1982 CB650SC Nighthawk Weird Throttle Issue

[Flarrow13]

Hello,

I am having a really weird issue with my 82 Nighthawk 650 that has to do with the throttle. Whenever I am idling and I give the bike throttle it hangs at about 3,000 rpm unless I pull back as far as I can on the throttle and hold it. Doing that will bring the idle back down to roughly 1500 rpm. When I just let the bike idle and do not hold the throttle back, the rpms will slowly creep up to that 3,000 point. Does anyone have any ideas as to why this could be happening and how to fix it?

[Bob H]

Need more info.
Was the bike running great - then this is a change?
Was the bike stored and you are bringing it back to life?

What history led up to this.
Fresh fuel? strong battery? what have you diagnosed so far.

[Flarrow13]

When I bought the bike it did not run at all, however this was due to a Carb issue. Rebuilt the carbs, but the bike would bog whenever you would give it throttle. This past winter, I did a complete overhaul and rebuilt everything. After doing that the bike ran great for about a week, and then the throttle issue began to happen. Fresh fuel, brand new battery. Thought maybe it was a carb issue. Synced the carbs, but issue is still persisting. Thought maybe it could be a sticky choke cable since I did notice that the choke cable is frayed a little right up by the knob.

[Larry Fine]

Either that or the throttle cable(s) binding due to being too tightly adjusted or mis-routed.

[Bob H]

... Thought maybe it could be a sticky choke cable since I did notice that the choke cable is frayed a little right up by the knob.

I don't have your model - but isn't that something you can visually confirm?
Even without starting the bike, it seems you could watch the action of the choke, and that it fully returns to "off".

On my 750, with carbs off a few months ago - that was the time to lube and inspect all cables including the choke. You bet pretty intimate with them doing a carb rebuild.

Whenever I am idling and I give the bike throttle it hangs at about 3,000 rpm

If that was my bike, and nothing else seemed to resolve it - I would get the bike up to operating temperature. Then I would disconnect the throttle cables and manually operate the throttle, the spring should snap the throttle back closed. It is a safety issue, carbs have pretty strong return springs. That would be a basic "black or white" diagnostic.

[Flarrow13]

I have checked to make sure that the choke is operating correctly and it does return all the way to the off position, I just didn't know if they fray in my choke cable could have something to do with it. Thinking about it now, when I bought the bike, the throttle was very sticky to the point where it would come back extremely slow which leads me to believe that maybe the throttle cable could have a bend somewhere which could be causing my issue. I'm very new to these bikes, so i'm not 100% sure.

[Bob H]

I have checked to make sure that the choke is operating correctly and it does return all the way to the off position, I just didn't know if they fray in my choke cable could have something to do with it.

Nope. Choke off = choke off.

...when I bought the bike, the throttle was very sticky to the point where it would come back extremely slow which leads me to believe that maybe the throttle cable could have a bend somewhere which could be causing my issue.

Did you lube the cable since buying the bike?
On my 750 it is a pain to detach the cables from the carbs. Maybe you can loosen the adjusters enough to detach from throttle and manually watch what is going on, friction - binding. Lube it.

[Larry Fine]

If it's just friction, you should be able to close the throttles by hand (twisting closed).

Have you checked the idle speed adjuster? We're presuming the carbs are properly synced.

[Flarrow13]

The Carbs are properly synced. It is a huge pain to get the cables off of the carburetors on my bike as well. However I will take them off and try to lube the cables.

[Bob H]

It is a huge pain to get the cables off of the carburetors ...However I will take them off and try to lube the cables.

That would not be my first step.
I would try from the handlebar end first.
I might pull the gas tank and carefully check the routing of the cables (you have to pull stuff to access the carb side anyway if you do have to disconnect from that end).

Routing cables is not as obvious as it may seem on any motorcycle, and I have learned to take photos from various angles before I remove anything. And check the manual, photos online, make sure the routing is OK.

Did you watch that video? I think he lubed from the handlebar end, and I have watched the lube drip out the cable from below. Work the cable back and forth to distribute the lube.

[Larry Fine]

From what I remember reading, Honda OEM cables are Teflon lined and supposedly do not require lubricating.

[Bob H]

From what I remember reading, Honda OEM cables are Teflon lined and supposedly do not require lubricating.

Well, one thing is for sure.
His "throttle was very sticky to the point where it would come back extremely slow" when he bought the bike.
Something needs to be done, and he is welcome to replace them (would involve the grief of carb attachment points etc.)

I just looked at all my cables a few months ago. Basically you just see the metal end and if there is a Teflon liner it is beyond that in a part you can't see.
Who knows, maybe they are Teflon lined.

I have heard not to lube Teflon liners, but this is from the OEM manual (2nd edition) for the NH 750



The main thing is to obtain smooth operating throttle, and in a perfect world this would have been 100% resolved when the carbs were off and everything easy to check out.

I have had cables bind just from being routed on the wrong side of the steering area.
And of course test the throttle with bars moved all the way over one side, then the other.

Some interesting comments on this Honda Forum, part way down some people are pretty familiar with Teflon (more than I am)
http://forums.sohc4.net/index.php?topic=172016.0

[mollusc]

I use silicone lube or chain lube for cables, with or without liners.
And you shouldn't need to remove the carbs to get the cables off them.  Long-nose pliers and/or locking surgical forceps work well to be able to get the stopper-ends out of their slots.