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carb balancing - how often and symptoms etc.

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trevor machine
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carb balancing - how often and symptoms etc.

Post by trevor machine on Sun 16 Apr 2017, 7:00 am

Running two 500s I get the chance to compare various aspects of the bikes. At the moment one feels much smoother than the other - so for instance, when cornering I can make very slight throttle adjustments on one bike, and it'll result in an appropriate change in speed. BUt the doing similar when riding the other bike is jerkier - and I start to wonder if I need to be using the clutch to iron out this annoying lumpiness.

The thing is, I hadn't been riding the smoother bike because it needs tyres - so after piling miles onto "Lumpy" these past couple of weeks, I rode "Smooth" yesterday. Did some 150 miles - and bloody hell it was a bit of a revelation! I had no idea how different the two bikes were, and so now I'm wondering what's causing it. I don't want to overstate it but one really is markedly smoother than the other.

So my question is simply how much of a difference carb imbalance can make to how a bike feels - particularly RE fuelling. "Lumpy" will idle well and tbh I can't really detect that much of a difference in the sound of the two bikes at idle. A more experienced ear than mine almost surely could - but I swear it's not night and day.

Ideally I should be able to provide good info of when both bikes had their carbs balanced. I'll try and suss that out later, as I do have receipts somewhere. However off the top of my head I'm thinking Smooth had its carbs done between 5-10k miles ago and Lumpy's was maybe 15-20k ago.

Obviously I've had them done on various occasions over the past few years - but can't remember really how much difference it made to the feel of the bike. I'm sort of thinking not *that* much. So now I'm wondering if there might not be some other shenanigans afoot. But what? Any suggestions, guys? Cheers.
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ceejay
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Re: carb balancing - how often and symptoms etc.

Post by ceejay on Sun 16 Apr 2017, 8:47 am

I've always felt mine was a little 'snatchy' coming on and off the throttle in turns. It was much worse when the chain and sprockets were at the end of their life, once I'd replaced them there was a big improvement. Could that be a factor?

Then not long after that I stripped and cleaned the carbs, put them back together and balanced them thinking this might improve things still but to be honest it didn't significantly help! I still feel when I go around a slow speed tight corner in second I can never smoothly open and close the throttle and feel a jolt.

I'd just accepted that's the way the bike is and I can just feather the clutch to solve it but hearing about your two bikes maybe something else is at play?
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ceejay
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Re: carb balancing - how often and symptoms etc.

Post by ceejay on Sun 16 Apr 2017, 8:50 am

Just a random thought - cush drive - I've had other bikes where deteriorating rubbers can cause a bit of this but then I've never heard a CB500 rider talk about them as an issue on this bike...
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Grarea
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Re: carb balancing - how often and symptoms etc.

Post by Grarea on Sun 16 Apr 2017, 8:55 am

I am far from an expert, especially as I have only had this since last august.
Mine was pretty lumpy.
Quite hard to explain isn't it?
Each time I have done something it has improved it slightly.
The main one I found was I think it was blowing at the header end.
I discovered all sorts there. Sorting that made quite a difference.
Changing the air filter made a difference as well.
I have just used sainsburys fuel instead of my normal Shell optiwhatever and it is a bit lumpier again. Still not as bad as it was before sorting out the blowing.
I am wondering if there is something else myself.
Perhaps the better fuel is covering up for something. Not sure.
I balanced the carbs before thinking that was the issue, but it didn't make a lot of difference.

Now it seems that I possibly have a clutch issue. It seems to be binding.
Am wondering if that makes any difference.

But I also suspect I need to replace chain and sprockets.
I also have a bit of a grumble when i have the power on that sounds a bit bearing like (or maybe chain and sprockets, not sure)
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trevor machine
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Re: carb balancing - how often and symptoms etc.

Post by trevor machine on Sun 16 Apr 2017, 10:54 am

@ceejay wrote:I've always felt mine was a little 'snatchy' coming on and off the throttle in turns. It was much worse when the chain and sprockets were at the end of their life, once I'd replaced them there was a big improvement. Could that be a factor?

Then not long after that I stripped and cleaned the carbs, put them back together and balanced them thinking this might improve things still but to be honest it didn't significantly help! I still feel when I go around a slow speed tight corner in second I can never smoothly open and close the throttle and feel a jolt.

I'd just accepted that's the way the bike is and I can just feather the clutch to solve it but hearing about your two bikes maybe something else is at play?

