On top of my brand new 300 I have a new 390 4bbl holley. My question is how do you set the idle speed? I know you use the primary idle speed screw but mine does not touch against the screw unless I push down on the opposite side where the choke is. There is a red plastick arm that attaches to the choke and when I push that down the idle speed comes down and it contacts the primary idle speed screw. As soon as I rev the engine a little the idle won't return, it stays around 1200 rpms. I have check with the throttle cable disconnected and nothing else is hitting. I also checked the fast idle screw and that is right on the money according the the instructions I got with my holley. Can any give me some help? Thanks

 

It sounds like the choke is not opening fully for whatever reason. Either the truck is not fully warmed up or a choke problem? Let us know what type of choke it has and perhaps I can offer more assistance.

Lou

 

It has an electric choke on it. I guess I will have to check and make sure I am getting the 12 volts to it. The carb is brand new, but I did take the choke off to swap the vacuum secondaries to the quick change kit. Everything went back together just fine. I read somewhere that you can adjust the choke by loosening the three screws and try turning it. Is that correct? Thanks

 

The red plastic arm you describe sounds like the fast idle cam for the choke. In order to hold the idle speed up, the choke is probably still slightly engaged. Is the choke "butterfly" fully open when the truck is warm? If not, check for 12 volts at the choke. Also check for a good ground. Ground your test light to the carburetor housing to make sure. Yes, it is possible to adjust the choke using the 3 screws around the housing but don't touch that until you are absolutely certain nothing else is wrong. Usually, that adjustment is pretty close to perfect from the factory and it's not one you'll want to change drastically. If you do change it, move one increment at a time until you reach an acceptable adjustment and keep notes in case you need to go back to where you started.

Lou

 

Thanks for the help, I checked the power to the choke and I had a broken wire. I got the 12 volts to it now. It idles great at about 800 rpms. I have just a bit of tuning to do now on the carb. I have a bit of hesitation when I stomp on it in any gear. Im sure that is the accelerator pump cam or shooter I'll have to play around with. Thanks for the help once again. This is my first 4bbl carb.

 

Make sure the ignition is in good working order before adjusting the carburetor. The idle mixture may be a little too rich, it could need some tweaking on the accelerator pump, or the secondaries may be opening too quickly. Holley makes different springs to adjust the secondary opening speed. Good luck with it.

Lou