i got an nrg mc3 03 plate with a 12mm carb and i put a leo vince tt pipe on it ,a mallossi variator with belt and to start with it had a 60 main jet in and was slow and got told its running weak so got an 82 main jet off my mate and one of those bigger air boxes from a older nrg(says high performance airbox on it) and it still runs slow (splutters ocaisionally) could it be too big will a stage 6 open filter make it run better and wot the best jet size for it thanks for any advice(seems to rev better without airbox but put it bak on without road testing it incase it damaged it)

simon, January 2010

if its running better without the airbox then theres no doubt at all that its running too rich.tuning a 2 stroke can be very difficult and jetting is a hit and miss thing unless you have it on good authority that a certain jet will work with other non standard components.i personally have a set of micro jet drill that go from 0.2 mm up to 1.6mm and i simply make the jet slightly bigger until its right of course i know roughly where to start from experience.if i were you i would try a smaller jet a 70 or 75 would be a good start from there you can move the circlip on the throttle slide needle up or down to distinguish which side of the rich/lean scale you are on moving the circlip towards the pointed end of the needle will make it richer and away from the pointed end leaner.you could try moving it now with your 82 jet to the non pointeed end to see if it improves it slightly but as i said no airbox and it runs better means too rich!this wont hurt it just makes it run cooler and cost you money in fuel and spark plugs and a loss of performance.

adam bike doctor, January 2010