the needles sit inside the main jet and gradually come out as the throttle is turned till at full throttle the needle is more or less out of the jet allowing it to be fully uncovered. So they are interactive, or in other words one's size affects the other. It's a balancing act. say your bike is just right with 125 mains and Thruxton needles. If you then went to TBS needles which aren't as rich, the mains would need to get larger and richer to keep the balance. When at full throttle even tho the mains are said to be on thier own, the needles are still adding some influence and visa versa. So if you increase your mains, the hole is bigger and therefore the needles would let more mixture thru so you'd have a richer midrange w/o even having changed the needle length or taper. This is why you're supposed to get the mains right before trying different needles/shims. Hope that was clear...the best i can describe it at the moment.On 2006-11-16 13:10, kcnlisa wrote:
Can anyone give me a logical reason why it calls for smaller jets when you plug TBS needles into the jetting calculator?