Backfire Through Intake Of Front And Rear Carb At 3.5 Turns Clockwise

[jalexquijano]

Installed long needle valve and seat in front bowl and short in rear carb bowl, set the gap to .55 inches and tuned it to 2.5 turns clockwise. Engine stumble and falls. Increased to 3.5 turns clockwise and it backfires through intake. Could one of the neddle and seat fastened at the bowls be damaged?? This is not normal. My electric pump is brand new and is measuring 3 psi.

[Cozza]

Sounds lean. Try screwing the seat at the base of the carb needle down a little more.