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Pilot screw seating

2K views 5 replies 6 participants last post by  Jrbell76 
#1 ·
Hey all,


I have cleaned my carb and replaced jets. No modding, just a new set of jets. I am confused on the seating of the pilot screw. People say, screw it in until it is softly seated and then back it out 2.5 turns to start. What is softly seated, as I am screwing it in, what feeling or clue am I looking for that tells me it is softly seated, vs overtight? Thanks in advance.
 
#3 ·
The pilot screw is set at the factory using an exhaust analyzer and may or may not be 2.5 turns open. 2.5 turns pretty much guarantees that it will run and allow proper adjustment. If you have a colortune plug then adjust as follows. Get the engine at running temperature and at idle. Close the pilot screw until you see a flicker of white (lean). Open the screw until there is no white. Install new plugs and ride the bike about 15-20 miles and pull the plugs and look at them. You are looking for a light brown or grey color on the plug enamel. If still white, open the pilot screw about the width of a dime. Continue this process until you have a nice light brown or gray color on the plugs. If you do not have a colortune plug, start with the pilot screw at about 1.5 turns and make the adjustments. I have a 4 cylinder, 4 carb Yamaha and 2.5 turns open is the standard starting point. But using the above process my pilot screws are set between 1.75 and 2.25 turns--each carb is a little different.
 
#4 ·
The idle adjustment screw has a slightly tapered needle tip.. if not lightly seated tip is jammed into aluminum passage of body.. the brass tip of idle screw has been known to twist off plugging passage if over tightened..

 

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#5 ·
Go easy and be gentle screwing it in till it stops, that is "lightly seated".
back it out 2.5 turns.
adjust the throttle stop screw till its just barely making the bent/crooked/dogleg linkage-thingy touch the accelerator pump shaft.

put on one of them external tachometers where you wrap 3-5 turns of an antenna wire around one of the spark plug wires. ($20-25 on amazon)

warm the bike up good and warm.
turn the idle mix screw in till you see the rpms drop, then back it out, watching the rpms go up, and stop at the point where the rpms don't go up no more.
adjust the idle stop screw so the tachometer reads 1450 rpm.
turn the idle mix screw in and out a bit, trying to find that just max rpm point again.
adjust the idle stop screw to get 1450 rpm again
then turn the idle mix in just a bit to get the tach to drop to 1400 rpm and you're done.
 
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