I'm running a Mikuni 30mm VM series. It's not a pumper so I just layed the extra bit of cable up under the tank. That did not solve the backfire issue so many of us have. I am running the stock jets. I have also replaced the CDI, coil, and plug with "hi performance" units. That did not help either. Just for the heck of it, I'm desiginig a signal conditioner for the line from the pulse coil to the CDI.