New Product Lines- Moroso & Engler Fuel Injection coming Soon- HILBORN Parts in Stock-The Blower Shop's Largest Dealer
Product Search

    Secure Checkout

    Erratic Idle issues with 8 Stack Hilborn or Other Brand Mechanical injections

    Erratic idle is a gremlin-   very tough to find out why and cure –  Back to basics –

    With Injections , everything has to be very close to perfect or it will not behave , especially at idle –

    Butterflies set to .002”  for Alcohol –  .003” to .004”  for GAS    – DO NOT  subsequently attempt to adjust them to change anything .  Adjusting throttle stops on a mechanical injection in an attempt to adjust the idle is a  No No –  adjust the barrel valve mixture ONLY –  Get a leak down tester made for injection from our web site and  it will save you hours of problems and keep you from milking the oil.

    Barrel valve leakage % should be  approx. 24% for most 360-400 engines with alcohol-  half as much for Gas  – about 15% for E-85  –  the more % the slower it will want to idle , but be colder when idling –  These injections do not like to idle under 1400-1500 and will  go crazy when attempting  to run them at a slow idle .
    Engines smaller than 360 will use less leakdown %-   305 on methanol will be closer to 16%  , same engine on gas  8% to 10%  or so .
    500 cu in engines will  need more fuel at idle , so use 25%-30% leakage for methanol-  half that much for gas .

    Secondary valve ( low speed valve,  also know as   idle check valve ) pressure  approx. 35#  with alcohol   25#   with  gas  

    Check throttle shaft wear by moving the shafts up and down when running to see if they are sucking air.   Approx .002”  is ok,,, more clearance will cause  idle to fluctuate.

    Imperative that you have more than one return spring –  need two , moderate tension springs pulling from the front and rear  OR from the center  with a second one near the front or rear of the injector  –

    When testing the barrel valve  leak % –  if it will not go down under 5%  , the barrel valve is worn out-   it should go to zero when turned all the way with the slot horizonal, and to 100% when wide open  .  Call us for a new Barrel valve  if it won’t leak down to close to zero when closed.


    Call Mike Chilando  at 615-457-3192  or e mail at  or  with questions