Throttle Cable / Carb issue? *Victory!

[stormi]

Alright.  The wiring diagrams be damned.  
 
I routed the throttle cable straight up from the carbs to the front of the bike.  Fed it through the clamps to the throttle grip, and tightened everything up.  This means that there's only one bend in the cable, rather than the several introduced by the "recommended" routing.

One little snag when I tightened everything too tight against the bar end (free cruise control).  Fixed that, and wheeled her outside for a bath.  (Just waiting for some shade now.)

If you turn her bars all the way to the left, she bumps her idle up to about 2k rpm (from 1500) , but holds there.  All the way to the right, no change from idle.  I can live with that.  

Now to spend some time breaking this engine in and get some hours on her.    

Should be nice when the other half gets home and doesn't have to fight with her.  Maybe he'll put his CR250 back together, and we'll have some room in the shed again.   two bikes in pieces really take up a lot more room than when they're together.

[PitterB4]

Seems to me, if you have to reinvent the routing, something is still wrong somewhere.  Lock-to-lock, there should be no change in your idle.  

BTW - sorry about those canuck comments in Off Topic.    

[stormi]

Seems to me, if you have to reinvent the routing, something is still wrong somewhere.  Lock-to-lock, there should be no change in your idle.  

BTW - sorry about those canuck comments in Off Topic.    

Yeah,.. I think so too,.. but apparently the bars I just put on her are wider, I didn't think they were.  I do know that the rise is lower, so maybe the bar change forced a change in routing.  

Which canuck comment are we referring to?  

[erik]

I found out what was causing my bike to stop when I got home and turned around on the drive (downhill and turning the bars to the left).
The choke cable was a bit tight and was pulling the choke when the bars were turned.
I think the tendency for the throttle to stick when moving the bars to the right might have reduced as well, but I don't know if that's due to loosening the choke cable or not.

[Squishy]

Interesting..  I know this is an old thread but i've been battling this issue with my bandit 400 for 12 years.

I bought a new OEM cable, didn't solve it.
Tried every possible routing, didn't solve. I even had the cable directly from the carb to my throttle, straight through the air, and it would still do it.

It does not shoot up in RPM when I'm not touching the throttle. Instead, it only happens when I'm already on the throttle, e.g. 10km/h constant throttle. If I now move my handlebar to the right, it shoots me from 10km/ to 30kmh.

I think the issue is because the 400 only has 1 cable and no return. I can literally reproduce the issue with a bare cable (not connected to anything), then holding one end of the cable, and bending it slightly. The other end of the cable will move almost 1mm - and therefore twist the throttle plate.

I even had a custom cable made but it makes no difference. I have no idea how to fix this... I would like to use my 40 for moto gymkhana but this issue literally prevents me from it

[stormi]

Do you know if you have the original bars or if they've been replaced with a different bend?  That seemed to be the bulk of my issue. The smallest change in the distance that cable needs to travel seems to play havoc.

I feel like the shielding is a little too long for the cable.  The slack it has should be greater and able to be taken up with adjustment.  Instead, the cable has no leeway and jerks the idle up.

I always thought Gymkhana would rely mostly on clutch control - but I suppose that sudden rpm changes could be disruptive.

[Squishy]

Do you know if you have the original bars or if they've been replaced with a different bend?  That seemed to be the bulk of my issue. The smallest change in the distance that cable needs to travel seems to play havoc.

I feel like the shielding is a little too long for the cable.  The slack it has should be greater and able to be taken up with adjustment.  Instead, the cable has no leeway and jerks the idle up.

I always thought Gymkhana would rely mostly on clutch control - but I suppose that sudden rpm changes could be disruptive.

I have the original bars. Bike is completely stock except the muffler.
Last week i've had a custom cable made, it's 15cm longer and with a tinner outer cable, but it made no difference. The cable hardly moves at all, doesn't touch anything but the slightest movement makes rpm shoot up.

What do you mean exactly no leeway? You think the outer cable should be longer relative to the inner cable?

No Motogymkhana is all throttle and rear brake. No clutch. It's very disruptive because I literally shoot out the corner in 1st gear very low speeds.

