Please help - 50 SX Pro Junior Won't Start - KTM Forums: KTM Motorcycle Forum
 
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post #1 of 7 (permalink) Old 03-19-2014, 11:44 AM Thread Starter
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Please help - 50 SX Pro Junior Won't Start

Hello and thank you for reading this post. We have a 2002 50SX Pro junior that ran like a champ. My son rode the bike - shut it down and then it would not start. The symptom appeared to be a loss of compression or something broken in the kick start because the was ZERO resistance when you cycled the kick start. So here is what we have done:

1. Removed the case and checked the kick start assembly. Everything appeared to be in good working order and all parts are present. No obvious missing, broken, or even damaged teeth on any gears etc.

2. Removed the spark plug - as soon as we removed the plug and cycled the kick start we got resistance and the thump thump. Replaced the plug with a new one and discovered as soon as the plug was in - no resistance or thump thump - when removed - we got both.

3. Removed and replaced all top end components. Honed the cylinder, replaced all gaskets, piston, and ring (clips, bearing, etc.). Put it all back together and same thing. Pulled the case cover off again and I just don't know what is wrong. I can feel the piston move through the exhaust port when the kick start is cycled. But as described below - not every time.

So here is where I am - when the kick start is cycled - it does not rotate the crank or piston every time. About every 4th cycle I get the thump thump. Obviously there is something wrong - but I have no idea where to start. Any help would be appreciated. Thanks D
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post #2 of 7 (permalink) Old 03-19-2014, 04:28 PM
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If you put the bike into 2nd or 3rd gear will it roll freely or
do you feel the compression?

2008 KTM 950 Super Enduro R
2008 Husqvarna 610 TE

Past Rides
'14 Honda NC700X
'11 Husaberg TE 300
'06 Ducati 1000S Multistrada DS
'04 BMW 1150 RT
'03 KTM 450 EXC
'02 KTM 640 LC4e
'01 Honda XR650R
'00 KTM 520 EXC
'98 Honda XR600R
'95 KTM 620 RXC
'90 KTM 500 MX
'88 Yamaha TT600
'86 Yamaha XT 350
'84 Yamaha IT465 (STOLEN)
'83 Kawasaki KDX 450
'83 Honda CB1000 Custom
'82 Kawasaki KDX 400
'77 Yamaha DT200
'70 Honda CT70

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post #3 of 7 (permalink) Old 03-19-2014, 04:56 PM Thread Starter
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Hi Bajadog- thanks for your reply. This little bike is automatic. Normally when you push it around it behaves as though it is in neutral. Other thoughts possibly?
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post #4 of 7 (permalink) Old 03-20-2014, 12:05 PM
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Quote:
Originally Posted by blazn427 View Post
Hi Bajadog- thanks for your reply. This little bike is automatic. Normally when you push it around it behaves as though it is in neutral. Other thoughts possibly?
If the bike were not an automatic I would say that the
kick start gear compression spring is weak and not allowing
the gear to mesh with the idler gear (the one that meshes with the
clutch hub outside gear).

Let me ask a sport mini guru on another site.

2008 KTM 950 Super Enduro R
2008 Husqvarna 610 TE

Past Rides
'14 Honda NC700X
'11 Husaberg TE 300
'06 Ducati 1000S Multistrada DS
'04 BMW 1150 RT
'03 KTM 450 EXC
'02 KTM 640 LC4e
'01 Honda XR650R
'00 KTM 520 EXC
'98 Honda XR600R
'95 KTM 620 RXC
'90 KTM 500 MX
'88 Yamaha TT600
'86 Yamaha XT 350
'84 Yamaha IT465 (STOLEN)
'83 Kawasaki KDX 450
'83 Honda CB1000 Custom
'82 Kawasaki KDX 400
'77 Yamaha DT200
'70 Honda CT70

See you at Papa Fernandez!


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post #5 of 7 (permalink) Old 03-20-2014, 07:04 PM Thread Starter
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Thanks a ton!
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post #6 of 7 (permalink) Old 03-21-2014, 12:20 PM
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Location: San Diego
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Just saw your post on KTMTalk, so sounds like they helped you out.

2008 KTM 950 Super Enduro R
2008 Husqvarna 610 TE

Past Rides
'14 Honda NC700X
'11 Husaberg TE 300
'06 Ducati 1000S Multistrada DS
'04 BMW 1150 RT
'03 KTM 450 EXC
'02 KTM 640 LC4e
'01 Honda XR650R
'00 KTM 520 EXC
'98 Honda XR600R
'95 KTM 620 RXC
'90 KTM 500 MX
'88 Yamaha TT600
'86 Yamaha XT 350
'84 Yamaha IT465 (STOLEN)
'83 Kawasaki KDX 450
'83 Honda CB1000 Custom
'82 Kawasaki KDX 400
'77 Yamaha DT200
'70 Honda CT70

See you at Papa Fernandez!


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post #7 of 7 (permalink) Old 03-21-2014, 08:01 PM Thread Starter
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Bajadog - yes, thank you. For anyone interested - the likely culprit is a slipping clutch hub (likely cracked). I post a follow up if that is not the problem. Thanks again!
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