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Author Topic: KTM 640 Adv idling.  (Read 999 times)

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Offline missinglink

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KTM 640 Adv idling.
« on: September 05, 2012, 09:17:43 am »
On 25 000km my 640 decided not to idle anymore. Removed carb, cleaned it and reset float. Problem persists. Will idle OK but then suddenly will drop,stutter and die. If standing still you need to keep reffs up otherwise it dies.Sprayed carbcleaner, poured injecter cleaner in petrol. No luck.

Also starting to "backfire" when you lat go off throttle or down shift.

Could it be idle jet needs replacing? Need to try and sort this out myself as $$$ is in very short supply!!!

« Last Edit: September 05, 2012, 12:41:56 pm by missinglink »
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Offline Metaljockey

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Re: KTM 640 Adv idling.
« Reply #1 on: September 05, 2012, 10:33:30 am »
When revving it to keep it going, any black smoke from the exhaust?

Offline missinglink

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Re: KTM 640 Adv idling.
« Reply #2 on: September 05, 2012, 12:39:48 pm »
No black smoke(made sure now-even when you rev it up no smoke).  Forgot to mention that it also started "backfiring" every time you take hand off throttle/down shift.
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Offline WabbitKiLR

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Re: KTM 640 Adv idling.
« Reply #3 on: September 06, 2012, 07:58:20 am »
Soos in die ander thread gepost...

Ig

I had the same problem with the KLR earlier on in the year. I ended up stripping the whole carb and putting it back together. This somehow solved the problem so I am assuming it was a blocked jet or something. I thought as I have it off I might as well clean the entire thing.

It runs beautifully now...much better :thumleft:

I say remove the carb and strip it down to the bare bits (best have a service manual nearby if you feel you need one to reassemble the thing), you might find a lot of gunk in there. Rinse the bowl and the jets and so in petrol. I know of this carb cleaner that you get, but I don't know if your carb has a diaphragm of rubber like mine - I have heard some cleaners can attack the rubbery bits. Also visually check the jets for blockage and if possible blow them out with compressed air (be careful, you don't want to go chasing a flying bouncing jet across the garage). One more thing regarding the backfire - check your exhaust headers and the section where the midpipe joins up with the end pipe for leaks. My KLR has a bit of a leak halfway between the silencer and the header and I get a lot of popping on deceleration.

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Offline Rascal

Re: KTM 640 Adv idling.
« Reply #4 on: September 06, 2012, 08:19:30 am »
Where is the needle on idle  1000/1500 ??

What mods have you done:
is the slide drilled?
bigger jets exct?
 

Offline Metaljockey

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Re: KTM 640 Adv idling.
« Reply #5 on: September 06, 2012, 08:37:41 am »
No black smoke(made sure now-even when you rev it up no smoke).  Forgot to mention that it also started "backfiring" every time you take hand off throttle/down shift.

No idling when hot, backfiring and black smoke normally points to a stuck choke slide. You have two out of three, so it might not be the problem. However, it is easy enough to check and clean without removing the carb. The slide on the Mikuni BST40 is prone to get gunked up and then to stick open.

Another possibility that is easy to eliminate, is air leakage between the carb and the head because of not seating lekker or clamps having been fitted wrong.

Offline lecap

Re: KTM 640 Adv idling.
« Reply #6 on: September 06, 2012, 09:25:09 am »
Disassemble, clean thoroughly, assemble.

You need a bit of an understanding of what sits where and does exactly what when working on a carb. To make sure you clean where it counts and don't loose tiny washers & o-rings you might not even know they exist.

Spraying carb cleaner into the velocity stack as the tin suggests will not help. Neither does pouring stuff into the petrol tank.
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Offline Dux

Re: KTM 640 Adv idling.
« Reply #7 on: September 06, 2012, 09:29:26 am »
Something I have picked up on quite a few 640's is that the plastic housing where the choke cable enters the carburettor tends to break , if this is the case it can suck air and create rough idling . If that is a problem contact me , I have those units in stock .
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Offline missinglink

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Re: KTM 640 Adv idling.
« Reply #8 on: September 06, 2012, 11:57:51 am »
Where is the needle on idle  1000/1500 ??

What mods have you done:
is the slide drilled?
bigger jets exct?


1500 on idling with no mods done.
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Offline Rascal

Re: KTM 640 Adv idling.
« Reply #9 on: September 06, 2012, 12:07:10 pm »
Something I have picked up on quite a few 640's is that the plastic housing where the choke cable enters the carburettor tends to break , if this is the case it can suck air and create rough idling . If that is a problem contact me , I have those units in stock .

not a bad idea. those break just looking at it.

If its stock, then I'm not sure what could the cause could be other that dirty carb, rubber seal leakage or jetting. If modded the idling will have to be set to +- 1700 rpm.


 

Offline missinglink

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Re: KTM 640 Adv idling.
« Reply #10 on: September 10, 2012, 08:15:33 pm »
Took carb of today and cleaned it. Assembled it again(making sure all is there) Fitted all pipes with new clamps and checked plastic housing on carb(choke)-start up and no f@rking change. Idles k@k! Seems like I will have to take it in to someone with much more knowledge than me. And there goes the $$$. :'(
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Offline WabbitKiLR

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Re: KTM 640 Adv idling.
« Reply #11 on: September 10, 2012, 08:19:43 pm »
Ig

How clean is your fuel tank?

Water in a fuel tank can cause just as much nonsense sometimes. See if you can drain the tank to the best of your ability and see what gunk comes out.

If you can, take the tank off, slosh some fuel around in it and decant it into a bucket or something. See if you can see any debris or water in it.
 

Offline Brolox

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Re: KTM 640 Adv idling.
« Reply #12 on: September 10, 2012, 08:28:30 pm »
I had more or less the same issue on my 690 - turned out to be the coil???
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Offline missinglink

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Re: KTM 640 Adv idling.
« Reply #13 on: September 10, 2012, 08:30:35 pm »
Ig

How clean is your fuel tank?

Water in a fuel tank can cause just as much nonsense sometimes. See if you can drain the tank to the best of your ability and see what gunk comes out.

If you can, take the tank off, slosh some fuel around in it and decant it into a bucket or something. See if you can see any debris or water in it.

Nee tank is skoon,het laas naweek met baie steun en vloek hom geflush. ;D
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Offline missinglink

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Re: KTM 640 Adv idling.
« Reply #14 on: September 10, 2012, 08:31:25 pm »
I had more or less the same issue on my 690 - turned out to be the coil???

Might try that,didn't even think of that. :thumleft:
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Offline missinglink

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Re: KTM 640 Adv idling.
« Reply #15 on: September 10, 2012, 08:32:28 pm »
Thanx all for all the advice and help so far,appreciate it! :thumleft: :3some:
When someone told me I lived in a fantasy land I nearly fell of my unicorn.