Suzuki 2 Strokes

I have checked the spark which is good but not brilliant.
I have removed the Petcock cleaned etc
I have cleaned all the carb inside I have tried the needle at a variety of levels nothing seems to make much difference
I have checked timing/contact breakers/spark plugs all fine
The bike will rev past the redline in neutral It will Not rev past 4000 on a freeway under load, if I dip the clutch when it wont run it will redline if I want it to
With it desperately trying to maintain power at 4000 in top occasionally it slips out of gear (6th) and revs through the roof.

Just been out again new plugs no improvement...
But... I switched the lights on at the ignition switch whilst I was riding along and the bike jumped almost like something was connecting, doesn't do it when you switch the lights off when running but every time when you switch them on, isn't the headlight part of the ignition system on these?

If the electrical system is stock, then your bike doesn’t have a voltage regulator.
Instead the alternator has charging coils that always connected, and lighting coils that are only connected when the lights are on.

Does the bike run better above 4k rpm when you have the lights on?
Do you have a multimeter?

If the bike runs ok when the lights are on, then there are two fixes:
1) there is a service bulletin on increasing alternator output when the lights are off, or
2) upgrade to a modern rectifier/regulator & wire it up for maximum output

If you upgrade to a modern rectifier/regulator, than you can also upgrade to a maintenance-free or AGM battery.

Doesn't run any better with them on just jumps as you switch them on.

Check that your rectifier has a good earth connection where it bolts to the frame, this may not explain the rev question but it may explain the surging when switching.

Check that your main jets are not bigger than 112 and finally suspect your crankshaft seals.

How long have you had this bike?
Is this a new problem or are you sorting out a recently acquired bike?

These bikes have marginal electrical systems. Some of them won’t run right unless the battery is charged up.
Charge the battery & then leave it sit for a while.
Then measure the battery voltage with the bike off, and running at 2k rpm without lights, 4k rpm without lights, 2k rpm with lights & 4k rpm with lights.

Just been out and taken a radical step..I removed the Airbox working on the basis that this would determine whether it was running rich or not.
Difficult to start, vibrated a lot but more importantly revved through the 4000rpm range...admittedly at the end of the bypass the carb top rattled off and it revved its socks off even without ignition and both spark plugs fixed..I put it in 1st and stalled it that way. so it's just possible that the blighter was running rich all the time. I have it set at factory levels though with a genuine air cleaner, no way that the air cleaner (NOS) could be blocking the motor I spose?