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Author Topic: Jetting data base  (Read 10950 times)

Offline rsss396

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Jetting data base
« Reply #15 on: July 15, 2013, 11:55:44 AM »
[h=3]JETTING: Getting the most out of your bike[/h]I have had a lot of questions in reference to my article on carburetor jetting, so I have simplified the procedures to elevate as many questions as possible.
For whatever reason it becomes necessary to re-jet a carburetor, it is without a doubt a nightmare if you do not have a procedure to follow. The following is nothing more than a technique, procedure, steps or whatever you want to call it to help identify and isolate the carburetor circuit involved.
You can only begin re-jetting your carburetor if the following conditions are met:

  • Top end is in good condition.
  • Bottom end is in good condition. Crank seals.
  • Spark plugs, air filters, reeds and so on.
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:
[h=3]Step 1: DETERMINE THE CORRECT NEEDLE AND OR NEEDLE JET.[/h]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!

  • Remove the main jet.
  • Place needle clip in mid-position.
  • 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.
[h=3]Step 2: DETERMINE THE CORRECT PILOT JET.[/h]
  • Make sure the bike is warmed up if at all possible.
  • Main jet out.
  • Needle clip in mid position.
  • Turn air screw all the way in then 1/4 turn out.
  • Start motor and run it on the stand.
  • 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.
Anyone looking for a great builder I highly recommend the following.
For CP products dealers I would recommend:
Arlan at LED(site sponsor), Pete Schemberger at Hybrid Engineering, Mat Shearer at Shearer Custom Pipes, Dennis Packard at Packard Racing, and Nate McCoy of McCoys Peformance.

Other great builders I also would recommend: Neil Prichard, Jerry Hall, Bubba Ramsey and James Dodge.

Offline rsss396

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Jetting data base
« Reply #16 on: July 15, 2013, 11:56:56 AM »
[h=3]Step 3: DETERMINE THE CORRECT MAIN JET.[/h]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.

  • Replace main jet with one that is at least two sizes smaller.
  • Needle clip in mid position.
  • 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.
[h=3]Step 4: DETERMINE THE CORRECT NEEDLE TAPER AND CUT AWAY.[/h]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.
Anyone looking for a great builder I highly recommend the following.
For CP products dealers I would recommend:
Arlan at LED(site sponsor), Pete Schemberger at Hybrid Engineering, Mat Shearer at Shearer Custom Pipes, Dennis Packard at Packard Racing, and Nate McCoy of McCoys Peformance.

Other great builders I also would recommend: Neil Prichard, Jerry Hall, Bubba Ramsey and James Dodge.

Offline rsss396

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Jetting data base
« Reply #17 on: July 15, 2013, 11:57:42 AM »
[h=3]Jetting Tip: pilot jet and air screw[/h]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.

[/HR][h=3]Needles[/h]The three letters refer to different aspects of the needle. In turn you have:

