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Glenfield Glenfield is offline
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Join Date: Apr 2020
Location: Chicago, IL
Posts: 522
I'm having to come up the curve quicker than I'd like on carbs but I think of the idle and progression circuit as functionally the same circuit. Idle/progression blends into main ... where and how it blends, depends on:
- position of throttle valve vis-a-vis progression holes ... too exposed at idle and it brings in main circuit sooner (not your condition)
- size of idle air corrector (or maybe even idle jet) ... this could be it but I'd h have expected it deeper into RPMs. If it's too small, it may lean our idle/progression circuit at higher RPMs within the idle/progression circuit
- idle mixture screw ... if too far in to get idle AFRs acceptable, it leans out the air/fuel mix flowing through the progression holes which will bite right before mains takeover
- emulsion tube ... when it brings in mains as you described above.

I could have that all wrong but it is my best attempt at unpacking the theory.
Old 08-12-2025, 08:11 PM
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