Idle mixture screw inquiry... lean vs rich adjustments - Yamaha Grizzly Forum : GrizzlyOwners.Com Yamaha Grizzly Forums


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Old 02-22-2007, 08:01 AM   #1 (permalink)
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Default Idle mixture screw inquiry... lean vs rich adjustments

Hi Guys!
A question here; if someone is monkeying around with their carb settings, and they find the idle mixture screw on the bottom side of the carb, does turning it in richen or lean out the mixture?
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Old 02-22-2007, 05:38 PM   #2 (permalink)
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Bob, I don't think it does either if we're talking about the same screw. Do you mean the one with the black knob to increase idle speed? If that is the case, by screwing it in you are just advancing your throttle and making it run at a higher RPM when you're ideling. I believe the only way to make it rich or lean is by changing jets and needle position but I'm not an expert on carbs by any means.
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Old 02-22-2007, 09:29 PM   #3 (permalink)
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Hi Starky!
That one's just the idle adjustment on the side of the carb. The screw that I'm wondering about is on the bottom of the carb on the inlet tract side. The Shop manual just says to put it back where you found it and makes no mention of which direction actually richens or leans the mixture. I'm curious about this because my Grizzly when stock was almost as cold-blooded as a mid-eighties Honda. A couple of my riding buddies have Grizzlies, so I thought that some advice for them might make for an interesting afternoon of fiddling with adjustment scres...
Hey! Are those tracks getting a workout?
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Old 02-24-2007, 01:48 PM   #4 (permalink)
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I took the tracks out on Wednesday and tried to climb a snow drift and got stuck. Of course I didn't have a shovel so it took me almost 2 hours to dig out with my hands and a stick. It was my own fault for backing off the throttle right at the top of the drift.
You're talking about the fuel mixture screw. On a two stroke it is an air mixture screw. That screw should be pretty easy to play with, but I don't know how adjusting it effects the rest of the carbs adjustments.
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Old 02-24-2007, 06:18 PM   #5 (permalink)
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The screw does adjust the idle air/fuel ratio. It will make a small difference in the way it idles but not enough to effect the cold blooded nature.It will not change the way the motor runs past 1/16 throttle position. To cure the coldblooded problem you need to change out the 40 pilot to a larger. Most guys have luck with a 45. Factory recomended is .5-.75 turns out from seated position for the screw.

Also: on the old round slide carbs the fuel mixture screw was a air bypass screw and out was lean, in was rich.
With the newer power jet style carbs it is a fuel richening screw, out is rich.
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Old 02-25-2007, 09:44 AM   #6 (permalink)
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Mikuni roundslides I've got; on them the screw in question meters air. From what you're saying BeaverGrizz, I now know that on these CV carbs, it meters fuel. Thanks for this little tidbit; it's going to cme in handy.
Starky, you need a set of gun holders on your front rack with a shovel mounted there from mid-November, to mid-May. Tell your Missus that you've got a bitthday coming up...
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Old 02-27-2007, 02:08 PM   #7 (permalink)
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out (counterclockwise) is rich. I think it will make a difference. try 2 turns out from seated. Do not go more than about 4 turns out from seated, or you may have the screw fall out.
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Old 02-27-2007, 05:36 PM   #8 (permalink)
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Useable range for the idle screw is .5 to 1.5 turns out. If you must turn it in more than .5 to get it to idle, than your pilot jet is too big. If you must turn it out more than 1.5 turns than your pilot jet is too small.
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