KLE500 sputtering and stalling at motorway speeds

[Vracktal]

For the past couple of months, i've had an annoying fault with my 1993 KLE500. Riding around town and on windy roads it's generally okay, but getting on a motorway and riding it at around 70mph for more than 20 or so miles causes it to start spluttering and coughing.

Weirdly, when it does this, I can "cure" the spluttering temporarily by opening the throttle more, it'll magically run clear and fine again as I accelerate, but once I stop accelerating it'll go back to spluttering and coughing, with the power cutting out and in sporadically while it splutters.

Another thing is, if I pull off the motorway, it will either die completely as I close the throttle, or come close to dying, but after a few seconds I can fire it up and it'll run perfectly fine again, as long as I stay off motorways.

This also seems to happen more often on an emptying tank (less than half full) than on a full one. Although, even on a full tank I can make the problem happen by taking it up to around 100mph, which will immediately make the symptoms occur.

So far, the possible problems I can think of it being are:

1) Vapour lock?
2) Dirty carbs?
3) Failing pick-up coil?

Anyone got any ideas how I can nail down exactly what's causing this and fix it?
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2007 BMW R1200R: On road
2009 BMW G650X Challenge: On road
1975 Norton Commando 850: Off road, awaiting recommissioning

[P.]

What is your fuel taps set up? vacuum or completely gravity fed?

[Vracktal]

I believe it's vacuum fed, but on the tap I have the option to turn it to "PRI" which lets the fuel flow freely (tested with the tank off, fuel runs at a good rate)

Turning it to "PRI" when it's sputtering has no noticeable effect on the problem though. Should also mention I have checked the fuel filter and line to the carb, it's an inline filter type and doesn't inhibit fuel flow as far as I can tell. (tested this with the tank off too, when set to pri fuel runs through the filter and hose to where the carbs would be if they were connected)
____________________
2007 BMW R1200R: On road
2009 BMW G650X Challenge: On road
1975 Norton Commando 850: Off road, awaiting recommissioning

[Ariel Badger]

Make sure that your tank is venting properly.
____________________
Bikers make great organ donors, get 115 on your licence today.

[weasley]

I know it's summer now (pfffffft!!) but this sounds like classic carb icing. Water in the fuel tank maybe? Unseasonable cold weather?

Or maybe float height?
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[dansp1]

Sounds like carb icing, lots of Kawasakis used to suffer with it, does the bike have heater pipes on the carbs? if it does check they are still flowing coolant.
There are fuel additives that will stop it so you can find out for sure that that is what is occurring

[dansp1]

must type faster

[Nexus Icon]

It hit 22 degrees here today. No one is getting carb icing.

More likely vapour lock. As Ariel suggested, check the vent in the filler is clear.

Does it hissssssssss when you open the filler cap?
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Greetings from Shitsville!

[dansp1]

Carb icing is affected by humidity as well as temperature and we have had enough cold and damp days over the last couple of months i would have thought.

https://en.wikipedia.org/wiki/Carburetor_icing

If it were a blocked tank vent it wouldn't cure itself after a couple of seconds as quoted.

[_Iain_]

Chuck a can of pro fst in it & see where that gets you. Its an additive that prevents carb icing, so it'll eliminate that.
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[Vracktal]

[Vracktal]

-UPDATE-

Okay, so ordered some FST Pro, while I was waiting for it to arrive I decided to take the bike to the shops - only it refused to start at all. Engine turned over, but wouldn't catch.

Swore a lot, stripped off all my bike gear and prepared to walk, only just before I gave up, decided to give it one last go (about five minutes after I last tried) and it started fine. No trouble at all.

After that it ran fine. Took it to the shops and back, even made a 35 mile round trip on motorways to collect a tyre, cruising at 70mph with no issue whatsoever.

Hopefully the FST Pro will arrive tomorrow, so will throw a 2% dilution into the tank and fill it with premium juice just as a bonus. If that doesn't work and the problem comes back will strip the carbs down, clean everything with a toothbrush and a microscope, take them to be professionally balanced and set up, and see if that cures it.
____________________
2007 BMW R1200R: On road
2009 BMW G650X Challenge: On road
1975 Norton Commando 850: Off road, awaiting recommissioning

[P.]

What colour is your spark.

Also, have you taken the tank off and removed the fuel tap..

[cb1rocket]

Classic symptom my bros was doing. Tank vent was blocked. Splutter at motorway speeds and dies. Leave for a few minutes and it will restart ok
____________________
Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[Fizzer Thou]

The easiest way to test for a blocked tank breather is to support the tank off the bike and to drain petrol into a measuring container.Time the amount of fuel that it takes to get to a measured level and see if it slows after a few minutes.Then do the same test with the filler cap open.

I suspect that the CV carb slides are sticking,especially as this only seems to be happening once the slides will have opened ie. above 4-5,000 rpm.Ensure that the diaphragms are seated correctly and that the very small 'O' rings that go between the carb top and the body of the carb are not split.Clean the slides with WD40 and the inside of the carb with cleaner.Fuel residue can build up after some time and cause the slide to stick.Then,once the carb has cooled,the spring will push the slide back to its seated position.

