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Two-Stroke Scooter / ATV Carburetor Settings And Adjustments 2of4 : Idle Speed & Mixture

Part 2 of a 4 part video detailing all of the basic settings and adjustments of the carburetors found on Minarelli / Jog / 1E40QMB powered 50-90cc scooters and youth ATVs. Part 2 shows how to adjust the idle speed and mixture settings. Please like the video if you found it to be helpful.

The first adjustment i’ll show you is a really simple one let your idle speed the screw right here if you screw this inward clockwise it will raise your idle speed and if you screw it outward counterclockwise it should lower your idle speed if you look through the carburetor you can see what the idle speed screw actually does if you screw it in here you can see that

Throttle valve a slide opening up raising up inside the carburetor and that’ll let more air and fuel pass by at idle and of course if you screw it outward it lowers down and lets less fuel and air pass by at idle so the higher the more that’s open the higher idle speed is and the more it’s closed the lower your idle speed is now move on to the idle mixture screw

And what that does is it helps control the mixture along with a pilot jet from idle up to about an eighth to a quarter throttle you’ve got an opening here on the front of the carburetor that lets air through into a passageway and this idle mixture screw here is actually in that passageway so when you screw that in it blocks off the airway obviously allows less air

In the richen up the mixture when you screw it out it opens up allows more air in and leans out the mixture before making any adjustments to the idle mixture screw i’d suggest screwing it in and counting how many turns and it goes so for example this one there’s a half a turn one turn one and a half and two turns gets it snug don’t force anything so that’s two

Turns out word is where i was set and you want to make note of that write that down or something so you know where to go back to if you have trouble to start off with i would suggest one and a half to two turns out so i’m just gonna go ahead two turns out on this half one one and a half and two turns out when you adjust the idle mixture screw you’ll want to have

The engine warm so make sure you start the scooter and let it run for five minutes or maybe even take it down the road to get the engine good’n warm because you don’t want the automatic enricher affecting your adjustments here and that’s gonna work until the engine’s warmed up a little bit to adjust the idle mixture screw you’ll start out by turning it one way or

The other it doesn’t really matter about a quarter of a turn then you’ll let it settle for a second and see if the engine idle increases decreases or stays the same if it increases then keep going the way you were going a quarter turn at the time again let it settle listen again if it stays the same keep going the same way you were going and if it decreases go back

The opposite way a quarter turn at a time but each time you’re going about a quarter turn give the engine a few seconds to settle listen for increased or decreased idle speed and you’re doing this to accomplish the highest idle speed that you can get out of this idle mixture screw if you end up with this screwed all the way in for the best idle the highest idle

That’s blocking off all the air for the richest setting so that’s telling you that your pilot jet is actually too small so you should really move up on the pilot jet size and then readjust this if you get the best idle with a screw screwed way out like you see here that’s allowing the most air through so that’s telling you your pilot jet is actually too large and

You’ll want to try going down a step on pilot jet size if this is wiggling around that’s not safe because with all the vibration of the engine and stuff you may end up losing this screw there’s a little spring behind it that keeps tension on it and if it screwed out too far that springs not going to keep enough tension to keep that secure so again if it screwed

All the way in for the best idle then your pilot jet is too small if it screwed all the way out or very far out then your pilot jet is too large you

Transcribed from video
Two-Stroke Scooter / ATV Carburetor Settings And Adjustments 2of4 : Idle Speed & Mixture By 49ccScoot