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Fast Idle Solenoid/Curb Idle adjustment


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2 replies to this topic

#1 usn27sun

usn27sun
  • Inactive
  • 154 posts

Posted August 20, 2007 at 12:51 pm

Greetings All, I have a Carter T-Quad on my 340 and I am not sure as to how to adjust the idle screw that contacts with the solenoid switch. Every diagram I have seen of a Thermoquad has the solenoid switch mounted on the passenger side of the carb, mine is installed on the drivers side. The car is an automatic. Can anyone tell me just what this solenoid switch does and how to adjust it. Thank you for your time.
usn27sun

#2 Volunteer

Volunteer
  • Active Member
  • 2,418 posts

Posted August 21, 2007 at 02:19 am

Hello, Bill, nice to see you are still with us. This is a '72 carb? You know it's the solenoid because of the electrical connector, otherwise it'd be a dashpot. It's quite simple really.
The threaded stem is meant to be turned in or out as it contacts the throttle shaft. Since I don't have one (installed) to readily refer to, experience shows that the solenoid (housing) itself may thread in and out of the mounting bracket. Regardless, turning clockwise will increase speed. This device should maintain a 'fast' curb-idle of approx. 900 rpm's while the regular/manual adjusting screw allows the throttle plates to close farther to a much slower 5-600 rpm's. The theory behind this is that the engine will be less likely to exhibit 'run-on' once the ignition is turned off because the throttle plates will be closed sufficiently to prevent excess fresh air to enter the intake system.
It's best to set the idle speed after the engine is fully warmed and the timing and mixture are optimal. Adjust the solenoid to maintain the 'fast' curb idle. The other adjusting screw should be 'floating', approx. one turn from contacting throttle stop.
Disconnect the power to the solenoid and note whatever decrease in idle speed. Set this 'slow' curb idle to about 500 or whatever it wants to keep engine running. Do not have it too slow because if the solenoid ever failed and some accessories were also operating you'd instantly lose 'driveability' ( or possibly stall) until you could get under the hood to crank it up a bit.

Edited by Volunteer, August 21, 2007 at 02:29 am.


#3 usn27sun

usn27sun
  • Inactive
  • 154 posts

Posted August 29, 2007 at 07:47 pm

Hello, Bill, nice to see you are still with us. This is a '72 carb? You know it's the solenoid because of the electrical connector, otherwise it'd be a dashpot. It's quite simple really.
The threaded stem is meant to be turned in or out as it contacts the throttle shaft. Since I don't have one (installed) to readily refer to, experience shows that the solenoid (housing) itself may thread in and out of the mounting bracket. Regardless, turning clockwise will increase speed. This device should maintain a 'fast' curb-idle of approx. 900 rpm's while the regular/manual adjusting screw allows the throttle plates to close farther to a much slower 5-600 rpm's. The theory behind this is that the engine will be less likely to exhibit 'run-on' once the ignition is turned off because the throttle plates will be closed sufficiently to prevent excess fresh air to enter the intake system.
It's best to set the idle speed after the engine is fully warmed and the timing and mixture are optimal. Adjust the solenoid to maintain the 'fast' curb idle. The other adjusting screw should be 'floating', approx. one turn from contacting throttle stop.
Disconnect the power to the solenoid and note whatever decrease in idle speed. Set this 'slow' curb idle to about 500 or whatever it wants to keep engine running. Do not have it too slow because if the solenoid ever failed and some accessories were also operating you'd instantly lose 'driveability' ( or possibly stall) until you could get under the hood to crank it up a bit.


Thanks Volunteer, for years I have been adjusting the idle with the slow idle screw just above the solenoid switch. I never had a problem with run-on, however, setting the idle speed employing the solenoid has made a very nice difference in ideling and driveability. Why? Does this adjustment effect more then run-on? I hope all is well with you and the great north-west. Will talk to you again soon. Thank-youall.


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