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Discussion Starter #1
I have a 1978 CB400A I am rebuilding, I just got done with the carb rebuild and I installed it along with new throttle cables. The old ones were frozen so I don't know how the throttle is supposed to 'act' on this bike.

On my old BSA lighting, when I let go of the throttle, it snaps back to its original position, and goes back to idle.

I am not ready to fire the CB400A yet, but I was playing with the throttle after I installed everything. This one seems to stick in place. When I let go it won't snap back to its original position. I cleaned up the twist grip a little thinking that was the problem, but nothing changed. Should this type of throttle snap back? My BSA throttle has a tensioner on it, so I could set it to stay in place if I chose, but I don't see anything like that on the Honda

I assumed all throttles just snapped back, or had tension adjustments - the Honda is only my second bike so I just want to be sure. I prefer it to let go when I let go. Do I Just need to clean it up more and lube it?

This bike has a Keihin VB24A carb if that makes any difference.

Thanks
Eric
 

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Not familiar with your model, but it should snap back. Is there a hang up at the carburetor spring area, or is it in the cable routing itself? Sometimes if the cable routing is too constricted, it binds up and freezes in place.
 

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I think the A models are the same as the other 400s, it should definitely snap back and it's probably due to adjustment. There's adjustment at the carbs and there's an adjustment on the handlebars. The service manual should help with which direction to turn them. I recall turning the handlebar adjuster clockwise (or so less threads show) making it looser (allows it the slack to snap back). Try all the way in and see if it snaps back, if not you might need to adjust at the carbs. Also make sure it still snaps back with the bars fully turned in both directions.
 

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Make sure your throttle isn't slid onto the handlebar too far. If the inside of the rubber hand grip is tight against the end of the handlebar, it will want to hang open and not snap back.
 

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If cable adjustment doesn’t help, remove the cables from the throttle tube/grip and see if it moves freely. If there is any debris inside the throttle tube or oxidation on the handlebars, it will hang up.
 

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I would suggest you change the cables unless you want to practice jumping off the bike when the throttle jams at high speed :D. Every throttle needs to return to idle after you let go.
 

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I would suggest you change the cables unless you want to practice jumping off the bike when the throttle jams at high speed :D. Every throttle needs to return to idle after you let go.
In case you don't realize, his bike has push-pull throttle cables that can be rotated back to idle forcibly if necessary... plus the usual kill switch and ignition switch as well, so bailing isn't likely necessary. But it sounded dramatic. :D
 

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I dont know how you ran your cables but I found on my A that if you remove the left top motor mount and run the cables between the top mounts they work a lot better. Going around the left mount puts them in a bind. Having worked on several As I KNOW its a lot of work but I would pull the carbs back off , put all the cables on and see how they work ,if ok I would reinstall the carbs with the cables in between the upper mounts.

Hope this helps.

Bill
 

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There needs to be a little bit of slack in the cables(1 mm or so) if they're pulling against each other things will bind.
 

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I dont know how you ran your cables but I found on my A that if you remove the left top motor mount and run the cables between the top mounts they work a lot better. Going around the left mount puts them in a bind. Having worked on several As I KNOW its a lot of work but I would pull the carbs back off , put all the cables on and see how they work ,if ok I would reinstall the carbs with the cables in between the upper mounts.

Hope this helps.

Bill
I was thinking of doing that routing with my new cable. It doesn't bind but I have it routed thru the center of the trees and around the left side and when I turn the bars left it hangs up on the left riser mount bolt. I was thinking that a zip tie to center backbone of the frame would keep it from hanging up but through the top mount would center it better and look cleaner too. Thanks for that tip Bill
 

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The cables don't go thru the triples, they run over the front and around the left side
 

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When I replace both of my throttle cables with ones from motion pro, they were VERY susceptable to becoming hung up with internal friction following the stock routing. I also pre lubed them with cable lube as instructed as well. I left the carb ends off and found a routing that provided the snap your looking for. I was not able to use the stock routing hanger as it comes off the handlebar, mine had to "go more forward" before sweeping back on the left side frame. I forget if I put them inside or outside of the engine top mount. I'll check and take a picture of what i did and post tomorrow if I remember before work. I do remember thinking to myself that the factory cables allowed for tighter bends in routing than the motion pre replacements...
 

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Discussion Starter #15
Been a while since I got to this but I found the culprit! Heavy rust buildup in the end if the handle bar was making it stick. Works like a charm now!


Sent from my Pixel 2 using Tapatalk
 

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Wow that is gross! Thanks for posting a "conclusion". Now we know of one more condition to check with a sticky throttle. Did you manage to get it cleaned up? Planning to sand it and coat it to mitigate re-buildup?
 

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Discussion Starter #17
Wow that is gross! Thanks for posting a "conclusion". Now we know of one more condition to check with a sticky throttle. Did you manage to get it cleaned up? Planning to sand it and coat it to mitigate re-buildup?
I sanded and sprayed with oil for now. I will keep an eye on it, but the bars are rusty to begin with so I will replace it eventually with a nicer one.
 

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I thought this seemed like a logical place to post this question. If there's no follow-up, I may start another thread. Not sure what the protocol is.

Anyway, I'm having an issue with a sticky throttle as well. Is there a trick to pulling off the grip and throttle tube to check? I wouldn't be surprised if the end of my handlebar looks like the one in the pic, but I can't easily pry it off and I don't want to force it and end up breaking something. Is there some kind of spring that returns the throttle? When I'm riding and let go, the throttle definitely returns, but upon start up, I can easily make it stick to force a higher idle. Seems sticky more than anything else.

Thanks for your thoughts.
 

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I thought this seemed like a logical place to post this question. If there's no follow-up, I may start another thread. Not sure what the protocol is.

Anyway, I'm having an issue with a sticky throttle as well. Is there a trick to pulling off the grip and throttle tube to check? I wouldn't be surprised if the end of my handlebar looks like the one in the pic, but I can't easily pry it off and I don't want to force it and end up breaking something. Is there some kind of spring that returns the throttle? When I'm riding and let go, the throttle definitely returns, but upon start up, I can easily make it stick to force a higher idle. Seems sticky more than anything else.

Thanks for your thoughts.
Remove the screws holding the housing together and pull it apart. Remove the end of the cable from the plastic throttle sleeve, and then the sleeve should slide right off the bar. The return spring is on the carb.
 

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Thanks for that info. I might as well try to lube the cables once I get that housing apart, too. Wondering if I should just get new grips and throttle tube. I guess it will depend on the condition of the existing.
 
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