[stormi]

What do you mean exactly no leeway? You think the outer cable should be longer relative to the inner cable?

No Motogymkhana is all throttle and rear brake. No clutch. It's very disruptive because I literally shoot out the corner in 1st gear very low speeds.

Exactly the opposite.  I felt like the outer cable sheathing was too long. So if you have 1cm of inner cable on the carb end and 1cm on the bar end, I feel like it would do better with maybe (as a completely arbitrary number here because I can't even reference the bike because I don't own it anymore) another 1/2 cm in total length.  That would let you assemble it AND take up some slack using the adjustment.  As it sits with the stock cable - by the time you assemble it, there's zero slack to take up with the fine adjustment at the bar - meaning that adjustment ability is useless and - ultimately - needed if the cable were a better length and it could be assembled properly so that installing the tank couldn't raise the RPM or turning the bars or looking at the
bike while Mercury's in retrograde or whatever.

I remember that throttle cable being the most fiddly cable to ever reinstall for the same reason.  It was a bear to do even if you did it 100% right.

[Squishy]

What do you mean exactly no leeway? You think the outer cable should be longer relative to the inner cable?

No Motogymkhana is all throttle and rear brake. No clutch. It's very disruptive because I literally shoot out the corner in 1st gear very low speeds.

Exactly the opposite.  I felt like the outer cable sheathing was too long. So if you have 1cm of inner cable on the carb end and 1cm on the bar end, I feel like it would do better with maybe (as a completely arbitrary number here because I can't even reference the bike because I don't own it anymore) another 1/2 cm in total length.  That would let you assemble it AND take up some slack using the adjustment.  As it sits with the stock cable - by the time you assemble it, there's zero slack to take up with the fine adjustment at the bar - meaning that adjustment ability is useless and - ultimately - needed if the cable were a better length and it could be assembled properly so that installing the tank couldn't raise the RPM or turning the bars or looking at the
bike while Mercury's in retrograde or whatever.

I remember that throttle cable being the most fiddly cable to ever reinstall for the same reason.  It was a bear to do even if you did it 100% right.

Yes that's true, I always had the adjustment all the way max out (max slack) or close to it.
That said, I'm not sure if giving it more slack would solve my problem, because when you're on the throttle there is no slack.

Also, I have 2 other throttle cables lying around from other bikes. If I hold/pinch the cable steady on the throttle side, simulating i'm holding steady throttle, and then bend the cable in mid-air, I can see the throttle-end moving 0.5-1mm.
Just this fact, tells me it's not at all about cable routing or slack. All 3 cables I have do it disconnected from the bike.
I'm starting to think 1 throttle-cabled-bikes are just not really suitable for slow technical turns let alone motogymkhana.

[stormi]

Yes that's true, I always had the adjustment all the way max out (max slack) or close to it.
That said, I'm not sure if giving it more slack would solve my problem, because when you're on the throttle there is no slack.

Also, I have 2 other throttle cables lying around from other bikes. If I hold/pinch the cable steady on the throttle side, simulating i'm holding steady throttle, and then bend the cable in mid-air, I can see the throttle-end moving 0.5-1mm.
Just this fact, tells me it's not at all about cable routing or slack. All 3 cables I have do it disconnected from the bike.
I'm starting to think 1 throttle-cabled-bikes are just not really suitable for slow technical turns let alone motogymkhana.

If you have room to adjust it for more slack - it should lessen your issue.  I never had any adjustment to gain slack on my b4.  Ever.  The cable isn't long enough.

You wouldn't necessarily be giving it more slack - you'd be giving it proper slack to be able to absorb the movement of the cable from the tank being put on it (yeah - watch it when you put the tank on if the cable isn't attached at the throttle end.  You'll see it shorten), or your "bending the cable", or even the natural couple of mm of freeplay that a throttle cable should have.  The cable on my b4 had no slack or freeplay. None.   
 
All cables will shorten if you bend their sheathing.  That's expected.  Free play allows that to happen without it causing the motor to rev at the same time.  Free play also lets you hit a bump and have your right hand move without causing you to whiskey throttle it.

