Sounds like a missfire

Its running, had to drop to a 76 jet but only getting 22mph

 

Would it now be down to rollers, belt and springs?

 

Could be the rollers yeah

 

Got 5g in at the moment would you go heavier or lighter? Also got 2 polini prelod springs for the clutch plate

 

***UPDATE***

After some work over the weekend i have now managed to hit 60mph with the original exhaust fitter (still with restricted pipe) ehich is a good thing.

Today taking the bike on a run in the countryside all seems fine on full revs (9k ish) then for some reason loss of power after around 1-2min only manage to get power back by decelerating then accelerating again and it seems to carry on like that un till i pulled over for a minute or two then seems fine for 1-2min again.
I was thinking this could be lack of fuel? but thought best to ask you guys.

 

Quite right in your assessment.
The carbs running out of fuel at that speed.
I'm assuming you still have the standard carb on it?

 

Yeah still the standard 17.5mm one.
Im guessing with the 70kit on it i should be around 20-21mm?

 

Actually, the 17.5 should be ok. Maybe a little float adjustment is required, could be too low shutting off the supply early.

 

How do you do that Steve? Only just sort of possibly maybe got my head around jetting

 

There should be a metal tab on the float where the needle attaches. Bend it carefully to raise the float height. That means that more fuel will be in the float bowl before the float needle shuts off the supply.

 

Sounds good, will give that a try in the morning, thanks Steve

 

Had a look today and doesnt seem to be a tab, the needle sits on a plastic lug on the float

 

Thats awkward then.
You could try lookng for an alternative float first but might be hard to find, try NRP carbs they might have one, but I suppose ultimately a carb upgrade will be needed.
However, saying that, 60mph (indicated) on a 70cc runner is perfectly acceptable, in fact it would make some owners jealous.