Honda Spree and Elite 50 Forums

I copied this to a word doc, and now can't find the original poster, please let me know so i can give you credit.

If your bike's motor is not mechanically sound, then all the jetting in the world will not help. With all of the above conditions met, you should be able to jet your carburetor following these steps:

Step 1: DETERMINE THE CORRECT NEEDLE AND OR NEEDLE JET.

Whether or not your carburetor is a MIKUNI or a KEIHIN, it does not matter. This is the most important step in jetting your carburetor--period!

1. Remove the main jet.
2. Place needle clip in mid-position.
3. Start motor and run it on the stand.

Condition: Motor running and main jet out. Needle or needle jet is correct: Carburetor should run clean to approximately 3/4 throttle. From 3/4 throttle to full throttle, the motor should start to break up as a result of too rich condition.
Correction: None needed.

Condition: Needle or needle jet is too rich. Carburetor runs clean to approximately 1/2 throttle but breaks up before 3/4 throttle as a result of too rich condition.
Correction: Mikuni replace needle jet with next leaner and test again. Keihin replace needle with next leaner diameter and test again.

Condition: Needle or needle jet is too lean: Carburetor runs clean beyond 3/4 throttle and has an erratic throttle response.
Correction: Mikuni replace needle jet with next richer and test again.
Keihin replace needle with next richer diameter and test again.

The emphasis here is to find the correct needle or needle jet diameter, which will allow more fuel to pass than is needed but not so much that the needle itself has no control below 3/4 throttle.

Step 2: DETERMINE THE CORRECT PILOT JET.

1. Make sure the bike is warmed up if at all possible.
2. Main jet out.
3. Needle clip in mid position.
4. Turn air screw all the way in then 1/4 turn out.
5. Start motor and run it on the stand.
6. Adjust idle so the bike will just barely idle.

Condition: Motor running and main jet out.

PILOT JET CORRECT: With one hand on the throttle maintaining RPM at approximately 1/8 throttle, turn air screw 1/4 turn at a time clock wise until you bottom it out. Motor should become slightly erratic and you should have to play with throttle to maintain RPM. Start turning air screw counter clock wise, 1/4 turn at a time until you have reached 2 3/4 turns out. Between 1 1/4 and 2 1/4 turns, your motor should have reached its highest RPM maintaining a steady throttle. Adjust air screw again between 1 1/4 and 2 1/4 until you have determined highest RPM. Quick throttle response should be clean without bog.

PILOT JET TO RICH:
RPM does not reach a peak between 1 1/4 and 2 1/4 turns, stays the same or keeps rising out to 2 3/4 turns.
Correction: Mikuni replace pilot jet with next leaner and test again. Keihin replace pilot jet with next leaner and test again.

PILOT JET TO LEAN:
RPM does not become erratic and motor maintains throttle when air screw is turned all the way clockwise.
Correction: Mikuni replace pilot jet with next richer and test again. Keihin replace pilot jet with next richer and test again. Remember, with a steady throttle approximately 1/8, there should be a distinct difference in RPM from 1 1/4 turns to 2 1/4 turns if the pilot jet is correct. The emphasis here is to find a pilot jet that will run crisp without bog and without the main jet.

Step 3: DETERMINE THE CORRECT MAIN JET.

The main jet selection process is easy once you have the correct needle diameter or needle jet. You now only have to correct a rich condition from 3/4 throttle on up and you know what a rich condition sounds like. Your pilot circuit is correct and without bog.

1. Replace main jet with one that is at least two sizes smaller.
2. Needle clip in mid position.
3. Start motor and run it on the stand.

By replacing the main jet with one that is too small, you are looking for a condition that is too lean. You adjust your main jet from a too small to lean condition.

Condition: Motor running and main jet in.

MAIN JET CORRECT:
Carburetor should run clean and crisp to full throttle.
Correction: None needed.

