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Old 12-12-2010, 09:18 AM
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inconsistent idle/ motor surge

i have a 1977 ford f100, 302 with an edelbrock performer intake and performer carb. Once motor has reached normal temperature, the rpms will not stay consistent and the motor begins surging from 1400rpm done to 700 or so. I've fixed a few vacuum leaks and pulled the carb, checked floats, jets, ect.. and things look ok. a little corrosion on the metering rods. one main concern is the right air/fuel mixture screw, is not working. Would this be causing the surging problem and or could something else be causing the problem?

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Old 12-12-2010, 10:45 AM
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Usually when a idle mixture screw doesn`t work it means there`s excessive trash in the idle circuit so no fuel is flowing through it. That or the fuel pressure is too high forcing fuel out of the booster or the float level is too high or the timing is too low which means the butterflies are open too far resulting in it pulling fuel from the boosters instead of the idle circuit. But since it`s only one side I`m thinking the idle circuit is plugged. Why the idle goes up and down is because it`s not getting any fuel on that side so it`s forced to pull it from the main booster which is giving it far more fuel than the idle circuit ever would so the idle goes up from the excessive fuel. Yank the carb and rebuild it, clean out all the passages so you know they are working correctly. If you were using a open plane intake it wouldn`t be as obvious, as 1 runner pulls off the entire plenum of the carb. On the dual plane performer it`s divided so you have one side getting fuel and the other getting nothing.
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Old 12-12-2010, 12:54 PM
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