Lowandslow Posted September 26, 2013 Report Share Posted September 26, 2013 So I've had a problem with my idle the entire time I've owned my truck. Its a 1980 720 with the l20b and hithitachi carb. The problem I'm having right now is warm idle. I have hooked up the electric choke as it was not working before. It is now working and fully opening the choke. The thing is the idle is always at 1500 regardless of choke position. Also, when I start it for the first time it idles perfectly. After that, once its warm it will not idle at all unless I floor the gas pedal and get it to 3500 rpms for a second and once I do that I will have 1500 rpm idle again. I'm stumped by this and need some help!! Quote Link to comment
datzenmike Posted September 26, 2013 Report Share Posted September 26, 2013 Fast idle can be one or more of these things... Fast idle screw improperly adjusted. Throttle cable adjusted too tight Fast idle cam on from being badly adjusted or dirty/stuck linkages. Secondary throttle plate not fully closed. Worn primary throttle shaft or carb casting. Throttle plate rubs wall and sticks. BCDD vacuum threshold setting too low. Quote Link to comment
Lowandslow Posted September 26, 2013 Author Report Share Posted September 26, 2013 Oh man I was not expecting a huge list haha I will get to work on it!! Is there a special tool for the fast idle screw? I'm looking at diagrams and it seems to be set from undermeath Quote Link to comment
datzenmike Posted September 26, 2013 Report Share Posted September 26, 2013 The fast idle screw sits against the fast idle cam. As long as the cam is in the off position the fast idle screw isn't an issue. Here you can see the set screw (fast idle screw) one a step of the fast idle cam (ivory colored plastic thing) The cam should only be in place when the choke is ON. Normally it drops out of the way as the choke warms up and turns off. Hold throttle part open and just move it back and forth and spray with WD-40 to clean and lube the linkage. Quote Link to comment
wivrrat Posted October 7, 2013 Report Share Posted October 7, 2013 If that carb has a selenoid in it like my California 83 carb, you may be having the same problem I've been going thru. No power to the selenoid. You can adjust the idle screw all you want, but it won't help if the selenoid in the carb is not activating. You have to check the 6 plug wireing into the carb to see if the one firing the selenoid has power to it. The selenoid can be taking out of the nissan carb and it will idle smooth. Mine's running great with the selenoid out. Still working on finding out where I'm missing the power to the selenoid. Carb exchange in Fontana rebuilt mine and know all about the selenoid problem. They are great to work with. Cost me around $220.00 for the carb to be rebuilt by them. Good luck. Quote Link to comment
datzenmike Posted October 7, 2013 Report Share Posted October 7, 2013 The wiring from the carb to the connector is too short (to save a buck) and tend to flex and break inside. Yeah, check contenuity. Wiggle the connector and wires and see if the idle changes. Quote Link to comment
wivrrat Posted October 8, 2013 Report Share Posted October 8, 2013 From my experience checking this problem, it is not only in the 6 plug wire, but can be caused by the ECM or other component supplying power to the selenoid. The wire that supplies the selenoid has to be followed to the source. Quote Link to comment
datzenmike Posted October 9, 2013 Report Share Posted October 9, 2013 That would be the ECU under the driver's seat. But it reacts to input from throttle position switch on the carb that also goes through this plug. On top of everything there is a 'limp home' default mode if something screws up. The carb automatically goes to an over rich condition until fixed. Quote Link to comment
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