Topic: Sticky Throttle

[bleuquila]

Okay, next problem: The throttle return isn't so good - I can open it up, but it doesn't reset very well, but I can't figure out where it's getting stuck.  It almost looks like the problem is at the carbs, they just don't close all the way unless you turn the handle by hand, just thought I'd fish for suggestions.
My theories are:
The carbs are sticking open somehow
The cables are binding
The return spring is shot
the handle (rubber grip part) is sticking

Anything else? where should I start?  I did pull the cables off yesterday and they seemed to move freely and without restriction, so I lubed them and reinstalled, with no noticable improvement.  So I think I can cross that one off.
 The carbs were dipped to clean them out, buuuuuut I didn't oil/lube/grease any of the bits before putting it all back on the bike.  So maybe that's my problem?  If it's the return spring, is there any good way to get at that w/o taking everything apart, and without knowing what the spring rate is / shold be how would I determine if that's the problem?

 This is an annoying problem, and it's an understatement to say that a sticky throttle makes me nervous.

[TwoTired]

Under the throttle grip is a thumb screw that sets throttle friction.

Have you loosened this?

[MetalHead550]

I had the same situation on mine when I first got it.  I wd40'd every moving part in the throttle/carb linkage and took off the top cover on my right hand controls and gave a good shot down the throttle cables themselves then, with the gas off of course, worked the throttle till my wrist was cramped and it works great.  Youll probably want to do a process of elimination on the things you listed but my guess is the throttle cables are dragging in their casing and need lubed or you may need new ones.

[Greg]

also check that the throttle cables are not pinched by the gas tank -- mine were and freeing it up made all the difference
greg

[migopod]

I agree with greg.  I had bindage after re-fitting to clubman bars, and it was all in routing
under the tank.

One neat test to do is to check if the friction changes when the steering position
is changing, or if the return still isn't working when the tank is removed.
 

[bleuquila]

Hmmm, okay I'll double-check the cables, but as I said I removed them completely yesterday and lubed them till a stream trickled out the other end and put them back - no pinching or binding that I can see. The tank isn't actually fully installed at this point, it's just resting in place, on top of the rubber mount.

 I didn't know there was a thumb screw, however!  Under the grip, you say?  As in, I need to remove the grip first, or it should be visible ?

[dusterdude]

between the cables

[Jonesy]

The throttle friction adjustment screw is a huge knurled knob sticking out of the bottom of the right-hand control pod between where the push-pull cables come out. There is a little plastic "brake shoe" inside that rides against the plastic throttle sleeve.

Also, did you check the throttle slide actuator for freedom of movement? Is the shaft binding? There are felt washers next to the bushings that hold oil and one maintaince item is to oil the shaft to keep it free.

Oops.. I now see you have a cb500.. don't know if this is the same throttle setup (I was thinking 750)

[TwoTired]

I didn't know there was a thumb screw, however! Under the grip, you say? As in, I need to remove the grip first, or it should be visible ?

Yeah, I went out and looked at my 72.  Hangs down in plain view.  Well in the shadow of the grip housing, anyway. There's a spring on it.  My 74 has one, too.  It's kind of a cruise control sometimes on long freeway stretches.  And, it is sometimes nice to use on a cold day during warm up, while you are putting on the gloves, etc.

[migopod]

If you're not bending the cables on a tight radius, and they're clearly not pinched under the tank, how much
spring tension is there if you work the throttle by hand on the carb end, and does it snap back to closed without the
cables attached?  All the SOHC4 carbs i've messed with (all 550's) have had a very tight throttle return spring, and have snapped
back to closed hard and fast.

I also don't have a friction adjustment screw on my throttle pod, so that might not be there.

[MetalHead550]

I did pull the cables off yesterday and they seemed to move freely and without restriction, so I lubed them and reinstalled, with no noticable improvement.  So I think I can cross that one off.

Well hell!  Sorry for the pointless comment then.  I read carbs instead of cables.   Process of elimination indeed...but hose down all the moving parts on the carbs you can observe while twisting the throttle.