Good call on chain and sprockets - I can't see how, when worn and/or poorly maintained, these *wouldn't* contribute to lack of smoothness. So yeah - definitely. However front sprocket is less than a month old, rear and chain are good, and the whole lot are always clean and EP90'd. I might neglect other stuff - like e.g. bike's cosmetic cleanliness, but chain/sprox and all pivot points are always clean and lube'd. 

"I still feel when I go around a slow speed tight corner in second I can never smoothly open and close the throttle and feel a jolt."

Exactly! Just lately I've started taking hairpins and tight turns in one gear higher than usual, and the bike can do it. You kind of think it can't, that it might bog down half way through, and then the corner will really get cocked up as you proceed to change down halfway through. Lol nightmare. But in fact, providing you not going up hill, etc., the bike does seem to have a tiny bit of torque in reserve, that comes in very handy for this kind of thing. However, and having said that, I do think the bike prefers a slightly more assertive attitude - which is to say, in general, the lower of two possible gears approaching and riding through a given corner. It *is* a little bit fussy sometimes, compared to bigger engined bikes with torque everywhere. 

But, bracketing all of that, that issue you pinpointed seems to be a fairly typical trait of a bike with a twin configuration. My W650 did the same thing - but not so pronouncedly, because it was in a softer state of tune, and was probably more easy-going in general.

I'm starting to wonder if I might not take to an il4, with all the whizzy innate smoothness that comes with it. Hornet, perhaps. Or - gulp - cbf600. The times that I've ridden them, I did think yes okay, lost some character - but gained some refinement.
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trevor machine
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Re: carb balancing - how often and symptoms etc.

Post by trevor machine on Sun 16 Apr 2017, 10:59 am

@Grarea wrote:I am far from an expert, especially as I have only had this since last august.
Mine was pretty lumpy.
Quite hard to explain isn't it?
Each time I have done something it has improved it slightly.
The main one I found was I think it was blowing at the header end.
I discovered all sorts there. Sorting that made quite a difference.
Changing the air filter made a difference as well.
I have just used sainsburys fuel instead of my normal Shell optiwhatever and it is a bit lumpier again. Still not as bad as it was before sorting out the blowing.
I am wondering if there is something else myself.
Perhaps the better fuel is covering up for something. Not sure.
I balanced the carbs before thinking that was the issue, but it didn't make a lot of difference.

Now it seems that I possibly have a clutch issue. It seems to be binding.
Am wondering if that makes any difference.

But I also suspect I need to replace chain and sprockets.
I also have a bit of a grumble when i have the power on that sounds a bit bearing like (or maybe chain and sprockets, not sure)

Chain and sprockets can make quite a lot of noise, to be honest. I was really surprised just how much - and actually only found out the other day. There was a 2000s CBF250 in for service and inspection - I had a little go of it around the compound, and couldn't believe how rattly and horrible the whole bike sounded. Which was a bit of a shock because, cosmetically, it didn't look three bad. New chain and sprockets did a lot to quieten the bloody awful sound it made, though.
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ceejay
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Re: carb balancing - how often and symptoms etc.

Post by ceejay on Sun 16 Apr 2017, 5:07 pm

But, bracketing all of that, that issue you pinpointed seems to be a fairly typical trait of a bike with a twin configuration. My W650 did the same thing - but not so pronouncedly, because it was in a softer state of tune, and was probably more easy-going in general. 

but are you saying one of your CB500s doesn't experience this? I can live with my bike as it is if I knew it was normal but if I know it's possible to have a smoother throttle response when coming on off the power then I can try to get mine there somehow. I will have a go and taking turns in a higher gear though as you say.
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trevor machine
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Re: carb balancing - how often and symptoms etc.

Post by trevor machine on Sun 16 Apr 2017, 7:18 pm

I'm definitely and emphatically saying one is markedly smoother than the other. It could be an age thing though - it could all be down to wear and tear. You can tell a difference between the two bikes as soon as you've kicked your leg over it. One is firm and sort of solid - the other sinks down and feels like a comfy chair. So in some ways I think what I'm experiencing is merely the mechanical side of this. One young, one old - as it were. Whether the old can be rejuvenated somewhat by a carb synchronising remains to be seen. I honestly don't think there's a whole lot else can be done to the bike though, because it had air filter, valve check and what-not last year - so doesn't want for much, even though it will hit 60k in the next month or two.
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trevor machine
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Re: carb balancing - how often and symptoms etc.

Post by trevor machine on Sun 16 Apr 2017, 7:33 pm

@ceejay wrote: I will have a go and taking turns in a higher gear though as you say.

