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Discussion Starter · #1 ·
Can you get an accurate reading of the jetting while just revving the quad without a load? (ie: in neutral)?

Also, to check the idle mixture, could you just let it idle for a while and then check the plug? How long would it need to run?

And can you do that same thing for the other parts of the rpm range? Like rev it to half throttle for a few seconds and then read the plug?

Because I got ahead of myself and found that I still do have a jetting problem, and I just don't know enough about what to listen for and what different a/f ratios will do. I still have a 3/4-full backfire/pop/stumble.

It just seems like I keep messing with the jetting and not getting any luck...
 

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Discussion Starter · #2 ·
Here is line of thoughts I had after puting some thought into this:

Fuel screws are at 2.5 turns, and that is supposed to be just about right. Plus my idle is great.
Pilots are 25's which seems to be what most people are running and my 1/4-1/2 throttle is fine.
Mains are 160/165, which mike at CSR recommended to me and are definitely not too small when I look at what others are using.

So that leaves my needles as the last variable. I'm running stock needles with the clips in the middle position. I think I'm going to bite the bullet and buy a GYTR jet kit just so I can get the needles. Mike told me that he's never been able to get a modded engine running right on stock needles.

And for reference, my mods are: ported carb boots, trimmed float bowl stops, cleartube tuned, stock replacement K&N with no lid (I used screws to secure it), all with just a stock pipe without the spark arrestor.
 

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I have a hard time questioning Mike but if you have a stumble at 3/4 to full throttle thats the mains, needle position is for up to 3/4 or so.

As for wanting to do jetting tests in neutral, I don't think it will work, you'll need a longer duration test than your going to be willing to do in neutral and I'd think the fact that there's no load would have an effect.
 

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Discussion Starter · #6 ·
Yeah, I've been looking high and low for just the needles and I can't find them anywhere. There was a guy on ebay selling GYTR needles for YFZ's and I emailed him but never got a response.
 

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Discussion Starter · #7 ·
firstraptor said:
I have a hard time questioning Mike but if you have a stumble at 3/4 to full throttle thats the mains, needle position is for up to 3/4 or so.

As for wanting to do jetting tests in neutral, I don't think it will work, you'll need a longer duration test than your going to be willing to do in neutral and I'd think the fact that there's no load would have an effect.
But don't you think 160/165 is sufficient? I can't see that combo being too small.
 

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pewterpecker said:
But don't you think 160/165 is sufficient?
sure would think so,

The stock needles were one of the first things to go away, don't remember much about them.

I'll check my parts, if I have something other than the stock your welcome to try them. Won't be till the weekend before I can look.
 

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Discussion Starter · #10 ·
Well, I dropped my clips down one notch and that evened out the powerband a bit. I'm still getting a pop from 1/2 throttle up but it's not as bad. Plus it was only 45 degrees in my shop.

I think I need to turn my mixture screws down a bit though. It revs kinda slow to 1/4 throttle and then it suddenly "wakes up" and the revs take off. Does that mean I need to turn my screws in a little?

Also, if I throw the lid back on it revs fine.
 

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fuel screw out will richen the mixture.
 
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