You just have to rev it higher when starting off in first gear with the A/C on. Very low revs with the A/C on = very little power. I typically take off from ~1200-1500 rpms in first. With the A/C on I'll take it up to 2 grand, sometimes more if I'm starting up a hill.

 

A light weight crank pully, ala Vishnu-Perrin will help a bit.
A light weight flywheel would totally cure it, and improve all gears at all times. Do a clutch at the same time and your golden. I'm in love with a Jun FW and Clutch masters stage 3 clutch combo these days.

k2

 

turn your ac off and roll down your windows

 

I recently pulled my AC off. I don't use it anyway. I have a custom 480 AC, 4 windows rolled down at 80mph

k2

 

A FREE mod that can be used to increase boost is the popular 3/16" mod, or the "pulled hose" mod. Both will help you boost faster, and make more boost to boot. I did a variation of the "pulled hose" mod by replacing the factory restrictor with a 1/8"x1/8"x1/8" T, and this definitely helped out. Some people have mentioned problems with PTFB (part-throttle, full boost), but I have driven with this setup for about a week now, and have never seen anything other than vacuum at part throttle (unless I am on my way to WOT of course). Also, if you don't already have one, get a boost gauge. Anything to mess with the boost settings is unsafe without one. Good luck.
________
Honda Cb450Dx-K

 

I was purpose built for hot weather.