Yes - the downside of this is that it's more of a faff to power out of the corner, because of course, you're in a higher gear at lower revs. So maybe this kind of approach is better for your average everyday commute rather than a more spirited ride. Hmmm. Regardless, it does make me wonder how these lads who race them get on with this jerkiness mid-corner malarky, cos it is a bit disconcerting when it happens.

The only thing I can think is that they're masters of smoothness, and/or they "ride around" the issue by setting the throttle in advance and "just" chucking the bike in to the turn.

However, the problem for us mere mortals is achieving what is sometimes apparently referred to as a "maintenance throttle." This means cornering in such a way that the bike's speed does not change throughout the entire curvature of the bend. Which in practice means that you have to twist the throttle ever so slightly in order to compensate for the loss of speed incurred as the bike deviates from a straight line. Inevitably this loss of speed is usually felt mid-corner, and to combat it we give the throttle a little helpful twist, that probably amounts to not much more than a millimetre - and yet the bike's reaction can seem quite disproportionate to this input, and becomes somewhat unsettled as a result. 

Why does an otherwise very obedient and tractable bike have this slightly ill-behaved streak? Probably just cos it's a twin. But how these blokes that race them deal with it, I'd love to know - because I can imagine at technical tracks like Cadwell it can become a bit wearing at times. As said, I suppose this is just one of the various things that makes them bloody good riders! ; - )
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hh_12345
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Re: carb balancing - how often and symptoms etc.

Post by hh_12345 on Sun 16 Apr 2017, 10:02 pm

@Grarea wrote:I am far from an expert, especially as I have only had this since last august.
Mine was pretty lumpy.

Mine is even worse - it is not consistent.

There are days it is smooth, quiet and powerful. And there are days it's noisy, lumpy and slow. I do improve anything I can though, but I have stopped to really care as it is a bit tiring sometimes.
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Jameshambleton
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Re: carb balancing - how often and symptoms etc.

Post by Jameshambleton on Sun 16 Apr 2017, 10:23 pm

Mines quiet lumpy from cold at times but nothing much. I've alway found getting the tension on the chain on the cb5 really hard to get correct, any other bike I can do it fine. 

The chain as mentioned plays a massive part in the scratchiness of the throttle depending on your riding style, ideally you always want to go into a corner with a little bit of power on, then the chain won't have any slack to take up causing the jalt so it'll be smooth... Not that I even do this my self that often.

The low down torque has often massively helped me out, as has the +2 size rear sprocket. Then again with my old engine (before I blew it up) taking it for a reasonable blast at 8k+ rpm made the engine run a lot smoother after doing constant speed motorway road works at 4k rpm in 6th.
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ceejay
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Re: carb balancing - how often and symptoms etc.

Post by ceejay on Sun 16 Apr 2017, 11:32 pm

After having my carbs apart and seeing how smooth the cable operated butterfly valves are, where you have very precise and infinite movement (which is very different to what feels like is happening when experiencing this 'lumpiness') my instinct is that it is not throttle or carb related... so that leaves somewhere between front sprocket and tyre.. although I am no expert and could be completely wrong!

James raises good points about the chain and it's true in an ideal world you'd want to keep the throttle on and smoothly accelerate out of a corner where my bike probably wouldn't have a problem... however in a typical UK scenario when you are going around a badly pot holed off camber roundabout with one eye on drivers playing with their phones and the other on the three slippery looking man hole covers you are trying hard to avoid the throttle tends to open and close somewhat causing the bike to jolt and my confidence to be knocked.

Next time I have my rear wheel off I might check for play in the cush rubbers and maybe wrap them in some old inner tube so they are packed tighter into their housings as an experiment. Like others have mentioned though this is likely to be one of those problems that is the result of a combination of many factors... or even just a characteristic of the machine and I should just use the clutch or improve my cornering to smooth it out.. 

If only I am ever available to go to one of the meets someone can have a go on my bike and tell me 'normal' or 'not normal'!
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Melitos
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Re: carb balancing - how often and symptoms etc.

Post by Melitos on Mon 17 Apr 2017, 10:56 am

Hi,

My 2 eurocents on the subject:
The vacuum operated pistons on carbs might cause all kind of strange symptoms if they do not slide smoothly. The pistons are plastic and might scratch easily if air filter is not up to it's duties.

BR,
Antti
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ANDYC
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Re: carb balancing - how often and symptoms etc.

