WOT stumble

[DaveJ]

Mark,
Thanks for your reply. I was in my local Yamaha/KTM dealer (the only bike dealer in town) looking at a KTM mini for my son and started talking about my WOT problem. He also suggested trying to go leaner. Monday I am going to pick up a few more main jets and try it out. In the other jetting thread it was mentioned that 178/180 is right in the ballpark for these bikes yet you had good luck with a 160 in a 300cc bike.....I am getting a little confused as to what is going to be too lean or too rich.
BTW, switching to the bigger 180 main improved the midrange throttle but still had the WOT stumble. I also installed my new FMF silencer/spark arrestor (which sounds just as quiet as the stocker) and the stumble is still there so definately not related to that.
I live at about 500' above sea level if that helps any.

 

[DaveJ]

Just like to say thanks to everyone for their input and how nice it is to have this forum.
I finally picked up some smaller main jets today. They didn't have a 175 so I picked up a 172 and 168. I put the 172 in and the stumble almost disappeared, still had a bit of a bog at WOT and when I let off slightly it surged a bit. I put the 168 in and raised the needle from the 2nd to the 3rd clip, stumble is now gone and the bike pulls nice and smooth all through the throttle range without any hesitation. I'm going to pick up a new plug next week when I'm off work and do a proper plug chop.
I do find it a bit strange how far off everyones jetting is, seat of the pants riding tells me this is the ticket yet some here have almost cringed at the thought of running such a lean main. I'm sure once the temperature and humidity come I'll have to adjust it a bit as it's only 5C here now.
Thanks again.