I have posted this before with no real help. I have a 686, 12.1 piston, stage 2/springs, full yosh with K&n filter, port and polish. It came with 175 170 jets. I am at 6200 feet. In nebraska where i got it, it ran awsome with this set-up at 2500 feet. I brought it back to 6200 feet where i live and it ran like crap. Missing when floored at highier rpm. I raced a z400 stock and it beat me. I changed it to 170 165 and its a little better but still stumbles some so i'm thinking 165 160 but this seemes like a real low number. Please help me for i'm lost on what to do.

 

Are you using the air box lid? Are those mikuni jets?

 

yes their mikuni jets and my lid is half cut off.

 

i would try 165 160, 160 155 seem a little to lean. you may not think so but 4000 ft increase in elevation can make a hugh difference with jetting. just play with it you will get it straight.

 

I agree that seems like to small of main jets. Can you take the lid off and try it or does it hold your filter?

 

The lid holds the filter. I placed 160 165 on it and it made a big difference. I raced my wifes z400 and where she used to beat me i beat her by 10 to 20 bikes. It doenst seem to stumble when floored but it does stumble when 3/4 throttle. So im not sure if i should go down one more main jet or now play with the needle. If i'm right moving the clip down is going richier and up makes it leaner? So i'm think i need to raise my clip one to lean the 3/4? Or should i try going down one more jet. Please any advice would be apprieated.

 

I had the same prollem...
I would drop the needle down a notch(raise the clip)
and see what that does.....

 

i would think that there is someone on here with a 686 at about the same elevation. So if your close to 6200 please let me know your jetting.

 

I am not using the stock carbs, but this might help. I was at 148/150 @ 1,000ft and 140/145 @ 7500ft elevation. But the FCR's do not seem to be as tempermental as the stockers. My sister's semi-stock raptor is running 180/185 @ 1,000 ft and 160/165 @ 7500ft elevation with stock carbs. Hope this helps

 

Raptor660fam, Are they dynojet numbers or are those mikuni jets. So you were running 145 150 at 7500 with a 686 kit. If this is the case i don't feel so bad about 160 165. thanks, anyone else?