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This is probably a stupid question but jetting has always messed with me and have been scared to try it cause I feel like if I get one thing wrong and don't put enough gas into my motor it is gonna seize it up or something. But I wanna try it. So say a #50 pilot is a bigger jet (richer) than a #40. Right? Just wanna make sure. And my bike runs fine it has good power and everything but when I'm cruising low in the rpm's and fully open it up as fast as I can it wants to just die and sounds like bwoooooooooop and won't get back up. I can baby it and it will be fine but I want it to be perfect. That's usually a lean pilot jet. Correct? And also I took my bike to get jetted and he said the main jet was a little rich so he leaned it out. But now I am going to have a lean pilot jet and a lean main jet. And is that not a little weird to have everything that LEAN?
Also what if it's has been changed before. Are their numbers on the jets that will tell me what's in it? I'm planning on buying two jets lower then what's in it but idek what's in it. Like I said, carbs have always been a big headache but I'm tired of giving somebody 40$ to change out a 1$ part. And I like to be able to do as much as I can to a bike. Also what makes a bike have that Crisp/raspy/crackling/popping noise? Jetting? You hear all these two strokes and they have a ring ding ding sing ding noise but then you hear that one that sounds mean, NOT LOUD, but mean and cracky. I'm not looking for the no silencer noise. Also should I run race gas? I know that will mess my jetting up but I will put it in before I buy these jets. It's not bored, it's not ported, it's not for any reeds or nothing. Stock pipe and an FMF shorty. That's it. Is it worth the race gas? Sorry for the long post but I want my bike to run clean and right now I just feel like I'm torturing it riding like this. Although the jetting is so little off where if somebody else rode it they would not notice it, I still like my bike to just feel comfortable and new when I'm on it. There is a link attached that shows the sound I am talking about. https://m.youtube.com/watch?v=w5G7s3dKu1I

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Jetting is dependent on your location altitude, temperature and to some degree humidity. Post back where you ride, the elevation and the hottest and coolest temps throughout the day and I can offer a couple of suggestions. Also need to know year, and what carb is on your YZ...Mikuni and Keihin carbs have different jets and numbering systems. The jets will have numbers stamped into them...small and hard to read but they're there.

 All this assuming everything is mechanically sound with the motor, clean air filter, silencer is packed correctly. Trying to jet a motor with other mechanical issues or air leaks is just chasing ghosts.

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The first thing I would get is a manual.  They are full of good information.   I wouldn't buy anything else until I had set the float to factory specs using their method.  Here is where you might have to buy a "tool" if you can't use epoxy.  I would be tired of paying others too.  Yours should have a Mikuni carburetor and the jets have been available for that one as far back and the Amalgamated Carburetor Company.  

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It's great you're going to learn to jet your bike. It's difficult for a shop to get right because you have to ride it a bit and some of it is iterative.
All your jets are marked. Learn what's stock for your year engine. Then, start compensating for altitude, change in premix ratio, differences in pipes, etc...

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Sounds like your issue is when you are "cruising at low rpms" (maybe 1/8-1/4 throttle...then, you "fully open it up as fast as you can" (3/4-WOT) and it "wants to die".
Look to see what needle and main jet you have in it. Where's the needle clip?

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