Other factors aside, the quality of starting, idle, off-idle, and a little up the rev range are largely determined by the pilot jet and fuel screw in conjunction with a correct idle speed adjuster. A jetting kit is not needed to set the pilot jet and fuel screw correctly. It's basic info and basic adjustments
Given a choice of certain main jet and needle, the pilot jet size is determined by the procedure in the manual to set the fuel screw. The following is from the '08 manual. The procedure is simpler to do than it is to write out
CARBURETOR – ADJUST IDLING *
Idling adjustment of the carburetor strongly affects the engine’s starting behavior. That is, an engine whose idling speed is adjusted correctly will be easier to start than one whose idling speed has not been adjusted correctly.
The idle speed is controlled by means of the adjusting wheel (1) and the mixture control screw (2). The adjusting wheel is used to adjust the basic setting of the slide. The mixture control screw is used to control the idle mixture which arrives at the engine by way of the idle system. Clockwise turning reduces the fuel quantity (lean mixture), counterclockwise turning increases the fuel quantity (rich mixture).
To adjust idling correctly, proceed as follows:
1 Turn in mixture control screw (2) up to the stop, and turn it back out
to the basic position (see technical date-engine)
2 Warm up the engine
3 Use the adjusting wheel (1) to set the normal idle speed (1400 - 1500
rpm).
4 Turn mixture control screw (2) slowly clockwise until idling speed
starts to decrease. Memorize this position, and turn mixture control screw slowly counterclockwise until the idling speed decreases again. Adjust the point of the highest idling speed between these two posi- tions. If, in the course of this procedure, the speed undergoes a rela- tively high increase, reduce the idle speed to a normal level and repeat the procedure specified in 4. Serious competitive racers will choose a setting approx. 1/4 turn (clockwise) leaner than this ideal value because their engine will heat up more when used in competitions.
NOTE: If you fail to obtain a satisfying result by following the procedure described above, an incorrectly dimensioned idling nozzle may be the cause. If:
a) the mixture control screw has been screwed in up to the stop without causing any change in rotational speed, a smal- ler idling jet has to be installed;
b) the engine dies when the mixture control screw is still open by 2 turns, a larger idling jet needs to be selected.
Naturally, in cases of jet changes, you have to start your adjusting work from the beginning.
In short you want the pilot jet that allows you to set the correct idle RPM within 0 and 2 turns out on the fuel screw. The position you want the fuel screw in is where you get the best combustion, the best vacuum - in other words where you need the least action of the idle screw to get the correct RPM. You kind of feel the right point.
In yet other words, set the correct idle on a warm bike and adjust the fuel screw. What you want is to feel it idle a bit worse when you screw the fuel screw in a turn or so, best in the middle, and a bit worse when you screw the fuel screw a turn OUT or so. If you can't get it to idle well at any screw position within approx 0-2 turns out, you may want a bigger pilot jet. If you can't get it to stumble or stall at all if you screw it all the way in, you need a smaller pilot jet.
And of course get a good o-ring in there, only one of them
Again: The procedure is harder to describe than it is to perform
That you didn't need choke to start at first, and that it then died when warm strongly indicates that you were too rich on the pilot. That the fuel screw was all the way out and the o-ring situation was goofy kind of obscures if the jet itself was good for you or not. So I'd advise first fixing the oring situation and then seeing what happens if you start screwing the fuel screw in - adjusting the idle speed with the idle adjuster as you go along as idle will tend to jump around a bit when the fuel screw is adjusted. If it stays like that - no choke needed cold, dies when warm - as you turn the fuel screw in, that indicates you want the next smaller pilot jet.
Kinda funny that mr. expert here makes no mention of setting the fuel screw correctly. I'm sure that you'd want the pilot and idle circuits in good shape whatever you do.
