bogging down

I have a 1976 kz900 with stock 26mm carbs with a #115 main and a #15 pilot. It has either the 1015cc or 1035cc kit in it. It bogs down when i first takeoff from a stop(just in neutral it revs up great but as soon as its is under a load it bogs). what jets should be used i was going to try a 17.5 pilot jet and see what it is like.

If it bogs as you roll on the throttle from idle I would check the fuel levels in the carbs and maybe adjust needle height.

it sounds to me that your needle heights are to rich try the middle position also look at your gearing it might be to high how long have you ridden the bike and have you done anything different to it. let's start with that first give us a list of what is on this bike [air filters ,pipe, cam's and whatever else you can think of or find out. it kind of sounds like you must have just got this bike.

had it a couple months actually(just got tired of messing with it). ive tried different needle heights, adjusting the mixture screw, setting float levels, cleaning the jets . it has individual k&n's(just cleaned and oiled), a vance & hines 4 into 1(unmolested that has the baffle), stock cams (so i was told), dyna coils and ngk sparkplugs and caps. I always run 93 octane gas and use 10w 40 oil

it sounds like your main jets are close and your stock pilots would work does it idle alright and return to idle alright by itself,one other question does it accelerate well in the other gears.

The main jet is stock size for a 76 KZ900. The stock pilot jet should be a #17.5. Do you have the stock airbox on this bike?

If not already done, would assure strong spark, correct ignition timing and advancer function, and check/adjust valve clearances and floatbowl fuel level. All before addressing carbs. Because even perfect carbs won't compensate for failures in the non-carb components.

Good Luck!