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Discussion Starter · #1 ·
Good morning to all of you ! (it's the morning here in france),

Forst off all I'd like to thank all of you for the wonderfull anf highly appreciated support.
I own an YFZ since 3 months now. I've never made motorbike nor quad before and was a bit scared by all the mechanic that I would have to do to make that quad run at is best without spending a fortune with my dealer.
I've been reading all the posts (quite all the posts !) of this amazing forum and learned a lot.
Last week I've tried to jet my quad (after taking off the baffle and the airbox lid).
And you know what ???
:rock THIS IS A GREAT SUCCESS AT THE FIRST ATTEMPT !!!
170 main, 45 pilot, stock needle on 5th clip and airscrew at 2.5. (used Daddog recommendations found on his marvellous website : yes Daddog you're the nicest mas I've ever read !! Sharing your knowledge like that is really helpfull for rookies like me).
Now my quad runs really fine.
But I still got two question :
- what is the needle and the clip position for ? how does it work ?
- what is the air screw for ? how does it work ?
I would like to understand what I've done.
I've seen no post explaining that : perhaps I haven't searched enough, and it that case I accept being flamed ! but please could you explain me ?

Oh, one more thing, that seems strange to me : my stock needle has 7 clips ! strange when all of you say it has 6, no ?

Thank you for your responses, and thank's again for all the other posts !

Nicolas, a lonesome french rider, lol !
(for the ones of you how knows this french competition, I will race my first ENDURO DU TOUQUET in february, wish me a good luck !)
 

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Nicolas, let me be the first to congratulate you on your succesfull re-jet.
The needle is tapered meaning it goes from thin on the tip to thicker towards the top of the needle. if you lower the clip on the needle, lets say from position 4 to 5, the needle site higher and thus a thinner part of the needle is obstructing the flow of fuel. so the average fuel flow at any given throttle position is higher when you move the clip to a higher (4 to 5) position. i hope this makes sense. look at this illustration to see the dimensions of a needle. http://www.carbparts.com/keihin/needles_tu...r_35_41_jn2.gif.

Quote from carbparts.com "Simply change the clip position, lowering or raising will allow you to make adjustments. A shorter needle will be richer and longer needle will be leaner. The mixture richens when the jet needle is raised and leans when lowered.

As for the "air screw" i am not sure so i won't comment on that.
Hope this helps.

PS When is that awesome beach race you guys have every year scheduled? i saw coverage of that race on the speed channel this year. it was awesome.
 

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Discussion Starter · #3 ·
Thank's a lot Seatec, one thing is now clear now (although I think it's a bit complicated to exactly know the amount of gas you're putting in : the main jet, the pilot jet and now the needle ! pfff !).
Still need an explanation for the air screw..

As for the enduro du touquet, this year it will be on 14th and 15th of february :
the 14th for the quad (238 quads last year runing 3 hours)
the 15th for the dirtbikes (about 1000 to 1100 runing 3 hours too)
Very nice race !

thank's again
 

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You are talking about the Fuel mixture screw in front of the carb. correct?

Here is a brief explaination:

The fuel mixture screw is a low speed fuel adjusting screw. basically is controls the amount of fuel in the mix. turning it in reduces the amount of fuel in the mix, while turning it out increases it. It has the most effect at small throttle openings.

The needle is for midrange performance.....when the slide is is not at full throttle the taper on the needle is in the hole that the main jet pumps fuel out of. The taper on the needle determines how much fuel is allowed to go through that hole. when the throttle is wide open so is the hole the main jet sits in allowing maximum fuel flow from the main jet.

If my explaination has any errors in it...please correct me. thanks
 

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Excellent explanation Merriman especially with the relationship between the needle and main jet during different throttle applications.
 

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Discussion Starter · #8 ·
Merci beaucoup Messieurs !

Nice explanation, the mystery is leaving...
Now, I would like to find a diagram explaining the way the fuel and the air use through the carb, and after that through the engine. With that, I will have understood the way an engine work, and I' ll be able to do more mechanic doing less rubbish.
Anyone has something like that or knows where I can find this ?
 

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I used to know of some websites, but they have slipped my mind as of right now. Best thing I could say is go to www.google.com and search around the internet using various key words. You can also go to www.thumpertalk.com and visit the forums there. They're mainly for Dirt bikes but the basic principles of the YZ dirt bike motors apply to YFZ quad.
 

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Your needle may have 7 clip positions due to where you are. France may have a different regulations so assembely may be different, or Yamaha ran out of needles and used the yz neeedle until they got more.
 
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