Bike: 1975 R90/6 Cam:336 (6 degree advanced been can type) Carbs: 38mm Dellortos (R90S jetting except for richer #65 idle jet) Pistons/Cylinders: (Siebenrock 9.5:1 1000cc pistons with Nikasil Barrels) New Heads are rebuilt with later rocker gear and dual plugging. Ignition is a crank mounted Omega. timing set at 3 degrees advance with 28 degrees full advance. I just put 300 miles on the bike since making all the modifications. For the fist 150 miles of breaking in the bike ran amazingly well with lots of smooth torque throughout the range. Since then I've noticed a drop in power over 4500 rpm and cutting out at full throttle. To try and remedy the problem I...... I replaced the floats and adjusted the bowl levels. Adjusted and equalized the throttle pumps. Balanced the carbs tried richer and leaner main jets tried advancing and retarding final advance New plugs Compression is 140 psi on both sides. Leakdown test shows only 2-3% leakage, none on valves. I'm sure if I keep tweeking it I'll eventually find what's going on, but right now I want to ride. Any ideas?