In regards to the jetting/adjusting questions, there are a few things that probably need to be pointed out for all the newer members (Like me!) Although I don't always have all the answers, however I'm fairly well read, and am not afraid to research things, ask questions, and give things a go myself.
ANY intake/exhaust mods (eg bigger/smaller exhaust, pod filter, removing collett in airbox, and so on) will require:
1. A replacement jet (high speed jet, not the idle jet unless absolutely necessary).
2. Adjustment of the air/fuel mixture.
Here's how it works:
The Jet controls the flow rate of the fuel, in conjunction with the needle that runs through it.
The bigger the number on the jet, the more fuel it will flow.
If you increase the flow of air through the engine, you MUST increase the amount of fuel going in to it, otherwise the engine will run "Lean" ie; Not enough fuel mixed in with the air, and the engine will run very hot, possibly burning a hole in the piston (you don.t want this).
If the jet is too big, then it's not nearly as dramatic, except the engine will run too "Rich" (too much fuel mixed in with the air), resulting in loss of power, fouling of the sparkplug, and an engine that will run like crap.
Once you've put a bigger jet in, it's time to adjust the air/fuel mixture.
Now remember this: The mixture screw adjusts the amount of air coming in via a very small pilot hole to create a venturi effect. It does NOT adjust the flow of fuel. That is determined by the relationship between the Main (High-speed) Jet and the tapered needle that runs through.
Tighten (do-up) the mixture screw, you let in less air and a leaner mixture will result.
Loosen (undo) the mixture screw, you let in more air and the mixture will become richer.
A perfect mixture (air/fuel ratio) is called Stoichiometric (commonly called Stoich) and is an air/fuel ratio (AFR) of 14.7:1 ie 14 parts air to 1 part fuel, though this is damn near impossible to achieve.
Tuning any engine without an oxygen sensor/exhaust-gas analysis machine is damn hard, with most tuners relying on three things:
1. "Feel" of the engine eg smoothness, pickup (acceleration), sound, vibration etc
2. Temperature ie Leaner mixtures = hotter engine temps, while Richer mixtures = cool running's.
3. Spark-Plug Colour (Ok, Color for you USA scooter-nuts)
For more info on the correct colour of the carbon build-up on your spark-plug, i'm pretty sure I saw a link on here somewhere for an excellent guide....
Just remember, adjusting the mixture screw and riding around for 5 minutes at full throttle will NOT give you an accurate colour-change on your spark-plug. It takes a couple of hundred Kilometres and a wide range of engine load/s rev-ranges, stops, starts, start-ups and shut downs to accurately guage a PROPER colour-change on your spark-plug.
Happy Tuning,
Josh.
