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Idle issues and single cylinder when wet

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louis_sutton
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Idle issues and single cylinder when wet

Post by louis_sutton on Fri 19 Feb 2016, 12:18 am

Evening all,

I chased down some electrical problems on my 2000 CB500S a while ago - which included a replacement of the HT leads.  And a change of sparks to iridium about a year ago.  All hunky dory. Fitted a stubby can after the stock rotted through.

For a while I've had an issue at idle where the revs will drop down sporadically and unpredictably, going from about 1500 (currently set a touch high) to just under 1000, but not stalling.  More an irritation than anything else, but I figured out during the week that it doesn't seem to happen with the lights off, so I'm currently assuming that the battery might just be losing it's edge (although I ran it through an optimate overnight and it didn't change things, so it may well be new battery time, or indeed something entirely different).

In addition, my neutral light is hit and miss when the engine warms up - which may well be the spliced earth wires, although I do need to clean both the clutch switch, the neutral switch and the sidestand switch, just to make sure.  Irksome rather than a problem, to be honest.

But here's the real problem - the bike got drenched yesterday.  Out in the rain all day, proper soaking wet.  And when I started it for the commute home, only ran on one pot.  I figured out during the ride that if I kept the revs well up even whilst stationary, the second pot would come back to life.  I can't help but think electrics at this stage and am wondering if the increased revs meant the bike was generating enough power to overcome whatever was interrupting the spark in the second cylinder - which could be the battery being a bit duff, the reg/rec playing up, or a few other things.  If anyone's got any opinions, I'd welcome them, as I'm just sorting a plan of attack at the weekend to try and resolve things.

At the weekend I've got all the switches and contacts to clean, and will include the earth points in that.
Balance the carbs, and make sure the idle screw is correct.
Check the plugs, and deploy multimeter throughout (including reg/rec).  I'd like to clean the carbs properly (maybe with a rebuild), but that will probably be useful to wait a bit on, as I'll buy an ultrasonic cleaner for the carbs on my non-running CX, and use that for the CB carbs first.

I'm tempted to buy another battery because I don't know how old the current one is (it'll also get a check and a test under load at the weekend).  I'm also tempted by a new reg/rec (any recommendations for decent ones would be appreciated), and sparks if they look ropey when I get them out (shouldn't do though).

If I can get that a bit more sorted, I'm wiring in some heated grips so will try and do a photo by photo instruct as it'll be going in with a relay, linked into the rear brake light switch for a switched live, with power off the solenoid, all neatly under the RHS panel, which hopefully might help someone in the future.

Phew - that was a bit longer than I anticipated.  As I'm far too conscious that there are loads of people here with much more expertise than I, any thoughts/comments/guidance would be greatly appreciated!

Cheers
Louis
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eternally_troubled
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Re: Idle issues and single cylinder when wet

Post by eternally_troubled on Fri 19 Feb 2016, 12:28 pm

Well, from what you've written, it sounds like you have a sensible plan of attack. Charging and load-testing the battery sounds like a good idea.

Do you have another battery (from another bike or even a car) you can substitute for the suspect one on the bike? Even if it's off a 'borrowed' car or bike battery from a friend/relative it might help. You can then run the bike (when stationary, at least) and see if the 'one-cylinder' problem goes away.

I suspect that if the bike can manage to pass the charging voltage test that you said you were going to do then it's *probably* not the battery (if your battery was reallyshot then it will drag the result of the charging voltage test down).

The main snag with running one cylider is that if the *working* one then fails you are a bit stuck... Wink
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louis_sutton
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Re: Idle issues and single cylinder when wet

Post by louis_sutton on Sat 20 Feb 2016, 2:27 pm

Well the battery is at 12.7 with bike off and no lights. Drops to 11.4 with lights on, and about the same under load, up to 14.5 at over 3k revs.

Onward, in that case... Better start spraying bits with water!
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Re: Idle issues and single cylinder when wet

Post by eternally_troubled on Sat 20 Feb 2016, 6:34 pm

@louis_sutton wrote:Well the battery is at 12.7 with bike off and no lights. Drops to 11.4 with lights on, and about the same under load, up to 14.5 at over 3k revs.

Onward, in that case... Better start spraying bits with water!

That gives the impressions that your charging system and battery are fine... it could just be a dodgy/corroded connection and the water is the 'final straw'.
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louis_sutton
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Re: Idle issues and single cylinder when wet

Post by louis_sutton on Mon 22 Feb 2016, 12:35 pm

You may well be right. Still confused that it runs like rubbish with the lights on, and seems fine without though!

That said, I do need to rerun all the tests with a properly hot engine. Got distracted by orders from she who must be obeyed...
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Re: Idle issues and single cylinder when wet

Post by eternally_troubled on Mon 22 Feb 2016, 12:45 pm

@louis_sutton wrote:You may well be right. Still confused that it runs like rubbish with the lights on, and seems fine without though!

That said, I do need to rerun all the tests with a properly hot engine. Got distracted by orders from she who must be obeyed...

That does sound a bit odd.