MAIN JET TOO RICH:
RPM reaches a peak slowly with a deep sound. Excess fuel and oil mixture at end of silencer. Spark plug fowls easily and is dark in color.
Correction: Mikuni replace main jet with next leaner and test again. Keihin replace main jet with next leaner and test again.

MAIN JET TOO LEAN:
RPM reaches a peak quickly but erratic. A quick full snap open of throttle causes the motor to hesitate BEWAH sound or a complete bog. Motor sounds like it has a ring to it. End of silencer white. Spark plug is white in color.
Correction: Mikuni replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. Keihin replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. The emphasis here is find a main jet that is just rich enough to allow you snap the throttle wide open without the motor bogging as a result of the main being too lean. Should be a quick crisp throttle with no hesitation.

Step 4: DETERMINE THE CORRECT NEEDLE TAPER AND CUT AWAY.

This step in the jetting process can be made very simple if you remain close to stock. However, your needle taper is adjusted for 1/2 throttle to 3/4 throttle. Start off with a rich taper (shallow taper angle) and keep going leaner (steeper taper angle) until it will not maintain constant RPM at 1/2 throttle (runs erratic). Go back to the leanest taper angle that ran the smoothest at 1/2 to 3/4 throttle and that should be the correct taper.

The needle taper final test should be under track conditions with the greatest effect entering and exiting corners. Do not change the needle diameter or needle jet size during this process because that has already been determined. Adjust taper and throttle cut away only.

Throttle cut away effects from idle to 1/4 throttle. The correct cut away will maintain steady 1/8 throttle with quick throttle response. Generally the stock cut away is very close. Experiment with different cut away until it maintains the best response to 1/4 throttle.

That's it, if you spend the time jetting correctly, the benefits you will gain definitely out-weigh way the time spent. Take the guesswork out jetting by following a procedure that has been given or one you have laid out yourself. Keep the black magic process out of your tuning tricks and you will be better off for it.

From an article by Don K. Courtney. Link is dead now.
Jetting Tip: pilot jet and air screw

To check to see if your pilot jet and air screw are adjusted right, warm up the motor and let it idle as low as possible while still running smooth. From idle, whack the throttle wide open then let it close completely. Listen to the motor. If it bogs right when you whack the throttle open, then revs up, turn the air screw in 1/2 turn then try again. Do this until it revs up crisply. After the motor revs up, listen to it revving back down. If the revs drop quickly, and the motor starts to bog, and/or die, then you're too rich on the air screw, back it out 1/4 turn at a time. If after you let the throttle off the motor tends to run on and on while revving down very slowly, you're too lean and need to turn the air screw in 1/4 turn at a time. You want the revs to come up from idle quickly and smoothly, then drop back down to idle the same way. If you turn the air screw all the way in and it still needs to go further, then you will need a larger pilot jet. The opposite is also true: if you are backing the screw out so far that it darn near falls out, you will need a smaller pilot jet.

From http://domlnator.tripod.com/id8.html
Needles

The three letters refer to different aspects of the needle. In turn you have:

1. Taper: most effective at ›- throttle.
2. Length/clip position: most effective at ¼-› throttle.
3. Diameter: most effective towards ┬╝ throttle.

Higher taper letters are richer; for diameter and length, higher letters are leaner.

For example, going off a standard JJH needle (our old N80F needle was close), and comparing with our other needles:

* GJH: leaner taper, so leaner at ›- throttle.
* LJH: richer taper, so richer at ›- throttle.
* JJK: leaner diameter, so leaner towards ┬╝ throttle.
* JJF: richer diameter, so richer towards ┬╝ throttle.

for anybody interested i found 2 cool websites about these needles,
http://keihincarbs.com/images/spilli-PEPWK2628.jpg
http://www.scribd.com/doc/78484988/K-U-Needle-Charts

It looks like the k44, k46, k50 came from one manufacturer and the jjh, jjk, jjf came from another. Now I gotta find the other 4 needles that came from treatland, and also disect the charts to show a good comparison for them.

edit: also found this one, http://scootrs.com/tech.cfm?tip=tunecarb#e

The part where you take the main jet out to see if the needle is correct is wrong. There is always a overlap some where and the main jet starts just about 1/2 if not just a tad sooner. The pilot jet over laps into the main just past 1/2 so you will get a false read on the jetting for sure if you follow those steps.

i had some news but still is running crappy. going to try smaller pilot jet.

