Pre ignition = lean mixture?

4 replies to this topic
  • Taipan

Posted November 04, 2003 - 03:39 AM


Hi All,
My new to me '92 XR600 has some jetting issues. As I get to know the bike I'm noticing more things. The biggest concern is it pinks under load if the throttle is opened quickly. This is a sign of a lean condition right? What would be my next move, up a size on the MJ?
Any advice will be gratefully recieved.

  • AzMtnThumper

Posted November 04, 2003 - 05:43 AM


At what RPM (and throttle position)is the pinging occuring? Assuming you have the proper octane level of fuel and the correct heat range of spark plug: Right off idle might mean pilot (are you able to set the air screw properly?), mid-throttle could mean needle, half to wide open could be the main jet. My bike pings at about 1/3 throttle under light load once in a while. I'm thinking I should raise the needle one position (kinda of a pain in the butt) and see how it does. I've tried octane booster to the 91 octane Unocal 76 gas I usually run but have had inconsistent results.

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  • Taipan

Posted November 04, 2003 - 08:03 AM


Its in the top half of the throttle range.
I thought needle adjustment was very easy on these? I was going to alter mine later? I was told, losen carb, pull round 45 degrees. Remove carb top. Undo arm and remove. Lift out slide and remove/alter needle. Reassemble?
It sounded very straightforward........

  • JR650

Posted November 04, 2003 - 04:56 PM


one thing to check, pull the head, see how much carbon is in there, carbon deposits form hot spots and contribute to detonation. Detonation is when 2 flame fronts start, ie, something other than the plug is lighting your gas too, or the flamefront is begin disturbed and separated by something in the chamber (carbon) when the flame fronts hit it explodes. a hot chamber will detonate easier, lean can make for a hot condition. Try better gas, leaded runs cooler. Try jetting up like you said, and i really would pull the head and see if there is any carbon in there. have fun, JR

  • AzMtnThumper

Posted November 05, 2003 - 07:26 AM


"It sounded very straightforward........" LOL yeah, it's not that bad , just watch those small screws on top of the slide. I had a little trouble getting the threads to start because I kept dropping the screws down into the slide :D.


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