Thread: Fast Idle
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Old 05-03-2016, 04:55 PM
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DanEC DanEC is offline
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Join Date: Apr 2009
Location: Little Rock area, AR
Cobra Make, Engine: ERA Street Roadster #782 with 459 cu in FE KC engine, toploader, 3.31
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Hi Phil - not sure what phase you are in. The first thing to do is set the idle mixture screws which are the screws on the side of the fuel bowl in the side of the metering plate. Since the carbs are mounted backwards, the metering plates are on the rear side of the carbs. A starting point is to usually lightly bottom all four of them (both carbs) and then turn each one out 1-1/2 turns.

Then back out the idle speed screws which are on the passenger side down just above the carb base plate. Back them out until you can see that they are just losing contact with the cam they bear on. Then screw them back in say 1 full turn - not sure where you will be with there but hopefully it will idle.

Depending on how you intend to adjust your idle mixture, hook up a vacuum gage or a dwell/tach unit if adjusting it based on rpm. Either one will work but I kind of like a tach.

Start the engine and if it's idling too high or low, adjust both idle speed screws equally until it's idling at an appropriate speed to proceed with. On the front carb turn one side's mixture screw in and out while watching the tach and adjust it for the highest rpm. Then go to the other side of the same carb and do the same. Then go back to the first mixture screw and play with it a little to make sure it's still set for the highest rpm. Basically you are just tweaking the mixture screws to achieve the highest rpm which is the most efficient setting.

Once done with the front carb, go to the back carb and repeat this, adjusting for the highest rpm. If the idle speed creeps up too high (say over 1000 rpm), turn both idle speed screws back an equal amount (CCW) slightly to lower it back down. Back down both screws the same amount so that both carbs are equally contributing to idle. Once you have the rear carb mixture screws adjusted for the highest rpm you can call it good or go back to the front carb and fine tune it a little further. It's sort of a back and forth process to optimize the mixture settings.

Once that is done it's just a matter of adjusting both idle speed screws equally to the idle speed you want. But always make equal adjustments to the idle speed screws on the two carbs.

This is basically the way ERAChas recommended setting up dual quads.

Good luck. Let us know how it goes.
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