Doesnt throttle all the way back down unless I press back on the throttle assembly at the throttle screw

[jsmits]

Stock carbs, K&N pods, 120 mains 42 pilots, new rubber boots. Got done replacing the float bowl gaskets and getting the carbs back on. I synced them again just to be safe, they were still mostly dead on. I've had this intermittent problem where the bike doesn't throttle back down. If I gun it it usually comes back down though, and if I press back on the throttle assembly where it meets the idle adjustment screw, apply pressure there, it will throttle back down.

Anyone have any ideas where my problem might be? This is my last real problem to wrap up on my bike and want to get it taken care of. Could it be the sync adjustments on the carbs? The nuts were really tight when I first got the bike and loosening and tightening those when syncing bends that bracket that holds the adjustment screw/nut. Could those being bent have something to do with it? I'm thinking it's possible because applying pressure when the tops are off directly to the slide lift assembly also brings it back down. Should I check the gap on these? If so, what gauge?

The slides come all the way back down it looks like as well. It's just very strange.

[TOOLS1]

What model carbs are you working on? I have seen this problem on the roundtop carbs. What happens is the adjustment not is too far down to start with. If you look at the factory service manual, it shows to start with just one thread showing at the top of the adjuster. Then you sync them to 7lbs. After that you adjust the idle with the main idle adjuster knob. Now all this is assuming that you have the roundtop carbs, and your cables, and throttle are not sticking.
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[jsmits]

This are the later model keyhole style 78 carbs. I have new throttle cables, but the push isn't hooked up because its about a centimeter too short. I think motion pro only makes one size for the entire 70s cb750 line and the push is a bit short and the pull a bit long mounted on mine. I have extra cable and nips I might try to to get the push working, because theoretically I can push down harder on the throttle to simulate the same pressure I apply when I have the tank off and I'm tuning it, and I push down on the throttle with my finger. It's very strange as it's intermittent and seems to get worse when it's real sticky outside. I'm going to keep examining them today since the weathers crap anyways. Maybe I can spot the problem.

[TOOLS1]

I have heard of people having problems with the MotionPro cables, but I have never experienced it. On the keyhole carbs, I always hook the push cable up first, then the pull.
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[jsmits]

Yeah I've noticed they've stopped offering them, probably because they couldn't support all the different configs these things had over the years. I have stuff I bought when I thought I might change out the throttle on this so I'll get the push going tomorrow.

It's most definitely the throttle assembly just being old and stiff. Fresh WD40 all down in the slides and all around the shafts and spring/throttle mechanism helps. After getting the idle tuned, lubing everything good and a storm cell moving through that dropped the humidity and cooled the air, it was hardly sticking at all. Keeping it lubed seems to be all I can do about it.

This winter... these carbs... gone. First thing I'm throwing money at lol.

[jsmits]

So after a night of failure (my soldering skills were rusty to say the least) and a second attempt tonight, I can confirm that an operational push cable fixes the problem completely. A gentle push back against the throttle when shes sticking idles it back down. Pushing too hard will actually idle the engine down almost to a stall as well, which is strange as well. Apparently you can push the throttles down further than their resting place.

These early CV carbs were a little over-engineered I think. The throttle assembly has a few too many moving parts and springs. I'll never figure out what, exactly, makes the slide needles stick a bit but this has solved all my headaches. Should have gotten the cable working sooner.

[Re-run]

I am not a fan for the motion pro cables. The honda cables are MUCH better, but you do pay for it.

I disconnected the push cable on my bike. It is still there in case the pull breaks. It seems like it is just slightly too short.