How do you know when to move the clip on needle?

Just curious how you know when the needle is set too lean or rich, or if you need to adjust the fuel screw, or change jet? :D I'm trying to learn what the symptoms are that indicate which you need to adjust. Thanks. :)

Lots of questions-

The needle position dominates 1/4 throttle mixture. A rich condition will sputter when extreme or feel dull when slightly rich.

A lean condition will stall or hesitate near 1/8-1/4 throttle.

The pilot jet meters lower than needle diameter or clip. Your hanging idle is more related to fuel screw/pilot jet, but secondly can be affected by needle diameter. The blue needle has a richer diameter, which will help reduce a lean 1/8 throttle condition. The pilot jet and fuel screw are mostly for idle and closed throttle.


thanks :)

Hey James Dean,you sound like you know something about this. On both my CRF250 and my YZF250, if the engine is warmed up, even in neutral,engine idling if I crack the throttle wide or close to it , it stalls both engines. Is this normal? If not does this sound like the clip pos.? Would you think I need to go richer or leaner?


The bikes both need to be fully hot by riding them before testing. The idle speed needs to be near 1700rpm for the throttle to be snapped open.

The CRF has a standard setting of 2 1/4 turns out on the fuel screw (40PJ), so check that first. