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Hi guys and gals

I know this has been asked and answere before but i want to tailor this to my problem and would appreciate any help. I have just bought my bike and everything exceeds expectations (first zxr400 !) but the bike had a splutter when gently rolling the throttle on and was advised to try a new set of carbs.......so me being me i got a set off fleabay and a nice k&n filter to go with it. Just had my brother round and fitted my new carbs and filter but he had to leave the top plastic plate and snorkel out of the airbox so currently wide open at top. The bike fired straight up but when took for a test drive works fine up until about 7-8k revs then just stopps revving and sounds restricted, no problems with spluttering when gently rolling throttle on now tho.

Simple questions now

Should i need to dynojet my carbs now ? with airfilter and scorpion race can and should this solve my problem

Can i fit a jet kit myself and roughly guess jet size until i get it rolling roaded ? if so what size jet will go with k&n and race can ?

Should my airbox be open at top now ?

any help would be greatly greatly appreciated

Because every bike is individual there is no definitive answer, however Dynojet make a kit that is a good base line acroos them all - they have done all the dyno time developing the kit but your not sure what pipe they are using but certainly will be free flowing ( Seeing as they are in the US I guess a D&D ).

Never seen the K&N filter your on about but as a replacement for the standard filter it should not require rejetting , however you are running with the lid off your airbox That is leaning it right out hence its falling on its butt at 7Kish - you need to up the mains , what by ???? But jump at least 5 at a time till it revs clean.

Your going to want a nice sooty deposit at the end of your can , check plugs too for colour - best done as a "plug chop" which involves hopunding it along , pulling clutch in and cutting engine too. Coast in and remove plugs too see what colour they are - mind and take tools with you !

TRY , going back to normal airfilter with the airbox sealed up and see how it runs then get involved fetling it for your K&N filter, but pray tell why doesn't the lid of airbox fit and indeed the other parts you removed ? sounds like its a wrong filter