engine cutting out down track after in 3rd gear!

Update on the engine. Checked the floats and they are fine. Timing set at 34 total. Even changed plugs. No change. Still cuts out and won't pull hard from around 4700-6200 . This doesn't make since to me!! You can be going 40mph floor it and your completely sideways trying to keep it in the road. But when your actually pulling its not running right. And on the idle I worked on it for a while trying to adjust the carb to get it to idle lower. Timing set at 20 at idle I can get it to idle around 1200 and in gear just a little over 1000 but no lower. Just won't do it. Pulls around 9.5 to 10 inches vac at 1200rpm in neutral. I'm just stumped on this cutting out crap. What is going on!! I'm going to jet up the secondary side and see if that helps. I still haven't ran it with the rev limiter turned off yet either.