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Author Topic: When to upjet to a larger pilot jet  (Read 9564 times)

Kenho21

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When to upjet to a larger pilot jet
« on: May 26, 2012, 05:51:03 PM »
70cc kit, open aide filter and performance exhaust, think I should upjet the pilot? Have to turn the screw pretty far out to get a decent idle...
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wordslinger

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Re: When to upjet to a larger pilot jet
« Reply #1 on: May 26, 2012, 09:11:28 PM »
...have you increased main jet??

..you probably need to raise your needle, bro...

..and with the oem carb, that requires some modifications to the needle retaining clip...and the needle's head...
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Kenho21

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Re: When to upjet to a larger pilot jet
« Reply #2 on: May 26, 2012, 10:30:23 PM »
Yea, the main jet is 105 right now I believe, probably gonna drop it down to a 95-100 though, 105 is rich.

You mean putting a washer around the needle to raise it a little? I did that before but then took it off because I didn't notice any difference.

What kinda mods are you talking about with the needle and the retaining clip?
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wordslinger

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Re: When to upjet to a larger pilot jet
« Reply #3 on: May 26, 2012, 10:54:18 PM »
..i dunno, kenho...but i believe that just a pipe without more air in is sorta counter-productive...
..you up-jetted for the pipe, but the oem airbox can only suck just so much air...

..that's why your scoot is running rich...

...in my experience, replacing the airbox has been the best mod ever on my 4t engines...
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zombie

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Re: When to upjet to a larger pilot jet
« Reply #4 on: May 26, 2012, 11:44:04 PM »
The Pilot does need to be changed depending on the set up. Every engine I have built for better flow rate is the reason I say this. The pilot is as important as the main in most cases. If you are more than 1 full turn from OEM mix screw setting you need to change the pilot. You may have the correct ratio of fuel/air but not the right amount.
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wordslinger

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Re: When to upjet to a larger pilot jet
« Reply #5 on: May 26, 2012, 11:45:59 PM »
...4t oem pilot jet screw is 2.5 turns out...
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Kenho21

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Re: When to upjet to a larger pilot jet
« Reply #6 on: May 27, 2012, 01:41:29 AM »
I do have free flow Uni air filter, so upjetting was definitely necessary but not to a 105, my neighbor made me a bunch of sizes and I lost the envelope containing all the others so I'm stuck right not with the 105 until my new ones arrive.

@zombie- Thanks for the tip about being 1 turn out, I never knew that.

@wordslinger- So what about adjusting the needle?

Would adjusting the needle cancel out installing a new pilot or vice versa?
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wordslinger

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Re: When to upjet to a larger pilot jet
« Reply #7 on: May 27, 2012, 02:03:59 AM »
Quote from: wordslinger on May 26, 2012, 11:45:59 PM
...4t oem pilot jet screw is 2.5 turns out...
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Kenho21

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Re: When to upjet to a larger pilot jet
« Reply #8 on: May 27, 2012, 02:30:36 AM »
I meant 1 turn away from factory OEM setting, so 3 1/2 turns I guess
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zombie

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Re: When to upjet to a larger pilot jet
« Reply #9 on: May 27, 2012, 03:24:21 AM »
Would adjusting the needle cancel out installing a new pilot or vice versa?

Yes. The needle controls bleed from the main. If you are too rich lowering the needle fixes it or lean raise the needle to get more fuel. That is a rougher setting. The correct jet is always best.Some times you just get stuck between, and needles make the difference.
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Kenho21

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Re: When to upjet to a larger pilot jet
« Reply #10 on: May 27, 2012, 06:06:36 AM »
Ohhhhh, thanks for the clarification, did not know that
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wordslinger

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Re: When to upjet to a larger pilot jet
« Reply #11 on: May 28, 2012, 08:02:34 PM »
..like z said, itsa good mix throughout throttle that makes best performance..

..on my 08 a50, i always ran best with my needle reised .025"..with k&n, and modified exhaust...

..they all different tho...

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Kenho21

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Re: When to upjet to a larger pilot jet
« Reply #12 on: May 28, 2012, 10:20:12 PM »
And pretty much the only way to figure it out is with plug chops I'm assuming? ...pain in the ass
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zombie

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Re: When to upjet to a larger pilot jet
« Reply #13 on: May 28, 2012, 10:32:36 PM »
Plug chops are the best way but you get an "ear" for jetting in time. The best way to go is get the idle circuit at 2.5 turn using the proper jet, and work on the mid/wot jetting after. That give you time to seat the rings too.
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wordslinger

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Re: When to upjet to a larger pilot jet
« Reply #14 on: May 29, 2012, 12:51:28 AM »
..after a while, when you know your scoot, you do indeed get that ear...
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