OK I finally got my 250 running great so I decided to add a K&N filter and the problems started all over again, BUT before I get started I was looking for advice on which way I should go. I had originally adjusted the float level, changed the carb jets and adjusted the needle height. Now when I throttle slowly it works fine but when I go to give it a lot of throttle from the start it stalls and if you go to give it throttle while moving there is no speed. Should I change jets??? and if so what size would be recommended.

Thanks in advance

 

with only a k&n airfoliter changed, you'd still need to rejet, stock jetting for your cn250 is 38 pilot and 112 main, i found that 45 pilot and a 128 main worked the best for me. depending on you altitude where you live dictates what size you're need, so use my sizes only as a referance

 

I have rejetted to 45 and 130 previously and had it running good with the stock air box I just don't know if adjusting the needle is the way to go

 

The 'main jet' size is the 'major' adjustment factor for 30% to 100% throttle fuel / air mixture ratio.

The 'slide needle valve' adjustment is for 'fine tuning' the fuel / air mixture within the 'base range' established by the jet size.

The 'slide needle' is a fairly sophisticated way of adjusting the mixture ratio, depending upon the 'position' of the throttle.

The needle is 'thicker' when it hangs further down into the jet opening (low throttle) which 'blocks' more area of the jet hole - which makes a 'smaller net open area' of the jet at low throttle (leaner).

At higher throttle levels, the needle is drawn out of the jet, and because the needle is tapered - it blocks 'less' of the jet opening which results in a 'larger net open area' of the jet , which results in a richer fuel / air mixture at higher throttle.

If you move the needle down further 'into' the jet (via the 5 groves and e-clip) you 'lean out' the overall mixture because the needle is thicker. Conversely if you 'raise it' you richen up the mixture a bit.

The 'ramp' or 'slope' of the needle change (from skinny to fat) determines how fast the enrichment adjustment changes with each setting on the 5 groves.

On automobile carbs (Rochester Quadrajet) there were literally dozens of 'needles' available - each with is own 2 letter code - to fine tune the carb, depending upon vehicle weight, altitude, grade of fuel used, etc, etc. Unfortuneitly, on ATV carbs, I have not seen any specially tapered needles available for 'fine tuning'.

 

i would go bigger on the pilot jet, i'd try a 48 or maybe even a 50, if you're using a 130 main then i'd try a 140 and see how it runs, when you do get it to idle and accelerate correctly then you'd need to do a plug check just to make sure you're not overly rich or running lean.