Jetting help

[zrpilot]

Originally posted by BEAVER.989
There is some great information here. I do have a question, though. Why is it that the needle is considered the most important part of the equation, yet it gets paid so little attention?

I see a lot of jetting recommendations involving a new main and piolot, but stock needle position. These recommendations come from both forum members and pipe manufacturers(Curtis Sparks, for example)...

Is it because of the fact that when you adjust both the main and pilot that it usually has a big enough effect on the needle? Or is it just that most people don't understand enough about the needle to mess with it?

The needle is probably the most complicated and difficult jetting variable to deal because it is made up of three things, diameter, taper, and clip position. IMO, the only way to effectively fine tune a needle is on a dyno with a wide band O2 sensor.

DIAMETER: The needle diameter controls the jetting just above the pilot jet, right as the engine begins to pull. The needle diameter is felt in the ¼ throttle range. A bigger diameter needle makes this range leaner, whereby a smaller diameter needle makes this range richer.

TAPER: The needle taper is the angle of the needle at its lower half. The taper works the transition between the mid-range and full throttle/main jet (¾ throttle position). The taper is the least sensitive function of the needle. Changes in the taper have very mild subtle changes in the jetting. The taper also affects the main jet size your carburetor requires.

(CLIP POSITION) LENGTH: The needle length is determined by the clip position (grooves at top of needle) setting on the upper portion of the needle. On most needles there are 5 clip positions. The top clip position is referred to as #1 and is the Leanest setting. The clips are referred to in numerical order with the bottom position being #5, the Richest. The clip/length setting covers the largest percentage of jetting in your carburetor. With an emphasis at ½ throttle, the clip setting will bleed both up and down to some degree to cover a wide portion of the midrange jetting.

Ideally you like to run the needle setting in either the 3rd or 4th clip position, if possible. The needle clip jetting is especially critical to your machines reliability because on average more time is spent in the mid-range than any other part of the throttle.




Whew!

[BikeSwimLaugh]

And all this is adjusted in the transmission, right?

Actually, that all makes perfect sense. It's all about regulating the fuel in proper proportion and in accordance with the engines needs to optimal performance and a consistent air/fuel mixture across the rpm band.

Okay, so how do we take into account the bi-polar matrix alignment of the dilithium crystals when the cross-grid field array is misaligned with the subdivision generator exponantor?? The sub-space field accelator would clearly have to be aligned with the grid to radiate a cohesive bond with the anti-matter flux capacitor. Ahhhh....I get it now!

[BEAVER.989]

So ZR, when an exhaust manufacturer recommends a larger pilot and main, but stock needle in the stock position, do you believe this is a bad recommendation?

Do they do this simply because they don't have enough confidence in the lamen to handle the task, or could it be as I mentioned(and read somewhere), that the adjustments to the pilot and main effect the needle, as well?

[Pabst_Powered]

i think my quad needs this done so im really looking in to it, i have a t-4 slip- on and a k&n, pro circuit calls for a 158 main and 58 pilot for this pipe on a ex, i pulled the main out and its still the stock 148(pipe and filter were on when i bought it), my plug reads good but i do have a very slight backfire at high rpm's when i let off the thottle...any suggestions, thanx

[zrpilot]

Originally posted by BEAVER.989
So ZR, when an exhaust manufacturer recommends a larger pilot and main, but stock needle in the stock position, do you believe this is a bad recommendation?

Do they do this simply because they don't have enough confidence in the lamen to handle the task, or could it be as I mentioned(and read somewhere), that the adjustments to the pilot and main effect the needle, as well?

I don't know why they do that... I suppose it might be as you say, in that the average rider can't or won't adjust the needle.

The pilot and the main jet do affect the needle circuit, but only to a VERY small degree.

[BikeSwimLaugh]

Originally posted by Pabst_Powered
i think my quad needs this done so im really looking in to it, i have a t-4 slip- on and a k&n, pro circuit calls for a 158 main and 58 pilot for this pipe on a ex, i pulled the main out and its still the stock 148(pipe and filter were on when i bought it), my plug reads good but i do have a very slight backfire at high rpm's when i let off the thottle...any suggestions, thanx

Hmmm....I'm running an HMF slip-on and K&N as well, they called for a 152 and once the lid on the air-box is removed it seems to run just fine with no back-firing (as you made mention of).

LOL...I had previously thought I was stumbling at the top-end, but turns-out I'm just bouncing off the rev-limiter and have been used to high-revving 2-strokes. These engines do their thing at low/mid range anyways.

I'd try going down to a 154, 158 seems a bit steep...perhaps that's the issue. Please let us know what finally works the best: the slip-in exhaust and air-filter are seemingly the most classic mod's done, so a nice combination of jetting alteration would be much appreciated by all.

[Pabst_Powered]

Originally posted by BikeSwimLaugh
Hmmm....I'm running an HMF slip-on and K&N as well, they called for a 152 and once the lid on the air-box is removed it seems to run just fine with no back-firing (as you made mention of).

LOL...I had previously thought I was stumbling at the top-end, but turns-out I'm just bouncing off the rev-limiter and have been used to high-revving 2-strokes. These engines do their thing at low/mid range anyways.

I'd try going down to a 154, 158 seems a bit steep...perhaps that's the issue. Please let us know what finally works the best: the slip-in exhaust and air-filter are seemingly the most classic mod's done, so a nice combination of jetting alteration would be much appreciated by all.

main jet is still the stock 148, didnt put the 158 in yet, i ordered a kit from jets r us and have to see how i do

[bullett]

I only have a slip on exhaust. I've read these quads come a little lean from the dealer and I figured I better jet my quad. I put in a 42 Pilot and a 150 Main jet. Does this sound about right to you guys?

[riderssb250x]

alright guys i have a 450r carb and need help
my mods are

440 kit
hot cam stage 2
no iar box
k&n filter
Lrd pro4 full exhaust
ported and polished head


whats probably a good main pilot and needle clip position

[zrpilot]

Originally posted by riderssb250x
alright guys i have a 450r carb and need help
my mods are

440 kit
hot cam stage 2
no iar box
k&n filter
Lrd pro4 full exhaust
ported and polished head


whats probably a good main pilot and needle clip position

First fix your hot start issue.