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Why Fuel Injection?

 FUEL INJECTION BASICS

One of the main goals of this website is to put valuable information for tuning mechanical fuel injection at the fingertips of the user and, at the same time, help the potential buyer feel more comfortable and informed before he or she makes a decision. 

Please take the time to read over the below information and if at any time you have questions please call and it will be put it in "plain english".  All of the below adjustments are pre-set from the manufacturer so new users need not be concerned or intimidated.

One of the most basic adjustments in a mechanical fuel injection system often overlooked by a new user is the barrel valve adjustment (idle mixture).  As discussed above, an incorrect barrel valve adjustment can result in excessive fuel consumption and poor performance, especially early in the run. 

Idle speed is set by the amount of air shown to the engine dictated by the IDLE ADJUSTMENT SCREW.  Newer systems such as the one pictured have an adjustment screw on each side of the throttle body.  For initial adjustments, it is best to back one off and focus on the side that is most easily accessible with the engine running.  This throttle body has been set initially at .010 (call for recommendations for your system); which has been measured with a feeler's guage between the throttle body bore and it's respective blade (see below photo).  On this Terminator throttle body, you will notice the SHAFT TIE ROD (one on each side), this is used to phase the two throttle shafts so they work in unison.  This, more than likely, has already been done from the "factory" and shouldn't be adjusted.  In other words, the feeler's guage would read .010 in all four bores in the above photo.  On a Toilet throttle body there is only a single throttle shaft so these shaft tie rods are not utilized.

The BARREL VALVE TURNBUCKLE is used to set/adjust the idle mixture.  If you look closely at the above photo you will notice the index mark on the SPOOL is oriented just left of "straight up vertical".  To adjust the idle mixture, the user should loosen the two jam nuts on the barrel valve turnbuckle to allow the tie rod to be adjusted easily.  To lean the mixture the turnbuckle would be lengthened which rotates the spool clockwise toward straight up vertical or 12:00.  To richen the mixture, the turnbuckle needs to shortened which rotates the spool counterclockwise.

Above you will see the spool removed from the barrel valve.  Notice the notch begins very shallow and progresses deeper.  This is the "gate" that determines how much fuel is allowed to pass through to the injectors at any given throttle position.  The Shallow Portion of Notch is the area that utilized at idle to let a small amount of fuel past.  As this spool is rotated toward wide open throttle, the Deep Portion of Notch comes into play and allows the fuel to flow through virtually unobstructed.

LEAKING THE BARREL VALVE
There are a couple ways of  monitoring/setting the barrel valve percentage (idle mixture).  We feel that the MOST ACCURATE way to do this is with a leakdown tester which most racer's have in their toolbox.  If you do not have this piece and plan on running injection for the years to come, Ron's makes an affordable unit that can be purchased on this site.  Below you will find step-by-step instructions for leaking down your barrel valve and the tolerances are generic.  Call for recommended settings for your specific combination.

Cap the return side of the barrel valve so no air can escape.

Install leakdown tester to the barrel valve inlet with modified line.

Adjust guage(s) to 100 psi.

Set blade gap to recommended setting with feeler's guage (call for recommendations if you are unsure).  This is easily done initially by using only one BLADE ADJUSTMENT SCREW and backing the others off.  Later all remaining screws can be brought to desired blade setting.  A baseline setting is around .012-.015 for a single blade throttle body (Toilet) and .009-.012 with the two or four hole unit (Terminator or T2).

All of the above should be done with the fuel shut-off in the OFF position.  Once you are ready to take a measurement with 100 psi move the shut-off into the ON position and note the readings.  The guage below reads 30% leakdown (100-70=30).

Note:  This is 30% is an example; call for recommendations for your specific combination.

Refer back to the above BARREL VALVE TURNBUCKLE paragraph for adjusting this percentage to the desired value.  One of the most critical adjustments in the injection system is the orientation of the barrel valve shaft (spool) in relation to the fuel gallery at idle, part throttle and finally at WOT.  Incorrect adjustments in this area at idle can lead to excessive fuel consumption and oil contamination.  Those two symptoms are believed by many to be inherent with injection and that is just not the case!