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When you experience “Spit back”  through the butterflies and sometimes spitting through the air vents in the nozzles –  Here are some things to check.

  • Barrel valve is set too lean
  • Butterflies may be bent
  • Bad Valve Job on the heads
  • Intake valve adjusted too tight
  • Vacuum  Leak around manifold or shafts
  • Timing too retarded – Generally timing should be 30-36 Degrees for unblown, injected engines except flatheads  – less for them
  • You may be trying to idle it too slow – 1200-1600 RPM is where it will want to idle

Butterfly gap for 8 Stacks:

The larger the engine, the more generous you can set the leakdown % since it will want more fuel at idle

.002” Methanol Leakdown % 16-25

.003” E-85 Leakdown % 12-16

.004” Gasoline Leakdown % 8-12