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Old 05-28-2013, 11:30 AM
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Carb Tuning QF750

Two separate questions:

1. In order to get the best idle, the 4 mixture screws are each turned out 3/8 turn. Is this an indication that something's wrong? I always hear that they should normally be somewhere between 3/4 and 1 1/2 turns out. What can I do to get them within the proper range and what would that do to drivability and mixtures at light loads?

2. When would I tune WOT a/f mixture with secondary main jet changes, and when would I tune with secondary main air bleed changes?

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Old 05-28-2013, 05:22 PM
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What engine is this on? what heads...cam?
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Old 05-28-2013, 05:27 PM
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What engine is this on? what heads...cam?
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Old 05-28-2013, 05:31 PM
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When you have it set to your "best" idle adjustment, if you create a vacuum leak, does the Idle speed increase and improve?
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Old 05-28-2013, 05:36 PM
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Carb Class: Baseline Setting for your new car
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Old 05-28-2013, 05:44 PM
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When you have it set to your "best" idle adjustment, if you create a vacuum leak, does the Idle speed increase and improve?
No. It will stall.
No vacuum leak, carb brand new. All surfaces flat and sealed. Floats set @ 1/2 sight glass at hot idle. Idle speed 1100 RPM, 10 in-hg, best and most stable idle.Initial timing 20 plus 17 cent all in @ 2500. 12 degrees vac advance @ about 5 in-hg.
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Old 05-28-2013, 05:52 PM
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Put in larger Idle feed restrictions , it sounds lean at idle.
Be sure the throttle plates arent starting to cross the transfer slots , that will indicate the need for larger Idle feed restrictions.
10 inches of mercury ,isnt that pretty normal for a cam that large?
Whick Quickfuel do you have ? the SS?
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Old 05-29-2013, 04:49 AM
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Put in larger Idle feed restrictions , it sounds lean at idle.
Be sure the throttle plates arent starting to cross the transfer slots , that will indicate the need for larger Idle feed restrictions.
10 inches of mercury ,isnt that pretty normal for a cam that large?
Whick Quickfuel do you have ? the SS?
Q- Series Carburetor 750 CFM DRAG

Transfer slots are AOK, about .020" exposed. I can idle it at 900 @ 8 in-hg if I want to, but rather have it fast at 1100 (cam oiling and throttle response both better).

Idle a/f ratio measured @ 14.5 with wideband.
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Old 05-29-2013, 05:04 AM
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[QUOTE

Idle a/f ratio measured @ 14.5 with wideband.[/QUOTE]

This is the problem IMO.
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