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Discussion Starter #1
Hi All,

I have been having some issues with my 2004 660 SMC

After the last one got stolen a few years back, and with the 640 i had just not quite scratching the itch i pulled the trigger on a really mint '04 660 with only 6000 miles.

Within the first couple of rides the bike started to occasionally jerk and break up just after throttle pickup up to 1/4 throttle in low to mid rpms.
If you use more throttle it won't do this and you can normally rev through it. The bike starts easily but does occasionally die on idle. When it dies it will start up again easily and idle nicely. It sometimes also lets off massive backfires when it has a jerky moment

To try and fix this and as periodic maintenance i have:
-stripped, cleaned and rebuilt carb
-no leaks found on carb boot
-dyno tune and re-jet
-full service including air filter, spark plug, silencer re-packed,
-valve clearances just checked
-ignition timing checked

Does anyone have any suggestions as to what may be causing my issues. I'm beginning to think its ignition related.

Could a faulty Coil or condenser/ capacitior cause these issues?

Thanks in advance
 

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You've done everything I'd have done. Check the ignition lead & cap. Make sure the spark isn't jumping periodically. My sons YZ125 had a similar issue and that was the cause there. Gaffer taped the lead and cap and it fixed it until the new part was delivered.
 

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Discussion Starter #4
Thanks for the reply,
Could you tell me how to test the lead and cap?

It’s funny it’s almost like I can hear a difference in the exhaust note when the bike is about to fall into an episode of this breaking up/ jerking. If you use a lot more throttle it won’t break up like this, it tends to be just after picking up the throttle to 1/4 throttle. I haven’t noticed any power loss, once warmed up I would say the problem becomes worse

thanks
 

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Get it running, and look for a spark jumping from the HT lead to the cylinder head. If it;s difficult to see, gaffer tape the lead and cap, and see of that resolves it.
Or opt to change the ignition coil. They're cheap on ebay.
A malfuntioning TPS can also show similar symptoms. Not so cheap.
 

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Discussion Starter #6
Ok I’m with you, I’ll try that shortly and let you know what I see. Thanks for that.

I have seen these eBay coils your talking about. It’s £50 for a genuine part and £20ish for the eBay option. Do you reckon the eBay ones are any good?

So in your opinion the problem won’t lie with the capacitor/ condenser?
 

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Discussion Starter #7
Given the problem is intermittent if I could figure out how to measure and check the coils resistance figures would they necessarily read wrong as the problem is intermittent?

Thanks again Set, I’ve been getting a bit stuck here with this, electrics are not my strong point. I didn’t want to just keep throwing money at it, replace everything and not even fix the problem.
 

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Given the problem is intermittent if I could figure out how to measure and check the coils resistance figures would they necessarily read wrong as the problem is intermittent?

Thanks again Set, I’ve been getting a bit stuck here with this, electrics are not my strong point. I didn’t want to just keep throwing money at it, replace everything and not even fix the problem.
That's why I got rid of my 640. It always had it's hand in my bloody wallet. Most unreliable thing I've ever owned. Looked the nuts though.
Coil? Get an aftermarket, they're fine. Bought them for cars and bikes, and they're fine.
 

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speaking of, my 620 engine (SEM ignition) was better than the kokusan fitted on the 640 engine...

the 660 has a battery, check with a multimeter if the battery is charging with lights on (i.e. 12 < Vdc < 15Vdc) and revved slightly. same for the capacitor (careful for the polarity!!), same as for the battery.

if its only reacting to throttle from ~¼ maybe its still in the carburettor. forgot an o-ring in the FCR somewhere?
 

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Discussion Starter #10
The 660 has no battery it’s kick start only. Would checking the capacitor like you describe still be relevant? If so what figures should it read with the bike running?
It is possible something went together wrong in the carb but I doubt it. I re-assembled as per the manual, I didn’t fly by the seat of my pants like a hooligan. I used a full rebuild kit from a ktm dealer, then took it for a dyno at a local ktm centre.
Like I said the problem is intermittent so again I don’t feel like it’s carb related.
 