  • Taper: most effective at - throttle.
  • Length/clip position: most effective at - throttle.
  • 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.
[TABLE=class: t-sm]
[TR]
[TH=colspan: 3][/TH]
[TH=colspan: 13]Diameter              [/TH]
[/TR]
[TR=bgcolor: #d7d7d7]
[TH]Taper (A)
in degrees[/TH]
[TH](L1) Length
in mm[/TH]
[TH][/TH]
[TH]D=
2.405[/TH]
[TH]E=
2.405[/TH]
[TH]F=
2.415[/TH]
[TH]G=
2.425[/TH]
[TH]H=
2.435[/TH]
[TH]J=
2.445[/TH]
[TH]K=
2.455[/TH]
[TH]L=
2.465[/TH]
[TH]M=
2.475[/TH]
[TH]N=
2.485[/TH]
[TH]P=
2.495[/TH]
[TH]Q=
2.505[/TH]
[TH]S=
2.525[/TH]
[/TR]
[TR]
[TH]G
2 26'[/TH]
[TH]F=22.25[/TH]
[TH]Rich[/TH]
[TH=colspan: 4][/TH]
[TH]GFH[/TH]
[TH][/TH]
[TH]GFK[/TH]
[TH=colspan: 6][/TH]
[/TR]
[TR]
[TH]J=25.40[/TH]
[TH]Lean[/TH]
[TH]GJH[/TH]
[TH]GJK[/TH]
[/TR]
[TR]
[TH=colspan: 16]
[/HR][/TH]
[/TR]
[TR]
[TH]H
2 45'[/TH]
[TH]F=22.25[/TH]
[TH]Rich[/TH]
[TH=colspan: 2][/TH]
[TH]HFF[/TH]
[TH]HFG[/TH]
[TH]HFH[/TH]
[TH][/TH]
[TH]HFK[/TH]
[TH][/TH]
[TH=colspan: 5][/TH]
[/TR]
[TR]
[TH]K=25.85[/TH]
[TH][/TH]
[TH]HKF[/TH]
[TH]HKG[/TH]
[TH]HKH[/TH]
[TH]HKJ[/TH]
[TH]HKK[/TH]
[TH]HKL[/TH]
[/TR]
[TR]
[TH]L=27.20[/TH]
[TH]Lean[/TH]
[TH][/TH]
[TH]HLG[/TH]
[TH]HLH[/TH]
[TH]HLJ[/TH]
[TH=colspan: 2][/TH]
[/TR]
[TR]
[TH=colspan: 16]
[/HR][/TH]
[/TR]
[TR]
[TH]J
3 00'[/TH]
[TH]F=22.25[/TH]
[TH]Rich[/TH]
[TH=colspan: 3][/TH]
[TH]JFG[/TH]
[TH][/TH]
[TH]JFJ[/TH]
[TH][/TH]
[TH]JFL[/TH]
[TH][/TH]
[TH]JFN[/TH]
[TH]JFP[/TH]
[TH]JFQ[/TH]
[TH]JFS[/TH]
[/TR]
[TR]
[TH]G=23.60[/TH]
[TH=colspan: 10][/TH]
[TH]JGN[/TH]
[TH][/TH]
[TH]JGQ[/TH]
[TH]JGS[/TH]
[/TR]
[TR]
[TH]J=25.40[/TH]
[TH][/TH]
[TH]JJD[/TH]
[TH]JJE[/TH]
[TH]JJF[/TH]
[TH]JJG[/TH]
[TH]JJH[/TH]
[TH]JJJ[/TH]
[TH]JJK[/TH]
[TH]JJL[/TH]
[TH]JJM[/TH]
[TH]JJN[/TH]
[TH]JJQ[/TH]
[TH]JJS[/TH]
[/TR]
[TR]
[TH]L=27.20[/TH]
[TH]Lean[/TH]
[TH=colspan: 2][/TH]
[TH]JLF[/TH]
[TH]JLG[/TH]
[TH]JLH[/TH]
[TH]JLJ[/TH]
[TH=colspan: 6][/TH]
[/TR]
[TR]
[TH=colspan: 16]
[/HR][/TH]
[/TR]
[TR]
[TH]K
3 15'[/TH]
[TH]L=27.20[/TH]
[TH=colspan: 3][/TH]
[TH]KLF[/TH]
[TH]KLG[/TH]
[TH]KLH[/TH]
[TH]KLJ[/TH]
[TH]KLK[/TH]
[TH=colspan: 6][/TH]
[/TR]
[TR]
[TH=colspan: 16]
[/HR][/TH]
[/TR]
[TR]
[TH]L
3 33'[/TH]
[TH]G=23.60[/TH]
[TH]Rich[/TH]
[TH=colspan: 3][/TH]
[TH]LGG[/TH]
[TH]LGH[/TH]
[TH]LGJ[/TH]
[TH][/TH]
[TH]LGL[/TH]
[TH][/TH]
[TH]LGN[/TH]
[TH][/TH]
[TH]LGQ[/TH]
[TH]LGS[/TH]
[/TR]
[TR]
[TH]J=25.40[/TH]
[TH]Lean[/TH]
[TH]LJG[/TH]
[TH]LJH[/TH]
[TH]LJJ[/TH]
[TH=colspan: 6][/TH]
[/TR]
[TR]
[TH=colspan: 16]
[/HR][/TH]
[/TR]
[TR]
[TH]M
3 50'[/TH]
[TH]J=25.40[/TH]
[TH]Rich[/TH]
[TH=colspan: 9][/TH]
[TH]MJN[/TH]
[TH][/TH]
[TH]MJQ[/TH]
[TH]MJS[/TH]
[/TR]
[TR]
[TH]L=27.20[/TH]
[TH]Lean[/TH]
[TH=colspan: 7][/TH]
[TH]MLL[/TH]
[TH][/TH]
[TH]MLN[/TH]
[TH]MLQ[/TH]
[TH]MLS[/TH]
[/TR]
[/TABLE]
Anyone looking for a great builder I highly recommend the following.
For CP products dealers I would recommend:
Arlan at LED(site sponsor), Pete Schemberger at Hybrid Engineering, Mat Shearer at Shearer Custom Pipes, Dennis Packard at Packard Racing, and Nate McCoy of McCoys Peformance.

