Going about 80mph on the highway and then flat lined( cut off ). Went to the side to start and got backfire. Towed the bike and had spark plugs replaced, started fine but with the backfire and something strange. Open throttle and it was jumping from 0 rpms to 2000rpms and kept jumping back and fourth. So I took the carbs off and cleaned them piece by piece in the ultrasonic cleaner. Second, took the top ends off to clean any carbon on the pistons, heads and valves. Put all back together and was doing the same thing. Idles and starts fine but when I open the throttle its still jumping from 0-2000 rpms with never going over at full throttle. Also at full throttle I feel the air and small amounts of fuel being pushed backwards. Did a pressure test and got 120 psi readings from both pistons. Pre mixing 30:1 ratio and at idle smokes just a bit. When the throttle is fully open and it's jumping , sounds like there's no build up of air. Haven't checked the crank seals yet or can it be electrical. Please help.