06' smr510: Don't understand carbs, but think i/it messed my bike up.

So when I put the bike back together, and after addressing some electrical gremlins and fitment issues, she started right up first try last week (hadn't ran since sept.) so I've been taking it slow, just doing laps around the house and up and down the street to monitor it closely after rebuild and before her 'first' oil change at 100 mi...
Yesterday I saw this purple (a/f ratio knob I presume) knob with the numbers 1-4 etched into it had vibrated out of it's home on the bottom side of the carb and was resting with it's head touching the top of the bottom end while the engine continued to run. I didn't know how far to screw it back in but I turned it all the way in until it was finger tight.
Now that was obviously too much because it shut off a minute or two later in my backyard and will no longer fire up. Now I have adjusted it all the way in, all the way out, and everywhere in between it seems... I cannot get it to even try to fire (backfire or whatever) the starter just spins up when I press the button but nothing else...
Suggestions?
should I take the carb out of the bike and try to clean it?
it was running perfect until I screwed it in and it stopped running....
also, should I add a dab of Loctite to that purple knob so it doesn't rattle loose again or is there a better way to keep it in place while still being able to turn it when needed?
I'd hate to have to pay somebody to look at the bike when I kind of already know what's wrong with it, just not how to go about fixing it!

Thanks in advance for any replies and sorry I wrote so much for you to read. haha

regards, Tyler

Tyler-

It sounds like an after-market fuel screw (aka fuel needle, needle screw... not to be confused with the float needle). Fuel screws usually need to have an o-ring and a spring with it (the spring provides tension to help keep it from backing out), sometimes a tiny washer- and order of assembly matters. Check your parts or workshop manual.

The fuel screw controls the mixture from idle to 1/8 throttle (maybe a bit more).

The "normal" setting is usually 1-1/4 to 2-1/4 turns out from finger tight... when you have all the required hardware in there. Anything outside this range can indicate the need for a pilot jet change sometimes. The numbers on yours are just for handy reference and used for adjustment (out=richer, in=leaner ...for fuel screws)

The pin end is sorta delicate.

good luck.

Thanks for the info Trench.
When I found the fuel screw all the way out, the bike was idling real high, up around 2700rpm. I adjusted the idle down before noticing the screw loose. So now she's all out of wack but at least I have somewhere to start!

For what it's worth, the knob is green. I don't know what possessed me to say it was purple lol