Fuel Mixture Screw Setting - Yamaha YFZ450 Forum : YFZ450, YFZ450R, YFZ450X Forums
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post #1 of 4 (permalink) Old 12-17-2003, 08:05 PM Thread Starter
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Join Date: Sep 2003
Posts: 205
I have the zip-ty screw and I have turned it back and forth until the machine idles the fastest. Is this the correct procedure?

I run 170main, GYTR Needle on 3rd clip and 45 pilot. I had the 48 pilot in but I could turn it all the way to 0 turns and it would still run. I was told that means the pilot is too rich. Thoughts?
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post #2 of 4 (permalink) Old 12-18-2003, 03:18 AM
Join Date: Nov 2003
Location: Corona, Ca
Posts: 80

The pilot air screw and pilot jet affects carburetion from idle to around 1/4 throttle.

The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle.

The main jet controls fuel flow from 3/4 thru full throttle.

The pilot air/fuel mixture screw can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. On our carburetor, the pilot screw is located in the front of the carburetor, which regulates the fuel mixture. The mixture will be leaner if it is screwed in and richer if screwed out. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs. You should be somewhere between 2-4 turns.

I have airbox lid off, baffle out, GYTR jet kit: 165 main, 45 pilot jet, 4th clip on the needle, and 2 1/4 turns out runs great. Took a couple of hours to get it right, buy running up and down the street. The key is to check the spark plug each time. Black too rich, white too lean. Every YFZ450 is different so try only one change to the carbuertor at a time. Goodluck. I mainly ride at Glamis. Elevation: sealevel.

How do like the zip-ty screw? Easy to use and to get to the pilot screw

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post #3 of 4 (permalink) Old 12-18-2003, 07:28 AM Thread Starter
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Thanks scandal!

I love the zip-ty screw as it is much easier to adjust while the machine is running. You have answered my ? and I believe may be the problem with my off idle stumble.

I was not sure if I should run the machine to test the fuel mixture screw settings but rather just set the idle to the highest position. If I move it from where it is now it will lower the idle but may get rid of the hesitation. Thanks again for your help!

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post #4 of 4 (permalink) Old 12-18-2003, 03:28 PM
Join Date: Nov 2003
Location: Corona, Ca
Posts: 80
anytime, just check your spark plug after each test run to see if your running lean or rich at idle and 1/4 throttle

goodtimes :evilgrin :D
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