And i think maybe the plug is fouled, so i'm going to go buy some more.

What does it mean if it can't accelerate from 1/2 to 3/4 throttle, but if you whack it open from 0-3/4 it'll accelerate just fine?

i swear i've tried smaller pilot jet, bigger pilot jet, new spark plug, different clip on needle. Can't seem to get it to run right.

steffen707 wrote:What does it mean if it can't accelerate from 1/2 to 3/4 throttle, but if you whack it open from 0-3/4 it'll accelerate just fine?

i swear i've tried smaller pilot jet, bigger pilot jet, new spark plug, different clip on needle. Can't seem to get it to run right.

With the throttle at WOT, only the main jet is controlling fuel, regardless of engine RPM.

well at least it will idle and run at WOT, everything in between needs work.

Okay, I decided to go back to the needle that came with the 24mm oko carb, it was the 6kb, with the 50pilot and needle on center clip it was gutless from 1/2-3/4. I put the clip up one, which would be leaner, and was surprised that now it transitions from 1/2 to 3/4 and even a brief WOT pretty well. I didn't think the needle clip would effect the 1/2-full that much, but it did.

I noticed that when i was at 30mph and close the throttle, the temps would rise a bit. From about 280-290, if I give a bit of throttle back then it will drop back. My CHT isn't instant, it takes a moment or so to show the changes. I'm assuming this is a lean condition from the pilot jet? So I went from 50-52 on the pilot. It still seems to rise when the throttle snaps shut. Should I go bigger yet on the pilot?

It was also doing this..........When you would accelerate from a stop it would accelerate decently at 1/2 throttle, but then if you crack it open for a second then back it off to 1/2 throttle it would make way more power and accelerate much faster.

I really wish my wideband o2 sensor on my drag car was on my scooter right now, that or a bit of experience in carb tuning.

steffen707 wrote:It was also doing this..........When you would accelerate from a stop it would accelerate decently at 1/2 throttle, but then if you crack it open for a second then back it off to 1/2 throttle it would make way more power and accelerate much faster.

I really wish my wideband o2 sensor on my drag car was on my scooter right now, that or a bit of experience in carb tuning.

That bit of info tells me you are too lean in the midrange (1/2 to 3/4 throttle).

Thanks bear. From the picture you showed earlier, 1/2-3/4 is mostly the needle taper right? Would increasing the pilot jet help this at all? I was thinking I might have to increase it to deminish that closed throttle deceleration temp spike.

Some but above 1/2 throttle the pilot is adding very little fuel compared to the main jet circuit.

If your only getting a 10deg heat spike I wouldn't worry to much. If its more like 30+ then worry. A anything bigger than a 50 pilot is to much. Where do you have the air fuel screw? That will play a roll to as that effects the 0-little past 1/4 throttle

Thanks for all the help guys, I really do appreciate it.

I currently have the screw 1.5 turns out. I was thinking about richening that up a little and then see if the heat spike goes down. From the few times I was watching its at most 10deg, probably more like 5. Its not an instant update with the trailtech vapor, so I can't tell exactly.

Baka, do you suggest going larger on the main jet or should I try to find a needle with same length, same diameter, but different taper, to cure my "It was also doing this..........When you would accelerate from a stop it would accelerate decently at 1/2 throttle, but then if you crack it open for a second then back it off to 1/2 throttle it would make way more power and accelerate much faster." problem?

You will also need to play with the trans too. They both work together. The more power your motor makes or loses power will effect how the trans will work. The cvt transistions the belt with not only rpm but with torque too. So playing with different combo of trans parts is needed to satisfy your feel of how the bike rides. So adjusting one section will effect another section. Its a back and forth thing till you get every section close.