Setting Idle Gap

Added: 2026-05-14

[00:00:05]How's it going? Adam Drake here and today I'm going to share some information on setting idle gap.

[00:00:10]So, idle gap is super important.

[00:00:13]Um, it's something that is sometimes overlooked and is a little bit tricky to measure or get the adjustment on. So, like with the low speed needle, it's pretty easy to set and get the measurement for what the low speed adjustment is, same with the high speed as well as the mid speed. All those needles are exposed. So, it's pretty easy to get to and set. On our website, drakeracing.com, we have carburetor settings for pretty much any of the OS based engines.

[00:00:50]Um, but as far as idle gap goes, it's a little more tricky. Um, you have to have the filter removed. You also need to remove the venturi.

[00:01:03]And the idle gap is basically the gap that the slide is open that allows the engine to idle.

[00:01:13]So, the standard setting for pretty much any OS based engine, whether it's a 21J or 22E carburetor, you will want to start with that idle gap at a half a millimeter.

[00:01:28]Now, you can kind of eyeball it if you have a good eye and you know what a half millimeter looks like, but we're going to make it a little bit uh simpler and also kind of a safer way to ensure uh you're at that half millimeter setting. So, I've seen some guys take, um I believe it's like a spark plug gauge, like a almost like a little gap gauge or feeler gauge.

[00:01:55]Um, I like to just use a zip tie because it's it's not metal, it's not going to damage anything.

[00:02:04]Um, and what you'll want to do, because obviously there can be a variance in zip ties, just make sure that the tip of the zip tie you're using goes to a half millimeter. If the zip tie is a little bit bigger, you're not going to be able to set it at a half millimeter. If it's too small, idle gap's going to be a little too low.

[00:02:24]So, what I do is I will just take, with the slide just slightly open, as you can see the boot kind of pushes slide open a little bit, I will drop the zip tie down in there.

[00:02:39]And as you can see, the zip tie is getting stuck. It's not coming out, so that gap is slightly under a half a millimeter because it's actually pinching the zip tie.

[00:02:53]So, if I just hold the engine upside down, and I turn in the idle screw until the zip tie, like you can see there, it starts to move and then it drops out, that tells me this is now at a half mil or maybe just slightly over because again, it allowed this to fall out.

[00:03:14]So, that half mil adjustment is a very, very good reference or starting point. Uh, any of the engines that we break in come preset from the Drake Racing um with the low speed, mid speed, high speed and also idle gap already set.

[00:03:34]Um, I've heard some people say you set the idle gap to a half mil and you never change it, never adjust it.

[00:03:42]You should just tune the bottom and mid and that idle gap should always stay at a half millimeter and that is absolutely false.

[00:03:51]Um, again, that half millimeter is kind of the standard or the baseline, but there are so many variables.

[00:04:00]The idle gap may change depending on the venturi you're using, the fuel, um the tune or feeling that you like on track.

[00:04:10]I would say if anything, that half mil idle gap is on the safe side or a slightly higher idle if the bottom and mid speed are adjusted properly.

[00:04:22]So again, I always like to start at that half mil setting, but then I tune the engine to get the power and run time that I desire.

[00:04:33]And normally, I will then have to reduce that idle gap below a half a millimeter.

[00:04:39]The half mil again is just a good baseline.

[00:04:44]Um, if the engine starts to get tired, lose compression, lose seal, um you may need to bump up that idle gap slightly for it to to have safety and idle, especially when landing jumps.

[00:04:57]Um, but again, just wanted to kind of show you how simple and easy it is. I don't go So, basically, I'll set my idle gap at a half mil and I don't go back and check it later.

[00:05:12]Um, I don't like pulling the air filter off all the time, especially you know, after you run on a dirt track, you don't want any of that dust or dirt to fall down into the carburetor.

[00:05:23]If you get lost and you're just you're kind of want to make sure you get back to home, it's fine to pull air filter off to reset the idle gap to a half mil, but that idle gap is mainly uh important when the engine's new, which again, we set it at a half a mil.

[00:05:40]And um, but again, if you get lost, this is just kind of a simple way to set your idle gap, but also know it does not have to stay or be at that half mil setting. You can in most cases run below half mil. That uh that less than half mil idle gap will um help with run time. It will help the engine come down to idle um a little bit quicker and easier.

[00:06:12]Um, but again, if the engine's a little bit tired, you may have to run slightly higher than that half mil setting, but um again, just wanted to show how to set your idle gap on an OS speed engine.