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Author Topic: KTM 640 LC4 Engine won't rev above idle  (Read 691 times)

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Offline Panjo

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KTM 640 LC4 Engine won't rev above idle
« on: May 12, 2011, 07:57:37 pm »
Allo Dawgs, SO, Last week I took my LC4 for a ride, to loskop and back, with no issues. A week later, a chap comes round to test drive her and she gets halfway round the block and the engine dies. The prospective buyer says No thanks and leaves. Now, she starts easily enough, but idles very unevenly and as soon as you open the throttle to give it a blip, she dies. It feels like, when you twist the throttle gently that it's almost like an electronic type of rev imiter effect in place. The only thing that happened to the bike in the last week was it got a wash. Any ideas? FYI-The side stand switch was done long time ago.

Thanks, Panjo!
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Offline N[]vA

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #1 on: May 12, 2011, 08:07:57 pm »
Allo Dawgs, SO, Last week I took my LC4 for a ride, to loskop and back, with no issues. A week later, a chap comes round to test drive her and she gets halfway round the block and the engine dies. The prospective buyer says No thanks and leaves. Now, she starts easily enough, but idles very unevenly and as soon as you open the throttle to give it a blip, she dies. It feels like, when you twist the throttle gently that it's almost like an electronic type of rev imiter effect in place. The only thing that happened to the bike in the last week was it got a wash. Any ideas? FYI-The side stand switch was done long time ago.

Thanks, Panjo!
Yep, check that the rubber boot connecting your air box to your carb hasn't got a gap in it some place, also check that your fuel isn't contaminated
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Offline Runner

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #2 on: May 12, 2011, 08:24:00 pm »
The circlip on the needle has come off
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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #3 on: May 12, 2011, 08:24:45 pm »
The circlip on the needle has come off

Makes maximum sense 8) if your 1150 does the same the TPS connector is loose 8)
« Last Edit: May 12, 2011, 08:33:37 pm by Welsh »
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Offline Sprocketbek

Re: KTM 640 LC4 Engine won't rev above idle
« Reply #4 on: May 12, 2011, 08:36:33 pm »
Wild guess: Could be something to do with the throttle sensor. It's the flat black thing on the side of the carb.
The wires are apparently black and yellow respectively.

Check for a broken or chafed wire.

From the manual:

Checking the throttle sensor (from model 2003 on)
NOTE: the adjustment must be made in a mounted condition with the
cable connected and the ignition switched on.
Use a digital multimeter to measure the voltage between the black
and yellow cables at the connector 3 (CDI).
! CAUTION !
SINCE YOU MUST MEASURE WITH THE CONNECTOR ATTACHED, MAKE SURE TO
CAREFULLY PUSH THE MEASURING TIPS ON THE MULTIMETER THROUGH THE SEALING
FROM THE CABLE SIDE AND NOT TO DAMAGE ANY PART OF THE CONNECTOR.
Reading with closed throttle (neutral position): 0.88 +/- 0,075 volts
Slowly open the throttle valve with the throttle grip, the measured
voltage should increase uniformly up to the full load reading.
Reading with fully opened throttle grip (full throttle position):
3,88 +/- 0,1 volts.
Adjusting the throttle sensor
Loosen the screw on the throttle sensor 4 and turn the throttle
sensor until you reach the reading for the neutral position.
Tighten the screw on the throttle sensor.
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Offline Sprocketbek

Re: KTM 640 LC4 Engine won't rev above idle
« Reply #5 on: May 12, 2011, 10:14:49 pm »
The circlip on the needle has come off

I didn't see Runner's answer before I posted mine but I gave it some more thought.
Agree it's something like that most likely.
On the 640 the TPS probably just advances the ignition timing.
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Offline Poffmuis

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #6 on: May 13, 2011, 12:16:08 pm »
blocked main jet also possible. something that snuck past the filter?
 

Offline Panjo

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #7 on: May 15, 2011, 04:01:39 pm »
Just a quick update. Have not had a chance yet too take the bike apart and have a proper look as I'm in the middle of Unisa Exams, buit I started her just now and on the centre stand I was able to quickly put her in to gear and accelerate. I let her idle for a whle and then came back and noticed the problem had not gone away.
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Offline LouisXander

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #8 on: May 15, 2011, 06:21:14 pm »
Circlip in the motor?? Eina pappie, check ASAP!!!
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Offline Panjo

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #9 on: May 28, 2011, 05:24:02 pm »
Turns out it was only a dirty jet Yay!
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Offline Poffmuis

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #10 on: May 30, 2011, 09:56:05 am »
Yeah, classic symptoms. Hope you replaced the fuel filter.
 

Offline spider pigs dad

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Re: KTM 640 LC4 Engine won't rev above idle
« Reply #11 on: May 30, 2011, 01:40:46 pm »
the cir clip is on the inside of the slide so it is almost imposable for it to get into the engine . The blocked mainjet is the first place I would check .
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