as mentioned on ktmtalk some '08 EXC-R bikes had CDI issues. I did as well on my 530 and running the bike on the soft map made the surging/misfiring magically disappear. however I don't know if this was the case on all the bikes that encountered this problem. it's hard to diagnose this issue as the symptoms can be linked to so many other things. logic dictates most people will figure it's the jetting. others will suspect the ignition, mainly the plug or plug cap. even others just figure they hit the limiter.

CDI is the last thing you would think about, but the only way you can rule it out is to get a hold of a more recent model year unit and fit it on the bike, then run it in the same condition the problem usually pops up. easier said then done I know... if I lived closer I'd just give you one, got an '09 CDI collecting dust after I got rid of my 530 little over 2 years ago. it solved the issue in my case.

another thing you could check is the TPS adjustment, but that's another longshot guess.

 

He borrowed a known good CDI from a friend of his and is going to test that today. That way we can know if it is definitely the CDI. We also disconnected the TPS, I suggested the TPS because of it fixing a similar issue on my WR450. I'll pay to ship that CDI if you really want to get rid of it.

 

So we switched CDI's from his to a known working '09 CDI and no dice. It still breaks up under load in the top of 5th and 6th.

 

There have been issues with fuel vents on some of the KTM's. Check the vent, and if only a half tank or lower of fuel, just ride with the cap off.

 

It doesn't feel like lack of fuel, it feels like hitting the rev limiter, but instead of pinging it shuts the power off. But at 7k rpm I wouldn't think that was anywhere near the limiter.

We will try the no cap thing and see how it works. The only other thing we can think is that the coil may be bad.

 

coil breaking down under load ? .... try good known coil ..., same with sparkplug cap ,
good luck

 

New development! We took it to a local dealer friend and had him run it, at 7000 RPM it breaks up, but at 7700 RPM it clears up and acts normal. He says it is something electrical, so now we need to test connections for a fault.

 

It’s my humble opinion that it’s jetting…..Meaning, it’s wrong. WHat did your dad just do? Did he go up on the jetting? It sounds rich.

 

It’s my humble opinion that it’s jetting…..Meaning, it’s wrong. What did your dad just do? Did he go up on the jetting? It sounds rich.

 

He ordered a 185 main but never installed it. After 2 miss orders we finally got a proper plug cap :banghead: but it got rid of the break up in 5th, but 6th is still breaking up. We are going to rewrap the coil and see if that solves it.

 

Update: As of 4/27/13 the problem still persists. One caviat is that when we test a new configuration we get one good run, the bike pulls hard all the way up to rev limiter in 1-6. Then when we pull around to do another run back, the problem shows up again. Starts in 5th breaking up feeling like the spark is skipping.

We have sheathed the coil wires to make sure there was no electrical noise causing spark signal interuption, changed everything in the electrical system. We put a different carbuerator that was jetted properly and the problem still persisted. We are out of things to try...

Now he is making sure there are no air leaks. I still think it is an electrical issue, like a bad ground so we are going to go through the electrical system to make sure everything is tight.

 

By any chance you got this figured out after 10 years? H