I've had issues with the charging on my bike that *I* thought were a real problem but actually turned out just to be journey-related: my previously commute was about 6 miles/25 mins through town - stop/start, accelerating away from lights, not much above 30/40 mph for any amount of time. I found out that my battery wasn't being charged sufficiently by my journey (essentially the revs weren't high enough for long enough) if I had the headlight on all the time.

I fixed the problem by using sidelights-only when it was light and reserving the headlight for use in darkness.

So, it *could* be that your charging system is fine but you've knackered your battery by, essentially, not commuting far enough or fast enough.

Of course, this is all irrelevant if you commute 70 miles every morning on the motorway... ;)
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louis_sutton
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Re: Idle issues and single cylinder when wet

Post by louis_sutton on Mon 22 Feb 2016, 1:35 pm

Hmm. I'd not thought of that. My commute is 30 miles, takes about ninety minutes. Ten miles at motorway speeds, and the rest through the middle of London.

I'll have to consider that, intending to re check whilst the engine is hot tonight if I can.

You're right though, it d seem to be just the headlight, the side light doesn't do it.
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Re: Idle issues and single cylinder when wet

Post by eternally_troubled on Mon 22 Feb 2016, 2:14 pm

@louis_sutton wrote:Hmm. I'd not thought of that. My commute is 30 miles, takes about ninety minutes. Ten miles at motorway speeds, and the rest through the middle of London.

That really should be enough time/distance... it could "just" be that your battery is past it?

The previous measurements (resistance, voltages etc) shouldn't really change when the bike is hot, so it's probably worth doing just to (try and) rule that out.
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louis_sutton
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Re: Idle issues and single cylinder when wet

Post by louis_sutton on Mon 22 Feb 2016, 4:27 pm

I am wondering if it's a borderline battery. It would actually be a relief if checking it hot gave different results, just so I had a target. I'd certainly rather be tinkering with it to fix it than working today!
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Alvi
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Re: Idle issues and single cylinder when wet

Post by Alvi on Tue 23 Feb 2016, 9:35 pm

Re: idle speed dropping when h/l on, had a problem on one of my wife's bikes a while back - a Virago 535. It started misfiring when accelerating, but only when the h/l was on. I changed the reg/rec & tried another battery with no luck, so she just used it without lights for a while. Turned out the rear ht lead had a soldered joint that was breaking down. Probably a P.O had swapped a dodgy rear coil for a front coil & joined on a bit of ht lead to extend it. I never worked out why having the light on would affect it! If you have recently changed the ht leads, could there be a poor joint somewhere?
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Re: Idle issues and single cylinder when wet

Post by eternally_troubled on Wed 24 Feb 2016, 12:23 pm

@Alvi wrote:Re: idle speed dropping when h/l on, had a problem on one of my wife's bikes a while back - a Virago 535. It started misfiring when accelerating, but only when the h/l was on. I changed the reg/rec & tried another battery with no luck, so she just used it without lights for a while. Turned out the rear ht lead had a soldered joint that was breaking down. Probably a P.O had swapped a dodgy rear coil for a front coil & joined on a bit of ht lead to extend it. I never worked out why having the light on would affect it! If you have recently changed the ht leads, could there be a poor joint somewhere?

I reckon this:

The bad solder joint increased the resistance in the HT lead, but not enough to stop it working completely.

When you switch the headlight on the voltage across the low-voltage part of the coil will decrease (as the battery voltage sags with the additional load of the headlight) - this slightly reduces the voltage that causes the spark on the high-voltage side which normally wouldn't be a problem, however, because of the increased resistance (due to the bad HT lead joint) there isn't enough HT voltage to cause a proper spark at the plug.
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Alvi
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Re: Idle issues and single cylinder when wet

Post by Alvi on Wed 24 Feb 2016, 9:38 pm

@eternally_troubled wrote:



@Alvi wrote:Re: idle speed dropping when h/l on, had a problem on one of my wife's bikes a while back - a Virago 535. It started misfiring when accelerating, but only when the h/l was on. I changed the reg/rec & tried another battery with no luck, so she just used it without lights for a while. Turned out the rear ht lead had a soldered joint that was breaking down. Probably a P.O had swapped a dodgy rear coil for a front coil & joined on a bit of ht lead to extend it. I never worked out why having the light on would affect it! If you have recently changed the ht leads, could there be a poor joint somewhere?





I reckon this:

The bad solder joint increased the resistance in the HT lead, but not enough to stop it working completely.

When you switch the headlight on the voltage across the low-voltage part of the coil will decrease (as the battery voltage sags with the additional load of the headlight) - this slightly reduces the voltage that causes the spark on the high-voltage side which normally wouldn't be a problem, however, because of the increased resistance (due to the bad HT lead joint) there isn't enough HT voltage to cause a proper spark at the plug.


I was thinking something along those lines. I replaced the dodgy ht lead by fitting the correct coil with it's longer lead, but had charging problems for a while longer despite swapping the cdi again. I eventually replaced the alternator 7 that sorted it.

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