Quick and easy question for you guys

Hey guys, got an easy one for ya. I've got a 450 EXC, and I recently raised the idle to about 1800RPM since it was really low and made the engine pretty noisy. Once I got the fuel mixture dialed at operating temp, it raised it even more, to the point where it's hovering between 1900-2000RPM. I think that's a bit too high, so I'm gonna bring it back down to 1800-ish when the rain lets up (unless you guys think that is an OK idle speed? it sounds and runs fine, but the number just seems high to me). My question is, if I'm making a small idle adjustment like this, is it really necessary to adjust the fuel mixture again? Will this small change in idle have any effect on the fuel mixture? Obviously it isn't a huge deal to pop the little fuel screw adjuster back on and run it back and forth a couple of times to verify that it's still tuned correctly, but I was just curious if it will have an effect. I would go out and try it right now, but the rain has moved in and it's supposed to be storming all week. I have no garage to work in, unfortunately.


That's not how you tune the pilot circuit.

Hot motor, drop the idle as low as it will go, and put the fuel screw at 1 turn out.

Now turn out the FUEL SCREW to raise the idle.

Repeat as needed.

The idle should be adjusted USING THE FUEL SCREW as the last thing you touch.

If you do it with the idle/slide already up, you will be compensating a lean condition (high slide) and have hanging idle and a flat spot.

Hmmm. Well, the fuel screw IS the last thing I touch, following the procedure in the manual. Maybe it's a bike or carb-specific thing, but the procedure in the manual and what lots of others say to do is: start with the fuel screw 1.5 turns out, use the idle adjustor screw to set a ballpark idle with engine at operating temp, turn fuel screw in until idle decreases, turn it out until it increases then decreases again, find the spot in between those two points and leave fuel screw there. If that fuel screw adjustment has ended up with higher than your desired idle, repeat that same process, adjusting the idle and then adjusting the fuel screw again each time. If fuel screw is higher than 2.5 turns out or lower than 0.5 turns at ideal setting, change pilot jet, yada yada.

My question was basically whether I can take a shortcut and just bump the idle adjustor screw up a small amount without needing to re adjust the fuel screw too. Essentially, assuming I am close to my target idle and have a correct fuel screw setting, will turning the idle adjustor a tiny amount affect the mixture significantly?

For what it's worth, I believe I am adjusting the fuel screw correctly. The bike starts first kick every time, idles smoothly, feels strong, no hanging, no flat spots, no surging, no smoke, no backfiring, no overheating, no spooge etc. etc. . I have no problems with how the bike runs, I'm just asking a general question about this idle procedure (also it's more of an "I wonder" question since adjusting the fuel screw is an easy step anyway, so it doesn't truly matter one way or the other). Maybe I should have posted this to the make specific forum? I thought it would be more of a general principle though. 

Edited by hershmagersh

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