Post by
Davezilla »
https://forums.nicoclub.com/davezilla-u195464.html
Sun Jan 15, 2012 10:33 pm
First of all... Welcome to the forum!!
Now for your carb... The screw you got marked in green down by the base is the idle speed adjustment and it should let you adjust it down to or below the 850 rpm idle speed but the fast idle cam needs to rotate off it's steps so the idle will go down as the engine warms up. The other screw looks like it's for the accelerator pump.
The basic way the electric choke works is by choking the engine for cold starts and raising the idle speed. the idle speed won't come down automatically but by the opening and closing of the throttle as in normal driving, same for starting on a cold morning, you press the gas once, which not only squirts a little fuel into the manifold but also resets the choke to the full choke position, as the heater in the choke heats up the bi metallic coil it slowly opens up the choke as you drive. The fast idle cam operates as you drive when the choke is open enough the cam is allowed to roll over to a lower setting, again done by normal driving or actuating the throttle as the engine warms up, it can't move off the fast idle setting without some throttle input.
Now with the basics of how it all works out of the way, here's what to look for... Is the electric choke fully closed before the engine is started? ( you may need to cycle the throttle one time and the choke should snap shut) And does the choke open up all the way once the engine warms up? If the choke don't open all the way, you may need to loosen the 3 screws on the side of the housing and rotate it until it's fully open after the engine is warmed up, the carb can't come out of fast idle mode until the choke is fully open. So the first thing you'll need to do is check that the choke both fully closes when cold and fully opens after it's warmed up and make the appropriate adjustments.
With the choke adjusted properly you can cycle the throttle and check that the fast idle cam is rotating out of the way and getting the carb out of fast idle mode, you can also hold the choke open and give the engine a rev to see if it returns to slow idle, but it needs to be free enough to do this on it's own.
There's also a small vacuum actuator connected to the choke mechanism called a choke pull off that does exactly what it's called, it's meant to pull the choke off at full throttle. This choke pull off can also interfere with proper operation if it's not working, check it by removing the vacuum line and connecting it to a vacuum pump, it should pull inward and stay that way as long as vacuum is applied. To test it without a vacuum pump, you can push the rod in while blocking off the vacuum inlet with your thumb, the rod should not come back out until you move your thumb off the inlet.
Once all these components are working properly your idle speed should go down as you adjust the screw out as long as there's no vacuum leaks.
Hopefully that covers all the choke mechanism's inner workings to give you a few things to check for in that area... only other thing I can think of that would cause the idle to be too fast is vacuum leaks, but a faulty vacuum advance or power brake booster can also hide a small leak just big enough to make your idle fast or erratic.
