SETTING IDLE MIXTURE WITH A LEAK DOWN TESTER


1. Remove return hose from barrel valve outlet and install cap on outlet fitting.  Also cap off any other bypasses such as hi-speeds and idle bypasses.

2. Set throttle body blade gap(s) with a feeler’s gauge.  As a starting point, a Flying Toilet should be set to .012-.015 and a Terminator to .008-.010.  These recommendations are for single throttle body applications.  If you have a dual throttle body setup set the blade gaps to .006-.008 for Flying Toilets and .004-.005 for Terminators.

3. Position fuel shutoff lever into the fully OFF position.

4. Remove inlet hose and install hose from leak down tester on inlet fitting.

5. Turn regulator adjusting knob counter-clockwise until it stops then connect air supply.

6. Open fuel shutoff lever into the fully ON position.

7. Adjust knob on the regulator clockwise until the gauge on the left reads 100 psi. 

8. Note the gauge on the right as it is the “leak down percentage”.  As a starting point the leak down percentage should be at 25% in most systems*.

9. Remove leak down tester hose from inlet fitting and all caps from return fittings and reinstall system hoses.

From this point the engine should start, idle and RPM cleanly without hesitation. If the idle is a little low when first running the engine open your blade gap slightly.  Conversely, if the idle is a little too fast close your blade gap slightly. 

If more than a small blade gap adjustment is needed you may need to alter your leak down percentage slightly.  Lengthening the barrel valve turnbuckle will lean the mixture; raising the RPM.  Shortening the barrel valve turnbuckle will richen the mixture; lowering RPM.  Only small changes will need to be made to the blade gap and/or idle mixture. 

If you need to move the blade gap more than a couple thousandths or the idle mixture more than a few percentage please contact a KillerRONS.COM technician for further guidance. 

When making these adjustments shoot for around 1700-1800 RPM in park or neutral with a warm engine (150 degrees water temperature minimum).  Remember it will drop 300-500 RPM when put into gear with a torque converter equipped vehicle.  Mechanically injected cars don’t like to idle much below 1,000-1,100 RPM in gear.  Most users utilize 1,300-1,400 RPM for best results.

Once you have made the above changes it is a good idea to redo the leak down procedure and note the final blade gap and barrel valve percentage settings for your records.


*The above settings are for Ron’s Fuel Injection leak down testers only.  Other brand testers will vary slightly.