A brief explanation on your turbo charged mechanical fuel injection system:


You must put your mind in the thought process that you are not putting fuel in the engine but you are restricting the fuel going back to the fuel tank.


When changing the Main pill or 4 valve you will see that the holes are sized 130 to 170 ranges. (or so) since this is the main fuel jet and restricts the fuel returning to the tank, whatever doesnít go through that jet back into the fuel tank goes into the motor.  So 130 would be the richest setting and 170 would be the leanest.


When working with the A Valve or 2 jet valve you are using a diaphragm valve also to restrict the fuel that is being returned to the tank.  By adding boost pressure to the dry side of the diaphragm or through the Mikuni main jet you are pushing against the fuel being returned to the tank. This action forces more fuel to the engine richening the mixture. 


As boost pressure fluctuates the air on top of the diaphragm also changes richening and leaning the fuel curve with boost curve.  The jets you have here are AIR jets and not fuel jets.  The larger the Mikuni main jet is the more boost pressure will be allowed against the diaphragm this will richen the mixture.  Bigger jets, richer fuel mixture and vice-versa.


Once the system is set up properly it will require little change.


If you find yourself in a situation where you cannot make boost pressure, or the bike wonít run like it did last time out and you havenít changed anything in the fuel system. DO NOT MAKE BIG CHANGES in the jetting or increase the limit on the two step. There is something else wrong.


Fuel injection doesnít know or care what your compression ratio is or any other part of your combination. The injection is squirting a predetermined amount of fuel, if there is a mechanical problem with your engine or turbo charger it is still going to squirt.  It is most important to keep your engine at its top mechanical condition for the system to work its very best. 


When your motor starts getting tired you will be able to tell. Donít over compensate with excessive timing, high rev limits and unsafe lean fuel conditions.


Keep the fuel system clean.


Donít let alcohol set in the system for longer than a couple of days it will eat your aluminum fittings and clog the system up. I take my system completely apart, blow out the hoses and take apart the jet cans, then liberally use WD-40 on all the parts.  DO NOT TAKE APART THE FUEL PUMP, it runs on very very tight tolerance. Blow it out and fill with WD-40 or a light machine oil, same with the boost compensator donít take it apart just lightly blow it out on the diaphragm side, and then lubricate the piston in the 2 jet valve.


After a period of time alcohol will attack the compensator diaphragm and it will stiffen, the result will be a overly rich or lean mixture, this should be a annual maintenance item.


Always use fresh fuel.


If your bike misfires going down track fuel quality should be the first suspect. Donít buy more fuel at one time than you can use up in a month or two, it will go bad.


Properly maintained the system will last for years without the need of replacement of anything except the compensator diaphragm.



I hope this helps.