How To Adjust The Choke and Fast Idle on Holley Carburetors
Today I'm going to give you some tips and tricks on setting the choke adjustments as well as the fast idle on a Holley carburetor.
If you need to set the choke, maybe because you don't have the original settings or someone had it pinned open or had it out of adjustment. One of the ways to get a good starting point is simply to loosen up the choke housing screws on the retainer. Loosen them up just enough to allow you to rotate the choke cap but not enough to allow it to freewheel. Slightly crack the throttle open, unload the fast idle cam, and turn the choke cap clockwise until you see the choke plate open. Then rotate it back slowly until the choke plate just comes closed. At that point, you can go ahead and snug those screws back up, and that's going to give you a good starting point to make adjustments from.
If you look at the top of the choke housing you'll see some witness marks or register marks that you can use to reference if you are making adjustments with more or less tension. Depending on the engine combination or the climate, the vehicle's going to need that choke to stay on a little bit longer or come off a little bit quicker and you are going to make those changes by just increasing or decreasing the tension by rotating this cap on the bottom metal choke spring.
Now that you've got your basic choke settings correct, we're going to talk about the fast idle. This can be frustrating sometimes because you generally have one shot in the morning when the engine is cold to get this adjustment right so you may find it takes several days to get it adjusted. The reason for that is, if you start the engine and it's not right you need to shut the engine off while you are making adjustments. It changes the engine's heat soaking and it's changing the overall dynamic of the engine. The little trick I'm going to give you is going to allow you to generally get it set pretty close to where it needs to be in one attempt. Here's my method of doing it. With the engine completely cold, I'll open up the throttle and I'll back my fast idle speed screw off to where the throttle is shut, choke is closed, and it's not catching the cam. At that point, I'll get a buddy of mine to start the car and when he starts it I'm going to take a screwdriver on my curb idle speed screw and I'm just going to crank that up real quick to get to my desired fast idle speed. If I'm satisfied with the operation then I'm going to let it warm up, the choke comes all the way open, and if I'm happy with it. At that point I can shut the car off, manually close the choke, and look at the relationship of my fast idle screw to the cam, I can roll my throttle open and make adjustments to the fast idle screw until it comes up and it contacts the fast idle cam. Now that we have our fast idle adjustments set correctly we can go ahead, start the engine up, get it back up to operating temperature, make sure that the choke is open, and back the curb idle speed screw down to our desired curb idle speed. This method is going to generally allow you to get it dialed in to where you need it to be in one setting and possibly you just have to make a couple of little small adjustments accordingly. For more helpful Holley tech tips and videos, go to Holley.com
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