what's this???

[krt400ex]

hey, all u carb guys, what is the needle clip. if u have pics that would be great. what is it's function, and what does moving it up or down do? thanks for ur help

[redexrider]

I do not have a picture, but the needle clip is a clip that goes at the top of the needle and holds it in place (keeps it from falling through and allows it to move up and down.) Pulling the needle further up and placing the clip further down on the notches will allow more fuel to flow through because less needle is there to block it. And obviously putting it more towards the top of the needle would allow less fuel. If you remove your top plate on your carb, you will see the slide. The two screws on the bottom hold the plate that holds the needle down. if you remove them (2 screws, and be carefull they are soft metal) you will expose the top of the needle. at this point you can pull the needle out. I am not positive that your stock carb has an adjustable needle, but if it does you will see the grooves at the top of the needle and the clip will be attached to one. This is where your adjusting will take place. The notches are numbered from top to bottom. Further down more fuel, further up less fuel.

[GPracer2500]

Here's what the clip itself looks like:

http://suzuki-gt.co.uk/shop/images/13394-10010.jpg

Here's an adjustable jet needle (on the left) with the clip in place. Notice the slots on the top of the needle. Each slot is a possible clip position. The jet needle on the right is not adjustable using the "clip-and-slot" system.

http://www.cmgonline.com/racing/articles/04_ZX7Project/BigP/carb_needles_bg.jpg

In order to adjust a "non-adjustable" jet needle you must use shims. And you can only adjust it richer (not leaner) using this method. Here's a non-adjustable jet needle with a couple of shims slidding on:

http://www.dm.net/~bahwolf/bb2004/shims.jpg

The purpose behind using clips or shims is to raise (or lower) the jet needle in the slide. Raising the jet needle positions it so that it's on a thinner part of it's taper when it passes through the needle jet.

Note: the "needle" is technically called a jet needle. The needle jet is a different piece. The needle jet is the collar that sizes the opening in the venturi that leads down to where the main jet is located.

If the jet needle is on a thinner point in it's taper for any given throttle postion than that leaves more space for fuel to get through--i.e. richer jetting.

The jet needle's clip postion affects fueling from 1/8 to 3/4 throttle. Other (fixed) characteristics of the jet needle overlap and go beyond that range of throttle positions. Since the clip position is the only thing that's adjustable (barring actually changing the needle) we usually just think of the jet needle as having an affect on the jetting from ~1/8 to 3/4 throttle.

[GPracer2500]

Here's another pic of an adjustable jet needle. This one has a needle jet next to it. (I know, I know--jet needle, needle jet--it's a little confusing) Needle jets and jet needles usually come as a set. The needle jet is not something you change to adjust the carb's tuning.

http://img53.imageshack.us/img53/1849/p8150037vz0.jpg

[krt400ex]

thanks for the pics gpracer, and for the help everyone. i got another ques. though

why would u richen or lean out the jet needle?? why not just change main jets??

[GPracer2500]

When you're at--let's say--half throttle, the needle is blocking the space that flows fuel from the main jet. If your fueling is too rich or too lean at 1/2 throttle then changing your main will do next to nothing to help that. The needle is what is restricting the flow of fuel at that throttle position--not the main jet. It's only when the needle gets pulled way up out of it's hole (when you're at 3/4 throttle or more) that the main jet is flowing its load of fuel unrestricted. That's when main jet changes are appropriate--3/4 to WOT.


There's some overlap between circuits, but certain circuits dominated the fueling at certain throttle positions.

[krt400ex]

Originally posted by GPracer2500
When you're at--let's say--half throttle, the needle is blocking the space that flows fuel from the main jet. If your fueling is too rich or too lean at 1/2 throttle then changing your main will do next to nothing to help that. The needle is what is restricting the flow of fuel at that throttle position--not the main jet. It's only when the needle gets pulled way up out of it's hole (when you're at 3/4 throttle or more) that the main jet is flowing its load of fuel unrestricted. That's when main jet changes are appropriate--3/4 to WOT.


There's some overlap between circuits, but certain circuits dominated the fueling at certain throttle positions.

i see, thanks