Performance Modifications

After an entire year of my 1977 RD400 running reliably and strong I decided to screw it all up. Performance modifications. You can put them off for only so long before that gnawing itch needs to be scratched. Don’t fight the inevitable, bend like a reed in the wind.

I got a good deal on some DG Expansion Chambers and started tuning. I found scraps of useful information on various message boards and forums and gathered some jets. I started way too big 220 main jet and 25 pilot. I kept the pilot, swapped out with the largest mains I could scavenge that day 135 and dropped the clip one position on my needle to compensate for the potentially lean mains. That got me around for a couple days and burned some reasonably tan/gray plugs until I scored a set of 165 mains and reset the needle to stock. This has improved things dramatically but theres a crappy flat range from 1/4 – 3/4 throttle that must be fixed.

I’m studying this valuable bit of Mikuni Carb Theory for the answers. I scored some Banshee Manifolds with the crossover fittings and plan to remove the stock air box and mount individual air filters. I’ll bump the mains back up to 220 and tune according to plug color and performance. Wash, rinse, repeat.