I'm obviously not being clear.  Think of walking a dog.  If you walk with the leash with adequate "slack", the dog can turn its head and look at things without jerking your arm around but you still have control if he tries to take off.  If you walk with a choke hold, as soon as he turns his head he's going to jerk your arm, right?  This is the same as bending your cable in mid air and watching the throttle end move when there's no slack at all or what happens when you turn the bars and the idle rises.

Try this: https://www.youtube.com/watch?v=zy2dj9VvEdI  - Ari talks about the cable lengthening with age - which is why you'd usually make a fine or gross adjustment of the throttle cable.  If you look in the comments, "Rowdy Bikes" says they like 0.0mm free play.  Notice the first response?  "Yup - as long as it doesn't rev when the bars are turned,"

Ari also mentions at the end that you need to re-adjust if the idle goes up when you turn the bars. (Because that means that the cable is adjusted too tightly and needs to be backed off)  What he can't know is that there's no way on the B4 to back off your adjustment that's too tight because there's no adjustment built into this cable because it's too short to begin with.  The cable is too short in relation to the sheathing thus no freeplay, and no forgiveness when turning the bars.


In fact, we simulated this exact issue on that dirt bike in my signature.  The carb was assembled with an incorrect jet needle (too tall) while my other half put a JD jet kit in (because I really needed that much extra power and throttle response on a bike I'd never ridden... ) - the effect of the new jet kit with the wrong needle - was taking up too much slack in the throttle cable.  We couldn't even assemble the throttle at the grip side because it had shortened the cable so much. The sheathing didn't change length - obviously - but with the taller needle, more of the cable's  "slack" was used up at the carb end so it wasn't even long enough to assemble.

If your throttle snaps back when you let it go - it's doing it's job. The "push pull" cables aren't really that necessary on a small bike.  The return spring action is enough.  If the return spring action wasn't enough, that also would cause an issue where the bike wouldn't return to idle when you wick the throttle open and let it go - or it would stay open when you opened the throttle.  The issue you describe - idle rises when you turn the bars - is usually directly related to "free play" / slack adjustment but you don't have any on the throttle cable on a b4.

[Squishy]

All cables will shorten if you bend their sheathing.  That's expected.  Free play allows that to happen without it causing the motor to rev at the same time.  Free play also lets you hit a bump and have your right hand move without causing you to whiskey throttle it.

Well, then I'm out of luck. As I said, when I'm constant throttle at 10km/h, there is no free play, because I'm on the throttle.

I understand everything you said in the rest of your post but it it's always about slack. Slack is irrelevant in my problem. At idle my revs are not going up when I move the bars, because as you said the slack is taking care of any movement caused by the bending. However, again, it's when I'm holding steady throttle and then move the bars, where I have the problem, because there is no slack to absorb any movement caused by bending.

[stormi]

Well, then I'm out of luck. As I said, when I'm constant throttle at 10km/h, there is no free play, because I'm on the throttle.

I understand everything you said in the rest of your post but it it's always about slack. Slack is irrelevant in my problem. At idle my revs are not going up when I move the bars, because as you said the slack is taking care of any movement caused by the bending. However, again, it's when I'm holding steady throttle and then move the bars, where I have the problem, because there is no slack to absorb any movement caused by bending.

Slack is one component of the cable being too short and the thing I found easier to explain but it's all part of the same issue. This cable's still got constant tension on it regardless of the state of motion - so if something's able to jerk it, you're going to get more throttle when that condition happens. 

Assuming a properly lubricated cable and proper routing (did you download the service manual and double, triple and quadruple check it? I know you said you've tried every routing - but that one's easy to mis-read.), there isn't much to jerk that cable to pull the throttle open - other than the bars at full lock once the bike is assembled again. If the bars are making the rpms rise then there's an issue with either cable or something at one or the other end. Something is making that cable pull the throttle.
 