[Bob Wessner]

Until you get it sorted out, make sure the old kill switch is working. Hope not, but you never know the condition could get worse, as in stick farther up the power band.

[eldar]

The cables could be worn on the inside of the sheathes. If this is the case, no amount of lube will really help. This happened with my clutch and it was almost impossible to pull in with one hand. My throttle is stiff like this too. I dont have a adjustment knob on my grip and my carbwill snap shut with some serious power with out the cables attached. So if lube does not work and there is no binding from routing, I would say to get new cables. Just keep the old ones for spares, just in case.

[bleuquila]

Glad other people have chimed in, I was going nuts looking for that thumb screw! 

I'll try this evening at the carb end without aid of the cables, that's a good idea.

[TwoTired]

I really wasn't telling stories,  I have two bikes with the friction knobs, I thought all the bikes came stock with them until 1975.

[bleuquila]

Update:

Well, I'm slightly discouraged.  It's definately not the cables, I took them off at the carb end, and moved the throttle by hand, it gets stuck quite badly at the point where the carb ... tops.. start to rise up.  I played with the throttle on a 650, I see what you mean it has a very satisfying *snap* closed, mine is worlds from that.  Feels like something is binding, and there's a bit of a sound when I lean my ear against the right-most carb.. not sure how much operational noise is standard.

I tried dousing them in marvels mystery oil, and twisting the grip till my wrist locked up, and didn't make a lick of difference.

So.  I'm afraid I'll have to take the carbs out and break them down till I can figure out what part isn't moving right.  Bah!!

[dusterdude]

aint carbs fun

[amamet]

might be a long shot but i had the same problem on my 74 ducati 750 gt.  problem was lube somehow got past cables and weeped into carbs and slides were sticky from the lube which inturn didn't move freely against the carb walls.  had to clean them real well twice to stop them from sticking.  hope that helps

[Zeke]

Two things,

My bike is a 650 and when you insert the throttle shaft into the #3 carb you have to preload the return spring (it's a torsion spring) almost a full turn before you hook it on -- this took a good effort.  If you have this arrangement and don't have the spring on correctly you'll get no return.

Other thing, is that if you inadvertantly scored your carb slide with a screwdriver or something it might stick.

A friend of mine in high school did this, after he had permanently hotwired his old 250 enduro by removing the key -- it did not have a working kill switch.  The throttle stuck full open and I was sure he was gonna die as he disappeared down an abandoned railroad grade....Luckily he was able to shut off the fuel and the bike died shortly after before killing him.

Took alot of steel wool to remove the scratch....

[bleuquila]

Hmmm, yeah the spring is an interesting point.  Since I can't get at it until I pull them off the bike again, no way to tell now, but there's a chance it's either too weak, or apparently not on there right.  can anyone confirm that for a 72 500 there would be pre-loading of the spring required?

A friend of mine reassembled the carbs after we dipped them, which I regret, since I can't personally verify that everything went back right. It ran, so I took that as a good sign   but, he didn't have any more idea what he was doing than I do, so who knows.

[tgascon]

How'd you make out with the throlltle return spring off!
I had the same problem with my 1975 CB550K after I had them rebuilt.(carbs)
They were all bench Synched by the mecanic for me and would stick, especially a near the top.
Ater scratching my head for a while and ensuring the cables(new) were routed properly, I removed the throttle return srping and still had the same problem.
I then removed the top of each carburator(2 screws), noticed that if you push down on each throttle arm then is some spring resistance. But my # 3 carb was solid, no movement at all.  I removed the arm and throttle set and discovered the carb sink adjustment screw was pinching the lower knuckle on the Arm set.(could hardly move it)  I just backed the sync screw off a tad and presto nice and smooth again.
Then I just ensured carb sync was carefully adjusted to prevent pinching of the kuckle.
I put the return spring back on and the throttle snaps back!

Thought it might help!