I know most opinions here say order original mikuni parts rather than aftermarket. I’m wondering if any aftermarket parts are passable. Looking at float needle and seats. Niche offers a “quality” replacement for about $8 whereby Rocky Mtn or partzilla’s oem are at $23 plus the usual $10-$20 in shipping. I’ll obviously bite the bullet if the consensus in this instance suggests OEM is the only reliable option. Appreciate some opinions. 

Niche sells genuine Mikuni as well...  usually much cheaper than OEM...  sometimes 1/3rd of Yamaha price

Other than that, aftermarket probably okay...  I have seen a couple aftermarket "rubber tip" needles fail quickly though.  Metal ones seem fine. 

Last Monday I ordered a float valve and seat from Niche, and it was supposed to be here by now, but it's a little delayed. My understanding was that it is OEM, and I'll let you know when I get it. It was under $8 plus shipping.

My carb had started overflowing, but I really think it was because the cheap petcock I put on had stopped turning off completely. Since I put on a Yamaha petcock that actually shuts off, it hasn't been overflowing anymore.

Yes, you must shut off petcock on these bikes.  Lucky you didn't have the engine flood with fuel.

I agree MarkT. I've always shut off the petcock on every motorcycle I've owned when I stop. What happened was after I put the cheap petcock on, it was shutting off completely, and I knew this because I removed the tank with it full of gas with the petcock off.

Then a few weeks later I came out one morning and smelled gas in the garage. Even though the petcock was shut off, it was still allowing a small flow. At that point I began putting needle-nose vice grips on the fuel line to make sure it was shut off, until I received the genuine Yamaha petcock.

Because the overflow was working, the engine never filled up with gas, but I actually feel lucky that I didn't end up with the garage fire. I left an appropriate one star review on the Amazon site where I ordered the cheap petcock, warning that it would not shut off after a few weeks.

If you search for a Yamaha ATV petcock, and it costs from $8 to $15 and is made in China, just pass. In fact some get sneaky,... they have almost the OEM part number, but they have an extra 1 on it, or a minor difference.

In theory [wonderful thing theory till it doesn't work] you shouldn't need to turn it off--until a fault develops--then its too late. You can get vacuum [auto shut off] petcock with the same screw hole spacing that a lot of quads run. Not genuine for originality of course. On both my JT1's i used a vacuum tap [petcock] off Yamaha V50 or V90 scooters & worked as they should--no more worries.

I shut my gas off and let them run the bowl dry when I put them away for any length of time. I often wondered if that’s a bad practice because I’m sure that’s a lean condition as it gives its final revs.

I just let my 360 run dry yesterday & it didn't rev up but just started faltering so i choked the last bit out of it with a bit of a rev, only guessing 3 grand up & down twice & gone. Sure way would be to just back off the speed sidle screw if it gets too high. But to take off reving realy it'd have to be way over rich idling to do that----& just saying, as nothing worth watching on tv tonight.
Yes our rotten 91 octane fuel had gone off & the oil was sitting in the bottom of the bowl & smoked the neighbors out. Mind you i think that mix was some 5/30 synthetic car or 4 stroke bike oil so maybe doesn't stay mixed for long. Smells fast lol.

I was going to post here if the inexpensive Niche needle valve and seat were OEM, but they just haven't shown up yet. It seems like they've gotten lost in the mail. If they show up I will post a picture and let you know if they are OEM. Meanwhile, my 50-year old ones are still working fine, since I put the new working petcock on.

Niche does sell Mikuni but also might sell aftermarket.  Their Mikuni valves are a fraction of the Yamaha price usually.