Carbs are easily cleaned and balanced.It does not need to be done 'professionally'.
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'

[unitynotsocri...]

i suspect your diaphram rubber/worn carb.

I would suspect far more carb wear on a big single cylinder engine than a multi,reasoning (not my best skill) that far more air/petrol has to travel through for a larger cyclinder volume.
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nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[Vracktal]

Time to update this thread

So far, i've swapped the carbs for a pair that I know work fine, are clean and in balance, as well as cleaning all the pipes including overflow pipe, breather pipe and main fuel pipe. I also swapped the fuel tap for one I know to be good. I've changed the ignition coils and checked the airbox and air filter. I also filled it up with BP Ultimate + a 1.5% FST mix.

And it still does it. Not only that, but now sometimes at startup from cold it does it as well. I'll start it up, and it'll be sluggish to rev and splutter, and won't rev past 6k. If I ride it, it'll behave like the original symptoms for a while, and then after about a quarter of a mile or so it'll suddenly stutter a bit and run completely fine. Once it's done this it'll behave as long as I keep under 70mph.

I made a video showing the difference between running from cold, and running after a ten minute ride. The exhaust note is different, and sounds laboured, and won't rev properly until i've taken it out for a ride.

https://youtu.be/gY6OpsXYfJQ
____________________
2007 BMW R1200R: On road
2009 BMW G650X Challenge: On road
1975 Norton Commando 850: Off road, awaiting recommissioning

[cb1rocket]

Is there a fuel pump on this?
____________________
Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[Irn-Bru]

[Vracktal]

After several beers pondering A thought has come to me:

I wonder if I could set it on fire and claim off insurance?

When I've put the tank back on i've never checked if the fuel was feeding directly from the tank to the carbs, maybe if the fuel pipe was getting a ubend in it like a toilet that could explain why it runs rough for a while, until i take it out for a ride and the engine being under load creates enough vaccuum to overcome this.

And then when i'm on the motorway maybe the engines trying to draw down fuel so fast that the ubend is enough to interrupt the fuel flow makin it stutter at speed?
____________________
2007 BMW R1200R: On road
2009 BMW G650X Challenge: On road
1975 Norton Commando 850: Off road, awaiting recommissioning

[cb1rocket]

try running with a separate makeshift tank, we def now know its fuel related
____________________
Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[unitynotsocri...]

you could try and rev test it , instead of at high speed motorway stuff you could rev it in 1 st and 2nd and see if the little fcker wants to cough and splurt at the same rev range .

Considering you've changed the carb would nt this prove its ignition or valve gear related ? (but only if the trapped pipe doesnt cure it.)
____________________
nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[Vracktal]

Resurrecting this thread because a month later and the problem is still there. Took the bike out for a ride, when I started out I noticed the throttle was lagging slightly, i'd wind on and it would take about a second for the engine to respond. This went away after about two or three minutes, so I kept going. After about four or so miles of 50-60mph riding the bike started spluttering and coughing as usual, as if it was running out of petrol. Pulled over, opened the tank cap while it was idling just to see if it was something breather related, but it just shut down alltogether. After that, it refused to start. I tried opening the choke full, and it would just about idle raggedly if I did that, but attempting to open the throttle at all would cause it to shut off.

In the end I had to push it home (well, most of the way, it's still about a mile away after I gave in to exhaustion and abandoned it.)

I really am at my wits end with this bike. Some days it runs without issue, although it feels slightly underpowered at all times, and other days it'll just be a complete shit.

The list of things checked so far=

Carbs- Cleaned thoroughly, balanced, checked that nothing is sticking open. Currently it's on the stock jetting, but it was running fine with these for years before the problems began so I can't think what would cause a change.

Spark plugs- Gap is correct, no fouling on the plugs

Fuel lines- Cleaned all of them, checked for kinks (none) and made sure there were no hose leaks.

Fuel tap- Checked flow was good

Fuel tank breather- Cleaned out with pipe cleaner.

CDi unit- Swapped over for a good spare I have from my other KLE.

Ignition coils- Swapped over for two nearly new ones from my other KLE, and double checked with a multimeter from cold, and again after running up to temp for ten minutes.

H/T Leads- Switched for clean, almost new ones from my other KLE.

Wiring- Checked for any breaks or fraying.

Also have been filling up with 98 and running a 1.5% FST mix, problem remains.



Out of desperation I might rig a transparent plastic bottle fuel tank as suggested earlier and see if I can replicate the fault, problem is it's so intermittent I can never pin it down when I want to observe it.
____________________
2007 BMW R1200R: On road
2009 BMW G650X Challenge: On road
1975 Norton Commando 850: Off road, awaiting recommissioning

[unitynotsocri...]

The only thing in the list of hard work that may be at fault is when you said you checked the air filter . Sometimes its best changing the filter and seeing ,?
____________________
nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[Blau Zedong]

Trigger coil breaking down?
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18:54:48 Rob Fzs: jews don't give away stuff for free

18:54:59 Rob Fzs: unless its their clothes/ hair/ golden teeth