Author Topic: KTM 500 2-stroke Suicide Machine  (Read 9528 times)

Offline joelberg

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KTM 500 2-stroke Suicide Machine
« on: May 28, 2011, 12:14:57 pm »
Just picked up an 89 KTM 500 DXC that has apparently been revalved/resprung for MX riding for dirt cheap.  God this thing is insane.  No powervalve.  When the powerband kicks in it's a sky high wheelie in any gear at any speed.  So of course I decided to take it to the MX track the day after I bought the thing so I could thoroughly scare myself silly.  And of course I haven't ridden on an MX track in about 5 years, maybe more.  Great combo right?

http://s1134.photobucket.com/albums/m610/Joelberg/?action=view&current=2011-05-27_15-05-53_653.mp4


Here's the best video of my awesome goon riding technique.  The rest were far worse.   Gotta say that this was the wrong bike for getting back into MX riding, but I'm not crying.  I'm cruising in 4th gear in the short video because if I was in a lower gear, I'd have hit the powerband and done a nice bronco air with the bike vertical and me trying my best to keep the front end down. 

So the real reason I'm posting this thread is a plea for jetting settings.  I was hoping someone out in COGdom might have some experience with one of these widowmakers and could give me a hint where I should start jetting for low end torque with my DellOrto VHSB 38 carb.  Right now the settings are a bit lean, as the spark plug registers grey.  I'm riding between sea level and 4000 ft.  Does anyone know a good baseline I should start jetting this bike from?  I know I'd rather run fat than lean, but to be honest, this bike makes so much power I am afraid to take it past 1/2 throttle except on the asphalt!
Connie may not be the lightest, prettiest, or quickest around, but she sure gives me one heck of a ride!

Offline GF-in-CA

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Re: KTM 500 2-stroke Suicide Machine
« Reply #1 on: May 28, 2011, 05:59:50 pm »
Those things are definitely monsters, the funny thing is that KTM apparently thought it wasn't powerful enough and made a 540 in the early 90's.   :yikes:   I can't help with the jetting, but there's a guy in this forum thread

http://www.advrider.com/forums/showthread.php?t=441538

who owns one of the same vintage, you might try contacting him.  Good luck!

BTW, nice going on the tabletops!
Gary F.
1998 C10
California Central Valley

Offline Cholla

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Re: KTM 500 2-stroke Suicide Machine
« Reply #2 on: May 30, 2011, 07:15:56 pm »
Well, it's obvious it's lean, go up one size on the pilot then read the plug. Still lean go up one more size.
Beware the Black Widows...Feared throughout the land!

Offline Bmcush

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Re: KTM 500 2-stroke Suicide Machine
« Reply #3 on: May 31, 2011, 03:49:35 pm »
I'm not real familiar with KTM's but since its a two stroke that’s over twenty years old I'd make sure your leanness is NOT caused by an air leak before you begin rejetting.  When most folks begin performance mods they usually richen carb settings not lean them.  Unless the bike was jetted for higher altitude, which could be the case for 4000', you're probably looking at a leaky crank end seal or base gasket.  Have someone low pressure test the motor then go from there

Offline Cholla

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Re: KTM 500 2-stroke Suicide Machine
« Reply #4 on: May 31, 2011, 07:07:07 pm »
+1 good advice. I never think of that stuff unique to ring dings.
Beware the Black Widows...Feared throughout the land!

Offline GF-in-CA

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Re: KTM 500 2-stroke Suicide Machine
« Reply #5 on: May 31, 2011, 07:27:36 pm »
I'm not real familiar with KTM's but since its a two stroke that’s over twenty years old I'd make sure your leanness is NOT caused by an air leak before you begin rejetting.  When most folks begin performance mods they usually richen carb settings not lean them.  Unless the bike was jetted for higher altitude, which could be the case for 4000', you're probably looking at a leaky crank end seal or base gasket.  Have someone low pressure test the motor then go from there

All good advice, except to say that the one KTM I had was rich from the factory, and needed to have some carb work done beyond just jetting to get it to run right, so I can imagine a previous owner trying to lean it out and going too far.  Granted, mine had a Keihin, not a Dell'Orto, and there very well may be some case seals leaking given the age of the bike, but just wanted to put that out there.  You can try a cheap leak diagnosis by spraying some starting fluid around the base gasket and crank seals and see if it revs.  The leakdown test is still the best way to be sure, though.
Gary F.
1998 C10
California Central Valley

Offline joelberg

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Re: KTM 500 2-stroke Suicide Machine
« Reply #6 on: June 01, 2011, 08:42:44 am »
I plan on testing further and tearing the carb open tomorrow afternoon.  But the bike actually does have a new piston and ring in it.  And the cylinder wall looks good too from what I could tell shining a flashlight through the spark plug hole.

I have a feeling the pilot circuit is just plugged up.  Hopefully I won't have to tear into the bottom end.
Connie may not be the lightest, prettiest, or quickest around, but she sure gives me one heck of a ride!

Offline Cholla

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Re: KTM 500 2-stroke Suicide Machine
« Reply #7 on: June 01, 2011, 12:06:16 pm »
You'll like working on Dell'Ortos. They are stone simple.. And they work...and don't flood the cylinders with gas...

Also, go online and look up "dellorto tuning guide".
Beware the Black Widows...Feared throughout the land!