hi, is it really a flat spot, where you notice the power fade/bogs down from what it was before and after you hit 4-5k or is it more of a percieved, as in "this thing ought to have more umph than this" ? Now i've gone back and thought about it, think about throttle position and revs, is it related more to throttle, as in you back it off a fraction and its ok, back on and it goes again? or is it throttle indifferent and as soon as you hit a certain revs, bam it shits itself?
If the former, related to the carbs, if the latter, liable to be an ignition issue.
for the former, first things first if you think its bogging down, drain the carbies at least once and then put wynns carby cleaner through the engine, put in one tank at double strength, (about 2 capfulls to the tank) and then one at the normal strength and see if that makes an improvement. If it does it just means there's just gunk on the pilot jets and hopefully you've flushed it away. if not there may be more residue in there than anticipated, or there may be another issue like a carb sync required or something equally irelevant.
if it sounds electrical, it could be coils breaking down, the advance, or a few other things. Figure out the hows & why's of it shitting itself & let us know more.
p.s welcome aboard
