Thought I'd share this because I see a lot of people wondering how to adjust their idle mixture. On some bikes it's really hard to get at the idle mixture screw and near impossible once the engine's hot. I'm a mechanic and need to adjust mixtures accurately and so I made this tool to do it. It's a piece of wood about 12mm square, with a screwdriver made out of a small bolt, and the drive belt, gear and tensioner out of an old printer. It cost nothing and only took about a half hour to make once I'd decided how to do it. Anyone that works on a suzuki quad needs one. The standard setting as recommended in the manual is only a starting point, and they always run nicer with a proper adjustment. The gear at the screwdriver end is pressed on there and is tight enough to turn mixture screws if they are not seized. The adjustment should be done warm, and it's supposed to be the highest revs you can get with the least throttle opening, then you wind the mixture screw in until the revs just start to drop. That settings called "best lean", and it's what they run best at when hot. Sometimes though if the bikes doing a lot of stop starting I leave them a fraction richer than that.

I bought one of these Ratchet Wrench, Mini 36 Teeth 1/4in Drill Bit Socket Ratchet Wrench Screwdriver Sleeve Spanner Car Hand Tools(Orange), Socket Wrenches - Amazon Canada and I still had to grind half the hex shaft off a slotted bit before it would fit under the carb on my quadrunner. And then turned out there wasn't enough room sideways to swing the ratchet! So I have to stick my fingers in there and spin the teeth....

If we take a carb that is tuned properly to run from just off idle to WOT then there will never be a shortage of fuel at any opening above idle. Then if we tune the pilot circuit such that the carb idles with the slide open a bit then there will still never be a point where there is a shortage of fuel. The only issue with tuning it like that is: because the slide is open a hair the engine needs to develop more vacuum to draw gas out of the needle jet which makes it harder to start manually, but it's not an issue with electric start. The advantage is the tuning procedure is easier because the pilot circuit is less relevant and the throttle response is crisp with no stumbles. Your way requires everything in the carb be absolutely perfect (slide cutout, pilot jet, air jet) in order to have seamless transition from idle to off-idle, and that's often not the case, especially with aftermarket carbs or switching carbs to different engines or tuning stock carbs after modifying engines. There are a range of slide cutouts available and you can't just pick one and make it work. There are a range of jet needles and needle jets and pilot jets and air jets. It's a puzzle with at least 5 variables to tune to make work right just to transition from idle to off-idle. So to avoid that nightmare I just tune it with the slide open a bit then there is no transition to worry about. The downside is it's hard to use a pull cord or kick starter to generate the vacuum necessary to draw fuel out of the needle jet with the slide open a hair. If not for the issue of starting, a pilot circuit wouldn't be necessary at all.

Yeah well the reason you have that problem Randy is because the way you do it, you are using both the idle discharge holes as one. There are two discharge holes into the venturi right by the butterfly, one on the engine side and one on the aircleaner side of the butterfly, when it's closed properly. When the butterfly is closed off the idle mixture is supposed to come up from the adjustment needle and get sucked out the hole nearest the engine, but, the mixture is getting diluted by an extra measure of air getting drawn in through the second hole, the one away from the engine. Because of that extra air, we end up adjusting the idle mixture slightly richer to get it right. As the butterfly starts to open, the second hole starts to have vacuum applied to it and it starts discharging fuel as well, and, at the same time, the first hole doesn't get extra air anymore.That second hole discharging combined with the now undiluted mixture out the first hole is what stops the flat spot you have when you adjust it your way. The way you do it Randy, you have both holes discharging fuel at idle, and because of that, you have the idle mixture screw wound in more than it should be. It gives the right mixture at idle, but when the butterfly opens there is a shortage of fuel.. it's being restricted by the idle screw. If we want our bikes to run right, it's important to set the idle mixture with the least possible amount of throttle opening. Once the idle mixture is right, at a slow idle, we can wind the speed up a little if we want.. but don't start adjusting the mixture again or you will start going around in a vicious circle of mixture/speed/mixture/speed, which will lead to the symptom Randy describes.. a flat spot.

You just poke the screwdriver end in from the right side of the bike on a suzuki, (after taking off a small bit of black plastic if it has one in the way), then raise/lever the screw driver up into the idle mixture screw's recess, turn the pulley on the outer end till the screwdriver engages, and then turn the outer gear to adjust the mixture. I'm always careful to keep the belt from touching the hot motor,(it's pretty close), but it has touched a few times and seems reasonable heat resistant. That's the third design of tool I've made and far and away the simplest and best to use. From one pulley to the other is about two-hundred mills, the screwdriver length is a bit critical because if it's too long the pulley won't fit above a cast bit of the bowl, and if it's too short it won't engage with the screw. I left the screwdriver a bit long until it had the gear pressed on, then held the bolt head in the vise while I cut it to the right length and filed it to a screwdriver end. I think from memory there's about five mills of leeway on the length of screwdriver, perhaps a little less, three mills perhaps. The printer I pulled apart had several gears I could have used, but I could see that a small diameter would give more room.. As it happened a gear any bigger than the one I used would have touched the carby and caused the screwdriver to be at an angle. I can measure the diameter if you want. That belt by the way is like a cam belt, it's got teeth on it so it's a solid drive.