Jet needle position?

What does raising the jet needle position do?I did this at the recomendation of some members of this site but I never bothered to find out why.Bike runs fine but Im just wondering what that effects.
Tony

Raising the jet needle on any carb will create a richer fuel mixture 'earlier' as such - I'm new to kz's ( but not to bikes)n so I'm not sure if there is an inherant problem with the mixture/circuit crossovers in 650 carbs - I'm sure someone else will chip in on this.
Generally raising the needle will advance the time of changeover between mixture circuits - from pilot to the main circuits.
If 650s are known for getting bogged down ? this may be a an attempt to sort this out.
Cheers
Ben

BoZ650 wrote:

What does raising the jet needle position do?I did this at the recomendation of some members of this site but I never bothered to find out why.Bike runs fine but Im just wondering what that effects.
Tony

Just did this on my 750 twin after I installed MAC 2-1 pipes, and here is what mine did:

The pilot jet determines performance at idle and VERY LIGHT THROTTLE opening up to about 2k RPM.

Between 2k and 3k, I had a weak throttle response and lack of power. On a 750 twin, that is the most used operating range so it really sucked. raising the needle (lower the clip) to get richer mix fixed it. The needle position has most effect at this "off idle" throttle response from about 0 - 1/4 throttle opening in the 2K to 3k range.

YMMV

BoZ650 wrote:

What does raising the jet needle position do?I did this at the recomendation of some members of this site but I never bothered to find out why.Bike runs fine but Im just wondering what that effects.
Tony

If it runs fine, I am wondering why you would want to change the needles?

I just want to know the physics behind it,I kind of just did it without knowing why!Just Curious!

BoZ650 wrote:

I just want to know the physics behind it,I kind of just did it without knowing why!Just Curious!

The piston rising raises the needle out of the needle jet which is fed by the main jet, so as the needle raises (and the diameter of the portion of the needle inside the jet decreases)more fuel is allowed to flow by the needle and into the air stream to run the engine. Basically, raising the needle position in the piston "forward biases" everything so that a given richness occurs at a lower piston position which is a more closed throttle opening. Overall, you get a richer feed at a lesser throttle opening. If you have throttle hesitation from closed position coming open, this can cure it.

Thanks Bountyhunter that is exactly what I wanted to know.I hate to just make a adjustment and then not know why.Im trying to really learn what I am doing!
Thanks again.
Tony