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Discussion Starter #11
I started the bike up and looked for any sparks from the ht lead and plug cap, couldn’t see any and nothing obviously wrong there. I haven’t had a chance to tape them up and ride the bike yet.
I’ve spied ignition coils and plug caps on eBay for £30 all in. Is that my best course of action or is there anything else I can try first?

Thanks guys
 

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my bad about the battery, had the Duke diagram in my mind which does have a battery for the cdi unit.
speaking of, there was another chap here with similar issue and wanted a battery connected for other items (charging phone or something like that).

if you can't find elswhere, send me your email address then I can send you the repair manual (LC4 1998-2005) which has the troubleshooting guide at the back.
you may want to check the wiring connectors from the generator to the R/R (yellow+white) + CDI (redblack+redwhite) + pickup (red+green) + TPS (black+yellow+blue).
also mentioned how to check the ignition (static), generator and TPS values, all can be done with a multimeter.
 

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Discussion Starter #13
I’ve dropped you a message DucATIRadeon. That would be much appreciated, I’ll get the multimeter out today and see what I find. I have been looking far and wide for those figures
 

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sent you by wetransfer due to the size (>20MB).
cheers,
Arthur
 

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Discussion Starter #15
Bit of an update, I ordered a new ignition coil and plug cap from mymotoparts. It’s a genuine ngk plug cap but the ignition coil is an aftermarket unbranded piece. Tomorrow I will get the old coil out, test it, the capacitor and plug cap, hopefully I find something. Electrics are not my strong point by any stretch.

One question I do have, the aftermarket ignition coil’s resistance figures don’t match what ktm state in the manual. Is that ok?

Ktm’s specs:
Primary (blue/white-ground) 0.425 - 0.575
Secondary (blue/white- HT Lead) 10.8K-16.2k

Aftermarket coil specs:
Primary 0.9
Secondary 13.6k

Thanks
 

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possibly it has more coils inside so higher resistance.
the secondary is inside the KTM range.
 

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Discussion Starter #17
yes it is, any idea of the implications of this? You reckon it’s fine to try it? It’s not going to fry my electrics or anything like that?
 

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shouldn't fry anything...at least not that I have ever experienced on my 620 nor my Ducati's classics with non-original electrics...

long time ago they used resistors on the primary side, something to do with shunting (don't remember, don't quote me on that). possibly the new coil has the extra resistance already built in, or it is a thing that actually effects the ignition on the kokusan units?

try it, maybe there is a difference. do let us know, I'm curious to know.
 

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Discussion Starter #19
Another update:
I removed and tested the coil and plug cap on the bike.
Here’s what I found:

Manual specs:
Primary 0.425-0.575
Secondary 10.8k-16.2k
Plug cap 3-7.5k

old coil:
Primary 0.8
Secondary 13.04k

New aftermarket coil & new cap:
Primary 0.9
Secondary 13.3k
Plug cap 4.88k

I couldn’t get a measurement on the old plug cap no matter how hard I tried.
Unfortunately the aftermarket coil would not fit, it’s the correct length from bolt hole to bolt hole but the slightly longer body fouls the mounting tabs on the frame.
So I re fitted the old coil, trimmed the ht lead and fitted the new plug cap.

Could my problem be as simple as a bad plug cap?

Any idea why my primary resistance figures don’t match the manual’s? Am I doing something wrong? Is it my old multimeter being inaccurate?

Thanks
 

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Discussion Starter #20
Oh and I did check out the capacitor as per the manual. You are supposed to hook it up to a 12v battery and test light. It should dim and go out in 0.5-2seconds. Mine was somewhere near 0.5s. It was so fast I couldn’t measure it accurately but it did dim then go out. So I assume all is ok there.
 
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