throat of the carb. The slightest out of alignment will cause the butterfly to catch on the throat of the carb and not go home or open properly and cause difficulty opening and closing the first and last couple of degrees. Loosen the butterfly securing screws open and close the throttle a couple of time see if it is any better, close the throttle and tighten the butterfly screws. That may be all the problem is.

[54woody]

I had a close look at the carb and it seems the throttle plate (disc) was not properly centered. It was lightly touching the body on one side as it closed causing just a wee bit of interference. After some minor adjustment, it now opens and closes smoothly. I'll put it all back on the car this evening and see what happens. Fingers crossed.

[54woody]

All back together. Took it for a drive today and the throttle is now operating smooth as expected. Cross another one off the list. Many thanks for your help.

[bmcecosse]

Well done !