Other great builders I also would recommend: Neil Prichard, Jerry Hall, Bubba Ramsey and James Dodge.

Offline 05450r

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« Reply #18 on: August 02, 2013, 10:11:25 AM »
My old stock cyl setup


Mixture ratio and fuel: 32:1 vp c12 HP2 oil


Carb Type/size:38 pwk as


Main Jet size: 168-170


Slow (pilot) Jet size:50


AirScrew (number of turns out): 1.5


Needle (what groove is the clip in, Brand, etc): DGL


Reed brand and type: Boyesen Rad valve fiberglass reeds


Airbox/filter/eliminator: 06' 450r Venon eliminator w/ Uni filter


Pipe: Sparks MX


Engine Displacement: 265cc oem cyl


Compression ratio: 230 psi with 19cc dome


Porting type: Jerry Hall mx porting


Altitude: 600-700ft above sea level

Cr250 ignition,Br8es at .22 gap
04 450r XC
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Offline 05450r

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« Reply #19 on: August 02, 2013, 10:16:49 AM »
New setup,Baldwin ported pro-x 265pv


Mixture ratio and fuel: 32:1 vp c12 Hp2 oil


Carb Type/size: 38pwk as


Main Jet size: 182


Slow (pilot) Jet size:52


AirScrew (number of turns out):1.5


Needle (what groove is the clip in, Brand, etc): Dgl middle groove


Reed brand and type:Cr250 intake and cage,spacer,fiberglass reeds


Airbox/filter/eliminator: JL eliminator,86 boot,Uni filter


Pipe: Sparks TT,Dg silencer


Engine Displacement: 265cc


Compression ratio:240psi


Porting type: Baldwin ported Mx


Altitude: 600-700 ft above sea level

01' Cr250 ignition,br8es,.22 gap
« Last Edit: August 09, 2013, 09:42:13 AM by 05450r »
04 450r XC
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Offline 05450r

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« Reply #20 on: January 24, 2014, 12:46:50 AM »
Bump, need more people to build this up!
04 450r XC
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Offline havinnoj

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« Reply #21 on: January 24, 2014, 10:43:53 AM »
Pro-X 310 (300) Dune Port

Mixture ratio and fuel: 32:1, VP C12 or similiar, Klotz R50

Carb Type/size: Keihin 38 PWK/AS

Main Jet size: 195

Slow (pilot) Jet size: 55

Air Screw (number of turns out): 2

Idle Screw(number of turns out): 1.25

Needle (what groove is the clip in, Brand, etc): Not sure

Reed brand and type: Boyseen Rad

Airbox/filter/eliminator: Stock boot, open K&N with Outerwears

Pipe: Curtis Sparks TT

Engine Displacement: 297

Compression ratio: 235psi

Porting type: Dune port from Dave Moore Racing

Altitude: Sea Level

Offline rablack21

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« Reply #22 on: January 24, 2014, 10:52:29 AM »
ESR 310PV with TRX 9 Port

    Mixture ratio and fuel: 50:1, Benton Oil 110 race fuel, Amsoil Dominator

    Carb Type/size: Keihin 38 PWK/AS

    Main Jet size: 172-175

    Slow (pilot) Jet size: 50

    Air Screw (number of turns out): 2

    Idle Screw(number of turns out): 1.5

    Needle (what groove is the clip in, Brand, etc): DGH 3rd clip

    Reed brand and type: Delta Force 3

    Airbox/filter/eliminator: Stock box, with airbox outerwear in place of lid, UNI filter

    Pipe: Curtis Sparks MX

    Engine Displacement: 293cc? stock bore

    Compression ratio: 205psi

    Porting type: ESR TRX 9

    Altitude:  675 feet above sea level

    Ignition: CR250 ignition w/ B8es

Offline mwiley

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« Reply #23 on: March 19, 2014, 11:36:53 AM »
Mix= 32:1 amsoil/112 Dragon

Carb= 38mm Air stryker

Pipe= LRD Adjustable with FMF quiet core silencer

Air box= Unifilter with slots milled in airbox lid

Reeds= Boyseen Rad valve

Bore= 67.25/255cc

UCCR= 14.85/1

Compression= 230psi

Porting= Sometype (not sure what rpm range)

Altitude= 850ft

Main jet= 178

Slow jet= 50

Air screw= 2 turns out

Needle= CEJ with clip in 3rd position

Temp= 65 degrees

Spark plug= BR8ES gapped at .022