Post by ANDYC on Mon 17 Apr 2017, 1:55 pm

Two engines will never be exactly the same in the real world.
Balancing the carbs is really the icing on the cake so to speak. Unless everything else is spot on it's a waste of time. 
Valve clearances any leaks either intake or exhaust side. Spark plugs and leads would all make a difference. 
One thing to note is that as our steeds of choice have reached such an age now many parts are 'past their best ' for want of a better description. The small filter box that is linked to the carbs to keep crud out of the vacuum chambers contains a sponge that has a habit of falling apart and ending up in the very place it's meant to protect. This can restrict free movement of the slides which doesn't help a smooth throttle operation.
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trevor machine
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Re: carb balancing - how often and symptoms etc.

Post by trevor machine on Mon 17 Apr 2017, 10:07 pm

@hh_12345 wrote:

@Grarea wrote:I am far from an expert, especially as I have only had this since last august.
Mine was pretty lumpy.



Mine is even worse - it is not consistent.

There are days it is smooth, quiet and powerful. And there are days it's noisy, lumpy and slow. I do improve anything I can though, but I have stopped to really care as it is a bit tiring sometimes.

Okay, after spending all day on "Lumpy" (see above), I have to basically agree with this comment - there are smooth days, and there days that are not so smooth. Basically, Lumpy wasn't that lumpy at all - and I started to wonder if I'd imagined the whole thing.

Bloody weird. And in any case, even when Lumpy wasn't so smooth, it didn't feel bad, wrong or difficult to ride. Just, well, different (than the other bike aka "Smooth").

Neutral scratch Neutral scratch

All of which is good, really. Today, at least, I don't feel like I've got a bike that's a bit wayward and which has annoying traits I have to "ride around." So I'm not complaining, as such - just scratching my head a bit. I suppose the problem probably lies with me the rider, rather than the bike - for the most part. I enjoyed pretty much every moment of riding it for the six or so hours (albeit broken up into two hourly chunks separated by almost the same amount of time OFF the bike). There was no mid-corner lurching, no "missing a beat" here and there, and no awkward throttle opening moments worth mentioning. So I could only conclude it the fault lay on the organic rather than mechanical side of things. I.e. me the rider.

Hmmm.
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ceejay
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Re: carb balancing - how often and symptoms etc.

Post by ceejay on Mon 17 Apr 2017, 11:06 pm

- and I started to wonder if I'd imagined the whole thing. 

haha I do exactly the same thing - some days my bike feels smoother than others but I've concluded that the bike is staying consistent and it's my senses that are varying from day to day!
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trevor machine
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Re: carb balancing - how often and symptoms etc.

Post by trevor machine on Tue 18 Apr 2017, 7:00 am

My senses - and, in my case, more than that, my ability. I reckon. ; - )
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trevor machine
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Re: carb balancing - how often and symptoms etc.

Post by trevor machine on Tue 18 Apr 2017, 7:03 am

@ANDYC wrote:The small filter box that is linked to the carbs to keep crud out of the vacuum chambers contains a sponge that has a habit of falling apart and ending up in the very place it's meant to protect.



*gulp*

Shocked Sad

I'm getting a bit paranoid now Andy! Laughing
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ceejay
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Re: carb balancing - how often and symptoms etc.

Post by ceejay on Tue 18 Apr 2017, 12:41 pm

Mine carbs had those bits of sponge inside when I opened them up, however, surprisingly, cleaning them out didn't noticeably change the feel of the bike, I can see how they could though and it's probably down the luck where they end up resting in the carbs!

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wornsprokets
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Re: carb balancing - how often and symptoms etc.

Post by wornsprokets on Tue 18 Apr 2017, 1:05 pm

I took carbs off my cb 500s  few weeks ago.. notice air mixing jets were different positions left one was in further than right one(these are ones that can be seen  at bottom of carbs when on bike) anyone settings for those...?
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ANDYC
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Re: carb balancing - how often and symptoms etc.

Post by ANDYC on Tue 18 Apr 2017, 9:01 pm

Std setting is 2.5 turns out.
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eternally_troubled
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Re: carb balancing - how often and symptoms etc.

Post by eternally_troubled on Tue 25 Apr 2017, 10:00 pm

I can certainly agree that chain slack/wear can make a big difference to smoothness.

After I snapped my throttle opening cable (while overtaking!), I found that once I'd replaced the cable the whole bike felt smoother because my throttle cable was gliding smoothly and was properly adjusted - so if you don't know how old the throttle cable is then I'd have a go at replacing/inspecting that.  Also worth going over the cable adjustment and seeing what happens (easy to do!).

I'd also bet that cush-drive rubbers could be coming to the end of their life - even if they haven't started falling apart I'd bet that the rubber doesn't have the same properties now that it once had 20 years ago... sadly a new on is £60 quid from Lings (luckily a non-Honda one is £30 from wemoto)...

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