No High RPM's

Just got my '82 750 twin running and idleing. I am running into a problem when I go to rev the engine in neutral. It will go to around 3500-4500 rpm's and then drop off. Like it isn't getting air or something. Anyone come into that problem? Would it be a vacuum issue or something?

Kinda stumped at this point. Maybe the bike won't let you rev to redline in neutral?

Please shoot me some ideas....

If it's missing or cutting out at the high rpms, I'd suspect the timing advance first. I'm not familiar with the 750 twin but I assume it has a mechanical advance on the points plate, much like my CB550. I sold my KZ400 in '83 or so and I can't remember exactly how the timing advance worked on that bike.

It may also be a fuel issue, i.e. the carbs can deliver enough to get you to 4500, but no more.

Check the timing advancer (springs and weights behind the points) and make sure the points cam rotates by turning it with your fingers. It should turn one direction only, and snap back when you let go.
3500 rpms is where it's supposed to get full advance.