I reckon you'll be a good few thousand feet up then? 100km in what direction from Pretoria? Still on the fat ass shelf that it sits on?

you need it dyno testing.. but for me, I would be sure that the air filter is a good quality and in good condition.

Are you a big lad? Are you racing with bigger bikes? NC30s are not that fast in the general scheme of things and to be fair, once you are past 100mph it does not go as fast as it did.

What sprockets have you got on there too?

not really ,i took another nc30 on the freeway and it left me so far behind .........
after that he told me that he wasn`t even punching it so what gives ?
as for the sprockets- front 15/40 rear-.

Main jets only start operating over 8000 revs so if the problem is present below these revs then it's something else.

It sounds similar to symptoms of when the speedo is disconnected (or wire cut) and it cuts the spark to 2 cylinders when running over 5000 rpm.

Check for spark from one front and one rear plug (one at a time) over 5000 revs to eliminate this as the cause.

SilverSurfer wrote:i`m in the north west province 100km from Pretoria, so what ur saying is that 106 should be fine for where i am? or should i go ahead and change them to STD jets?

Check if you have 30 or 35 carbs first

nc30 carbs, and speedo is working fine as far as i know ,i`ll check the spark when i have time , and when i punch it the rev`s don`t want to go higher than 8500 but when reving in neutral it goes to the red line so i think you might be onto something .

SilverSurfer wrote:nc30 carbs, and speedo is working fine as far as i know ,i`ll check the spark when i have time , and when i punch it the rev`s don`t want to go higher than 8500 but when reving in neutral it goes to the red line so i think you might be onto something .

dont rev it over 10,000 in neutral.

There is no load on the engien so there is an increased likelyhood of somethign going bang, while it doesnt often happen, an old motor, unknown problems it just adds to the risk.

Is your airbox all there? Flap / Snorkel / Air filter (stock)?

Many people mess around trying to improve it but it often ruins the fuelling.

air intake is dead standard

I would take a guess that the main jets are too small and it's running far too lean.

It would certainly be worth putting some 118/120 jets in and seeing how it goes.