sputter / backfire

I managed to get the brakes sorted out. Thanks for all the help.

On to a new problem:

1971 Commando 850 with a mikuni carb. stutters and backfires after it warms up from about 1/4 throttle to 3/4. Im running a boyer and the ignition is set at 28 degress BTDC. The plugs look good.

Most of my experience is with amals and points so i am totally lost.

Please help.

#1 put new plugs in. Gap at at least .030 with a Boyer and 6 volt coils.
#2 make sure the plug wires are known to be good.If you don't know replace.
#3 Boyer's should be timed at 31 not 28 check with a strobe at 5000 RPM
#4 check the wires at the Boyer pick up plate they break inside the covering.
#5 Check your petcocks for flow and your tank for rust if metal and melting if it's fiberglass as most 71's have.
The list goes on....