So, as I see it - there are 2 things you can look at: 

1.Check your return spring - I sincerely doubt this is it because you say it's accelerating from 10 -> 30kmh, which is a significant increase in speed which indicates a lot of extra throttle being pulled.  As in - not that it was being used but slowed by the brake and the brake was suddenly released because I think you'd notice if you suddenly stopped riding the rear brake. Also, there wouldn't be an audible change to the sound of the motor.  I assume there is now or you wouldn't be talking about an rpm rise.  But if you check it, you can say you did your due diligence.   Triple check that the free play adjustment at this end is correct while you're there.  Mine was always adjusted to be the loosest it could be and still caused all of these issues.

2. Take it to a bicycle mechanic - preferably one who builds bicycles.  While they may not be able to make you a legal cable, they're experts at cable routing, reducing friction inside the cable and making sure bends aren't too aggressive and proper cable length vs housings.  Better still if they also ride motorcycles but it's not necessary.  They should be able to tell you what's going on (and also properly explain why a cable has to travel "further" through a bent housing than a straight one, thus producing the effect of "shortening" or pulling it which is why I said that all of the cables you mentioned were behaving as expected. I can't effectively explain it, it's just a truth I know and have seen in action - so have you based on your description.).  The bicycle mechanic I know could troubleshoot and explain it in about 5 minutes flat.  He could also probably make the cable but not every bicycle mechanic can do that.  I'm 100% sure if I had known him when I had my b4 and took the original issue to him, he'd have questioned all sorts of things about that setup:  The fact that it comes straight off the carburetors and has to bend under the tank aggressively and is forced down by the tank causes a lot of friction.  The fact that it can't be assembled with any sort of free play and I bet even the factory routing with all of its bends. 

That would be after checking the return spring that I don't think it is.  My b4 never raced only when in motion or only when not in motion. Her 500rpm bump was if you turned the bars to full lock to the left regardless of her state of motion. What you're describing is not normal for the bike, nor is it particularly safe if it can triple your speed for "no reason".

I wouldn't say all single cable throttled bikes can't do Gymkhana because of one bike.  That's a really broad statement to infer from a single bike with a mechanical issue.

[Squishy]

Assuming a properly lubricated cable and proper routing (did you download the service manual and double, triple and quadruple check it? I know you said you've tried every routing - but that one's easy to mis-read.), there isn't much to jerk that cable to pull the throttle open - other than the bars at full lock once the bike is assembled again. If the bars are making the rpms rise then there's an issue with either cable or something at one or the other end. Something is making that cable pull the throttle.

I bought a new OEM cable, and it didn't make a difference at all.
And yes I did double-check the routing. I even tried tightening it down with tie wraps, or the complete opposite. Left side, right side, through the middle hole in the frame. I tried everything. Bot old and new OEM cable. But like I said, even if I have the cable straight through the air with the tank off or even disconnected out of the bike I can make one end move by bending it. It is not related to routing or slack.

So, as I see it - there are 2 things you can look at: 

1.Check your return spring - I sincerely doubt this is it because you say it's accelerating from 10 -> 30kmh, which is a significant increase in speed which indicates a lot of extra throttle being pulled.  As in - not that it was being used but slowed by the brake and the brake was suddenly released because I think you'd notice if you suddenly stopped riding the rear brake. Also, there wouldn't be an audible change to the sound of the motor.  I assume there is now or you wouldn't be talking about an rpm rise.  But if you check it, you can say you did your due diligence.   Triple check that the free play adjustment at this end is correct while you're there.  Mine was always adjusted to be the loosest it could be and still caused all of these issues.

Return spring is fine, throttle plates close instantly when I let go of throttle.

2. Take it to a bicycle mechanic - preferably one who builds bicycles.  While they may not be able to make you a legal cable, they're experts at cable routing, reducing friction inside the cable and making sure bends aren't too aggressive and proper cable length vs housings.  Better still if they also ride motorcycles but it's not necessary.  They should be able to tell you what's going on (and also properly explain why a cable has to travel "further" through a bent housing than a straight one, thus producing the effect of "shortening" or pulling it which is why I said that all of the cables you mentioned were behaving as expected. I can't effectively explain it, it's just a truth I know and have seen in action - so have you based on your description.).  The bicycle mechanic I know could troubleshoot and explain it in about 5 minutes flat.  He could also probably make the cable but not every bicycle mechanic can do that.  I'm 100% sure if I had known him when I had my b4 and took the original issue to him, he'd have questioned all sorts of things about that setup:  The fact that it comes straight off the carburetors and has to bend under the tank aggressively and is forced down by the tank causes a lot of friction.  The fact that it can't be assembled with any sort of free play and I bet even the factory routing with all of its bends. 

