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Old 12-11-2008, 02:48 PM
oldbogie oldbogie is offline
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Where I was headed, is that engines pulling a lot of cam often cause the tuner to tip in too much throttle opening to get a decent idle. Your cam and lifter combination certainly qualify as one of those where if you're not careful you could tip the throttle plates open enough to where the transition slots are exposed to the manifold side of the throttle plates. In that case the transition slots will start feeding fuel making for a rich idle mixture that can't be controlled with the idle screws.

If this is the case, then looking down the primary throttle bore the plate will overlay the transition slot from some to all of it. The solution is to give the engine another source of idle air such that satisfactory idle can be achieved with the throttle blades closed to where all of the transition slot is above them.

Some Holley's have 4 corner idle circuits with a simple adjustment for throttle blade position on the secondaries. Other Holley's have a screw stop adjustment on the secondary accessible from underneath the carb. This can be used to crack the secondaries enough to get more idle air into the engine, allowing the primary plates to be repositioned properly. The last option is to drill a couple small .060 inch holes in each primary blade as an additional source of idle air, which again lets you adjust the primary throttle plates to a position under the transfer slots.

If this is the problem, then these type changes should put you back in control of the idle mixture.

You need to keep in mind that 1.6 rockers make the cam look bigger to the engine. While not adding duration, they increase the rate of change in lift relative to duration. The engine will react to that as if there was more overlap, the LSA was tighter, and closing intake valve as well as the exhaust was later, while opening events seem earlier. So you're alreading using a pretty aggressive cam, that with the 1.6 rockers will easily get you into idle adjustment problems.

Bogie
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