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post #1 of 11 (permalink) Old 05-31-2016, 10:33 PM Thread Starter
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jetting advice

i have a hyper charger coming in a few days, my bike is a 650 with semi gutted stock mufflers what i'v been reading is to use 120 mikuni jets and shim the needle with 2 #4 sae washers and 3 to 3.5 turns on pms screws using the stock pilot jet is anyone using this set up, what i'm not understanding is some of the jetting advice is showing some bikes using pressurized bowls and some using non pressurized bowls does anyone know the performance difference between pressurized and non pressurized and if using non pressurized do you just leave the bowl vent alone and that's it? any and all advice is welcome from anyone who done this mod

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post #2 of 11 (permalink) Old 06-01-2016, 06:10 PM
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I'm not 100% sure on the 650, but I do not believe they are pressurized if they have a vent hose. The vent allows it to maintain atmospheric pressure...which would not be pressurized.

120 Mikuni mains sound about right and 5th groove on the Dynojet needles...I think the kit comes with Dynojet stuff....at least they used to. At least that's what I've heard. Please verify for sure.

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post #3 of 11 (permalink) Old 06-01-2016, 07:09 PM Thread Starter
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Originally Posted by Sick Mick View Post
I'm not 100% sure on the 650, but I do not believe they are pressurized if they have a vent hose. The vent allows it to maintain atmospheric pressure...which would not be pressurized.

120 Mikuni mains sound about right and 5th groove on the Dynojet needles...I think the kit comes with Dynojet stuff....at least they used to. At least that's what I've heard. Please verify for sure.
i bought the charger used without a jet kit, buying a dyno jet kit for 80.00 and using 20.00 worth of the items in it just doesn't make sense, i ordered two 120 mikunie's i think i'll try just shimming the needle with those jets and go from there i think at most i may need two larger or smaller jets if the 120s aren't right either way i'll only be spending half of what a dyno jet kit costs, i'm hoping 3 turns on the pms screws will be the same as installing a larger pilot jet and tuning the screw 1- 1/2 turns which is what the dyno kit suggest's for a charger install, i'm real fussy so what ever it takes to get the best milage and performance i'm gonna do, if i need a jet kit to get it perfect i guess i'm buying a jet kit, a lot of guys tune their bikes overly rich to stop exhaust popping on deceleration, and when your overly rich, top end and milage suffer. did you ever hear nascar racers on deceleration they pop because their tuned perfect for the best top end and torque, listen to racing bikes they pop like crazy too when decelerating, sometimes i'll just hold the throttle open just a crack when decelerating to stop the exhaust pop, it's mostly when you chop it that causes popping especially if you were really pulling before you chop it making the engine go from extremely rich to lean in an instant

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Last edited by pauli466; 06-01-2016 at 07:28 PM.
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post #4 of 11 (permalink) Old 06-01-2016, 07:51 PM
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Hypercharger Install* - 650 CCND i dont know if you've seen this or not.i dont know the stock size of the pilot jet, but the link calls for two shims on the needles and set the pms at 3.5 turns out. the 120 mikuni is the same as the 128 dyno and the 128 dyno is the largest recommended so you will probably be ok at full throttle.i can induce popping on decell by turning the screws in about an eighth turn so it dont take much.i think you would be closer adding shims rather than upping the pilot jet, because the needle acts on vacumn pressure caused by the action of your right wrist and the pilot jet acts by a steady increase in throttle.
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post #5 of 11 (permalink) Old 06-01-2016, 08:06 PM Thread Starter
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Hypercharger Install* - 650 CCND i dont know if you've seen this or not.i dont know the stock size of the pilot jet, but the link calls for two shims on the needles and set the pms at 3.5 turns out. the 120 mikuni is the same as the 128 dyno and the 128 dyno is the largest recommended so you will probably be ok at full throttle.i can induce popping on decell by turning the screws in about an eighth turn so it dont take much.i think you would be closer adding shims rather than upping the pilot jet, because the needle acts on vacumn pressure caused by the action of your right wrist and the pilot jet acts by a steady increase in throttle.
the hardest part to get perfect is the transition from pilot to main there's a throttle position usually about 1/3 where the transition occur's i heard of making thin washers from aluminum cans to really get it dialed in perfect, kinda like making micro adjustments

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post #6 of 11 (permalink) Old 06-01-2016, 08:22 PM
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is the ram air effect of the hyperch. greater than atmosp
heric pressure.the recommended main is 128 how much of an increase is that over stock.. what is a stock main size
?the needle circuit is between the pilot and main circuits. you can buy shims from radio shack .
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post #7 of 11 (permalink) Old 06-01-2016, 08:53 PM Thread Starter
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Originally Posted by nick57 View Post
is the ram air effect of the hyperch. greater than atmosp
heric pressure.the recommended main is 128 how much of an increase is that over stock.. what is a stock main size
?the needle circuit is between the pilot and main circuits. you can buy shims from radio shack .
already got a bunch of #4 sae stainless washers and the stock main jet is a mikuni #90 small round jet. the stock pilot fuel jet is a mikuni #20 and pilot air jet is a mikuni #100

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post #8 of 11 (permalink) Old 06-01-2016, 10:43 PM
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Yeah...I've never bought a kit....ever. Ridiculous what they charge for a bunch of crap you have to throw away. The shimming on the Dynojet needles is quite a bit different than what you'd need with the stock needles...which are better IMO.

Just get it close and go have the AFR checked at idle, 1/2 throttle and 3/4 throttle. That'll tell ya where the jets/shims need to be....less guessing or messing around that way.

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Last edited by Sick Mick; 06-02-2016 at 09:44 AM.
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post #9 of 11 (permalink) Old 06-02-2016, 08:44 AM
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I didn't know anything about doing the jets in my carbs when I bought my bike. So I went with a kit. I got mine on ebay and did pay more for it than I maybe should have. But having no experience I found this the best choice.

I did get jets I didn't use, as they included a couple different sizes. But I got good instructions and was able to do the change with no problems. I also adjusted the main needles easily using the instructions. I got washers but my needles were adjustable so didn't need those either.

I have to say, the jets did wonders for the bike both in starting and running. So even though I may have paid more than I needed too at $56, it was worth it to me.
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post #10 of 11 (permalink) Old 06-02-2016, 05:21 PM Thread Starter
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Originally Posted by smokindawg View Post
I didn't know anything about doing the jets in my carbs when I bought my bike. So I went with a kit. I got mine on ebay and did pay more for it than I maybe should have. But having no experience I found this the best choice.

I did get jets I didn't use, as they included a couple different sizes. But I got good instructions and was able to do the change with no problems. I also adjusted the main needles easily using the instructions. I got washers but my needles were adjustable so didn't need those either.

I have to say, the jets did wonders for the bike both in starting and running. So even though I may have paid more than I needed too at $56, it was worth it to me.
was it the sigma kit?

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