I'm new here, and my 07 S40 is stock, so I'm reading about the mods, and trying to understand them. So the question,
I know about a main jet, and the metering rod (needle), and the low speed idle screw under the brass plug, but what.....and where is the pilot jet ?

Thanks............
Rich

Everyone feel free to correct me...

The pilot jet is where the gas comes thru when you have your throttle turned up to 1/4 of the way [about].

The main jet then comes in [called crossover point] and adds gas as you continue to turn that throttle!

You can get a "blown-out" picture of your carb on the Mukuni site. See Technical section somewhere for link.

Routy wrote on 08/21/09 at 22:06:17:


The jets are inexpensive, and by using new unaltered jets for tuning it makes it easier to know where you are in the tuning process.  
With that said, playing with the jets in the carb is certainly doable, but with these carbs and this engine you must go very slow and easy.  Drilling will likely take you way beyond where you want to go...like 5 steps instead of just one.  I use one of the tiny round diamond files in the minature set.  When filing the pilot jet you want to just barely make contact with the the brass bore and gently turn the file with thumb and forefinger; then test.  If you file until you can see a difference in the bore size of the jet then you have already gone too far.  It is fun to do if you like tinkering on stuff, but just be prepared, it is easy to go to far.