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Discussion Starter #1
Have a misfire on my 250 exc. At mid to high revs it misfires and sounds like a rev limiter coming in. Can't rev through it - need to roll off then on again to stop it.
The carb has been stripped and cleaned, the breathers are clear. Fuel tank tap and internal filter is spotless. The valve clearances have been set by the dealer. I've replaced the coil, ht lead, plug, suppressor cap and air filter for all brand new. Plug gap is correctly set at 0.6mm. I took off an after market petrol cap breather thinking it might be airlocked. The right hand kill switch is disconnected as this was suggested as a fault from a previous thread but no help.
I'm thinking of changing the CDI next but its a bit pricey to just take a flyer on it.

Any ideas? Please help if you know anything - it's a pain! Ta, Mick
 

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Discussion Starter #3
All I know is that its clean. The carbs been done and is spotless but not sure if the jets have been swapped out for a non standard size by prev owner
 

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Discussion Starter #5
the cap has been changed - i changed it along with the new coil and ht lead and new plug...
 

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Even though it may not be to blame i would check the jetting, including the needle and needle clip position, just for elimination if nothing else and it only takes 10 minutes if that.
 

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You may have aproblem with your stator coil(s). Remove ignition cover in lhs of bike and see if there is any crap in there or anything obvious. You can also check winding resistances but you will need the KTM manual to verify what the values should be.
 

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Discussion Starter #10
Fergus- gonna swap the cdi unit tomorrow from a mate's bike that is running fine. if that cures it all's well. if not then i'm gonna change the primary pick-up coil. Mort- would the accelerator pump give these misfire symptoms at mid to high revs?
 

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Discussion Starter #11
Ok - swapped the stator coils today for the one from my mates bike which is working perfectly. This didn't cure it. I'm gonna fit a new set of primary pick-up coils when they arrive from ktm as these were not tried from my mates bike (didn't want to knacker the gasket on his bike - the rubber plug lies beneath it.) Swapped his ignition coil, ht lead, plug and suppressor cap even all of those parts on mine are new. Still got the problem. Removed the carb, adjusted the float height to let in a bit more juice thinking it might be fuel starvation - no joy - problem still here. Only thing I havn't changed is the cdi and the primary pick-up coil.
His cdi unit will not fit mine. His has a throttle position sensor whereas mine does not. I've ordered one from the U.S. for a monster £168 jeeeeesuz H. Keeeerist!!! I'm positive it's electrical. Hope this isn't needed and it's the primary pick-up but never mind - it'll be up for sale on ebay if it's not necessary.
 

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it doesnt matter if your mates cdi has a throttle ps , u can still sub it and give it a try , i know because ive done it with mine , i have the same bike as u and subbed my mates 04 450 cdi to check mine out and his worked perfect on mine, its a chunk of cash to part with ukless u no for certain
 
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