Im at 3.5 rear and 3 front 850' elevation. It does help, but why do you have them uneven?

 

Apparently your rear Carb does not need as much fuel enrichment as your front carb does. Your rear carb main jet is probably larger than your front and if your engine is happy, idles, runs, & starts good, you have tuned your bike to it's specific needs. Every bikes needs are different based a lot of factors and your settings/jetting will change with added mods, temp, elevation.[img]i/expressions/face-icon-small-cool.gif[/img]

TuffEnuff

 

From what I understand, the reason is that the front cylinder is set to run leaner than the rear due to the fact that it cools slightly better than the back one. Not sure but the difference in exhaust pipe length may also have something to do with it.

 

589 is right... rear is hotter and the stock jet is 4 bigger than the front #138 vs #142

Common to twins (and many multi cyliders). On my Valkyrie 6 banger, the rear two took a larger jet when rejetting and I only shimmed them and added an extra to the back two to get uniform plug reads.... one each front four, two each rear two... my old Suzuki Intruder 1500 was the same way, had to back out the rear air screw half a turn extry..

 

The reason is the unequal exhaust length. The rear pipe is short and straight, therefore it scavenges better and creates a leaner condition.

 

Interesting, thanks. I guess on my inline 4 FZ1, the middle carbs are different than the outsides, makes sense.