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Old 09-18-2008, 12:44 PM
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tri carb help

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

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Old 09-18-2008, 02:28 PM
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It's a legitimate tripower setup, no accelerator pumps on the outboard carbs? Cam you being those carbs in sooner and see how that works? You may have a ton of timing coming in early, what's the timing when they start to open? Unless you're accelerating hard, if you have fuel in the bowls free revving it, you're not going to starve it for that split second while transitioning.
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Old 09-18-2008, 02:37 PM
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OK, no its not a real tri power set up, the outside carbs have been altered to make it "tri power." The only thing I know about timing is that the engine is set at 7% advanced, but I don't have the knowledge or tools to watch the timing during acceleration... someone mentioned that perhaps bringing the carbs in later, would help, because it sounds like it is running lean... I can certainly play around with where the carbs come in at, and if that does not take care of it, then I suppose I could then check the float levels... any other thoughts? thanks - kip
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Old 09-18-2008, 03:47 PM
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It does sound like a lean condition, so try bringing the end carbs in sooner, not later.
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Old 09-18-2008, 04:21 PM
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Quote:
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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