I'm sorry, Matty, but since I have no experience with installing only part of a high performance kit on a 300, I don't know the value of the needle in the jet kit.

However (but this may be comparing apples to oranges), I made significant reductions in the restrictions in the intake and exhaust tracts on my new XR400R, which required a larger main jet and a larger pilot jet, but required no change to the needle or circlip position at all. In your shoes, I'd remove the backfire screen from the air filter, install the IDS pipe, and buy 4 larger size main jets and pilot jets (from 3 sizes richer to 6 sizes richer), installing the largest of each for the initial tests, and then reducing the jet sizes as needed by fine tuning testing. Re-jetting a carb is often a frustrating and time consuming process, but it sure is worth it when you get it just right!

Gordon Banks
Huntsville, AL
2000 Honda XR400R
1999 Honda 450ES 4x4
1997 Honda 300 4x4
1947 Body

 

Without the needle the Dyno jet kit is useless. You need to have it.

Jolly