I did, in fact I did one better and went to a cable specialist, he only works on throttle/brake/clutch cables for 12 years. He changed my OEM cable into a custom one but it didn't resolve the issue, and told me it was the first time he couldn't solve a cable related problem.

I wouldn't say all single cable throttled bikes can't do Gymkhana because of one bike.  That's a really broad statement to infer from a single bike with a mechanical issue.

Well, it's probably not true, but I think most 1/2 cylinders bikes are not so sensitive on the throttle, and most other bikes have a return cable. Even the Honda CB1 has 2 cables which is closed to bandit 400 I can think of.

As you can imagine, this problem is driving me nuts. The 400 is no longer my primary bike but still.

[stormi]

I bought a new OEM cable, and it didn't make a difference at all.
And yes I did double-check the routing. I even tried tightening it down with tie wraps, or the complete opposite. Left side, right side, through the middle hole in the frame. I tried everything. Bot old and new OEM cable. But like I said, even if I have the cable straight through the air with the tank off or even disconnected out of the bike I can make one end move by bending it. It is not related to routing or slack.

Tie wraps would likely make the problem worse by increasing friction because of tiny bends. 
The cable will move if you bend the housing because physics.  I can't explain it well enough but if you can find a good bicycle forum where they are building / modding - someone will eventually explain it better than I can but the distance the cable has to travel through a bend is greater than through a straight. Therefore you're describing normal behaviour. 

What you're describing points to exactly what I'm saying:  There's a flaw in the way that cable is designed. You could buy 30 OEM cables with the same part # and they will all be as frustrating.

Return spring is fine, throttle plates close instantly when I let go of throttle.

That's what I suspected you'd find.

I did, in fact I did one better and went to a cable specialist, he only works on throttle/brake/clutch cables for 12 years. He changed my OEM cable into a custom one but it didn't resolve the issue, and told me it was the first time he couldn't solve a cable related problem.

I don't necessarily think a cable specialist is better.  He wasn't necessarily the best person for this particular job. Sometimes they're way too set in their ways or they fixate on one way being the right way and can't see the problem for what it is. When he changed the cable - did he duplicate the length difference between the cable and the housing or change it? If he duplicated the length difference, he more than likely built your custom cable with the exact same flaw.   Without knowing what he did, I'm just guessing. 

A really good bicycle builder would probably have it licked very quickly.  Bicycles are way less tolerant of cable issues because they can't use an engine to overcome anything.

Well, it's probably not true, but I think most 1/2 cylinders bikes are not so sensitive on the throttle, and most other bikes have a return cable. Even the Honda CB1 has 2 cables which is closed to bandit 400 I can think of.

As you can imagine, this problem is driving me nuts. The 400 is no longer my primary bike but still.

I'd look up some of the more traditional gymkhana bikes.  I bet you'll find more than a couple with single throttle cable setups.  There's nothing really wrong with a single cable setup when properly set up.  At this point, I believe you can't set it up properly with the equipment you have.  When I mentioned it to the other half, the response was "That damn cable! Yes, it always seemed too short!"  Neither of us misses having to fight with it every time the carbs were off.

I should also mention that my original bars were swapped for another set of what I was positive were original bars (off of another 400) and the bend was different.  Minutely different but different.

It was little issues with my b4 that lead me to finding another bike too.  I got tired of having her torn down to tweak something or having to put up with issues I didn't have on my other bikes. She made me a better mechanic but like the little kid in the Honda commercial: "Please sir, I just want to ride!"
I also notice that Honda's cable routing seems a little more sane.