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Old 09-18-2008, 04:21 PM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by kbyounger
I finally got my three deuces on, connected and running!!!! But, when I rev the engine to the point that the secondaries open, the center carb will Pop or backfire as they first open. If I rev it slowly to the point of where the secondaries will begin to open, then the engine "bogs down - or hesitates. I have heard that the floats in the fuel bowls must be set exactly right or the secondary carbs can be too lean or rich... Is this what would cause the center to backfire? Any ideas are greatly appreciated. I'm so close to getting these things running... thanks - kip
Mechanical linkage I presume. This is a common problem. When the secondaries open the total flow area is increased and the instant flow in the primary carb is reduced. This messes up the mixture, the engine will backfire and stumble till it starts to gain some revs to get the air flow in all the carbs up to where main metering is working.

It's a tuning issue. Certainly as you were told; the floats have to be perhaps a bit high, making it easier to draw fuel with less air flow in the venturi. The accelerator pump needs to be played with as well to help hide the lean drop. Secondary throttle timing needs to be adjusted to open the throttles slower and perhaps later in the opening cycle.

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