Throttle cable friction - Could it be caused by loose (wobbly) pipe on top of carburetor?

Dave Kinskey

New Member
Hi. My 1969 CT70 K0 has a new throttle cable, and although the throttle has always stuck ("cruise control"), I've noticed a lot more friction. The top of the carburetor did not have the gasket previously, but now has a rubber gasket. The pipe that goes into the carburetor top (the carb "cap") has a lot of wiggle (or wobble) to it, so it can move when throttle cable tension occurs. I've attached photos, showing how much it can move.

I'm wondering if the cable is rubbing against an inner part of the "cap", creating the friction because the cable is not going "straight down", and maybe I need to buy a new carburetor top piece. When the cable is out of the pipe, it moves smoothly and freely, but when the cable goes through the pipe, there is a lot of friction and resistance, which I can even hear (besides feel) in the throttle assembly, or even with throttle disassembled, just pulling on the cable.

Is the amount of wiggle (or wobble) in the pipe coming out of the cap normal, as seen in the photos? Also, I'm wondering if there should be a small gasket in the brass part at the top of the pipe, where the throttle cable inserts.
 

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lukelaw1

Active Member
There should be a rubber boot that goes over that tube, which kind of holds the tube "centered" and the cable into the brass nut in your last photo. IMO the whole Honda ct70 throttle setup was lacking engineering. your best test would be, take the cable off at the handlebar leave the carb end hooked up and see if you can cycle the cable and have the carb slide will retract on its own. The flaw is in the handlebar horizontal slide setup to much drag and not enough spring in the carb cap.
 

b52bombardier1

Well-Known Member
Try slightly loosening the carb to manifold flange bolts. With these a little too tight, the body of the carb warps and squeezes on the throttle slide.

And Voila!! We have inadvertent cruise control.

Rick
 

Dave Kinskey

New Member
There should be a rubber boot that goes over that tube, which kind of holds the tube "centered" and the cable into the brass nut in your last photo. IMO the whole Honda ct70 throttle setup was lacking engineering. your best test would be, take the cable off at the handlebar leave the carb end hooked up and see if you can cycle the cable and have the carb slide will retract on its own. The flaw is in the handlebar horizontal slide setup to much drag and not enough spring in the carb cap.
Thank you. Yes, there is a rubber boot, a recent replacement. With the metal throttle grip tube removed from the handlebar, using just the throttle slide, even with the boot on the carb top piece, there is a lot of friction in the throttle cable. However, when the cable is not threaded through the pipe of the top piece, the cable moves very freely, without resistance, using just the slide in the handlebar. The friction seems to be caused by top piece pipe, perhaps greatly increased by just the curve, if not due to movement of the base of the pipe.
 

Dave Kinskey

New Member
It may sound sacrilegious, but a switch to a cheap Chinese aftermarket throttle will solve all your problems.
Yeah, I can't say that I haven't considered it, but that would be a last resort. I finally got the carb nicely tuned, and a new float needle, seat, and seal, so the float bowl stops flooding, which caused it to run very rich and foul plugs very quickly. If I can now get the throttle cable to operate smoothly, I can keep the original carb on the bike. Fingers crossed. :)
 

Dave Kinskey

New Member
Try slightly loosening the carb to manifold flange bolts. With these a little too tight, the body of the carb warps and squeezes on the throttle slide.

And Voila!! We have inadvertent cruise control.

Rick
Thanks, Rick. That's very interesting. I had not heard of that. I will make sure to keep it in mind, but since the problem occurs when the top piece is removed from the carb, I think it's probably not the cause in this case. With cable removed from the top piece, everything slides smooth and easy, without a lot of friction or resistance, just moving the throttle slide in the handlebar. As soon as the cable is installed through the tube of the top piece, with top piece not installed onto the carb, there is a lot of friction and resistance in the throttle cable, with or without the spring, the slide, and needle installed onto the top piece.
 

Dave Kinskey

New Member
GOOD NEWS! Fiddling with the cable and connections, using more Motion Pro cable lube spray in the cable, and using Motion Pro cable lube spray to lubricate the handlebar, the slide, the retainer ring, and the inside of the metal throttle grip tube, significantly reduced the friction. Enough so, that it allowed me to reinstall my Throttle Snap Back kit from Vintage Honda Minis, and got it to work now. There was too much cable friction before. Josh Eule of Vintage Honda Minis has made a great invention, which uses a spring and a custom-made piece, etc., inside the handlebar to push back the throttle slide when you let go of the throttle. Works like a charm now! No more "cruise control". :)
 
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