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Motorcycle Repair/Dynojet stage 1,4 with Kerker exhaust on YX600


Hello William

Yx600 Radian 1986, with dynojet stage 1,3 and Kerker exhaust, and aftermarket pods.

I previously had Dynojet 128, main jets at 3rd ring, and was getting lean symptoms:

1. needed full choke to start
2. As bike heated up had to reduce airflow/idle to correct for idling at 2500-3500 on deceleration.
3. Bike was popping/backfiring flames at end of exhaust.
4. tried tape on pods, did not help.


Have moved dynojet needles to grove #4.


1. do not need choke (75 degres F)
2. No popping back firing
3. Bike idles at 1500 from cold to hot
4. Still have tape on pods.
5. set air/fuel mixture down to 3 turns.

Q1: Wondering if stage 1,3 recommendation for the bike should not be qualified with a possible 1,4 recommendation if running lean

Q2: are the DJ128 main jets the best bet or should i consider 124, or higher than 128.
The bike has smooth acceleration, previously surged at 3000 when main jets kicked in.

Thanks for your Help in advance


First Off. backfiring and flames is a Valve or Timing Issue.
Popping is a sign of a Lean Fule to Air ratio.
I would keep the #128 Main jets and Lower the E-Clip on the jet Needles to raise
the jet Needle a bit to give a richer fuel to Air ratio when throttle is applied.
There is a Tool that Helps with this Fuel to Air Ratio.
Gunson Colortune Tool..
You can leave the Main jets along and just move the E-clips on the jet needles.
The mixture screws are a fine tuning adjustment.
If you cant get Rich or lean enough with nthe mixture screws.
Then its time to change the range by moving the E-clips and then adjust the mixture screws again, while in a different range..
E-clip down a notch raises the jet needle and gives a Richer Fuel Mixture when the Main jets kicks in, 1500 to 2500 RPM's.
The Pilot jet is Fine if its Ideling Well.
Also check the plugs for color to see if the mixture is Rich (Black Plug)
or Lean (Gray or White Plug).

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william joseph stack


I specialize in Virago carburetors. Internal parts sizes, Needle and jet sizes for each and every year and model. Hitachi and Mikuni. I also can give tech support and Tech Support for carburetor problems and issues. Carburetor tuning and syncronization. Carbburetor rejetting and dynojet installations for engine modifications. I know every needle and jet size for every Virago made. I have done over50 Virago carb Salesand Rebuilds in 2012. I have over 50 sets ofVirago carbs in stockright now. I Build, Ride and Breath Virago. I have both the 1983 Midnight Virago's. The XV750MK and the XV920MK. 1 of my 1981 XV750H is is Premier Cycles, Billy Joel's Bike Museum.... I am an Honest and Fair man. I am also a Finicky Perfectionist withmy carb work. Ihave all the obsolete hardto find carb parts. I have new diaphragms, new floats, I have the float level setting down to an art. I have fabricated transparent bowls for both version 1 and version 2 carburetors.


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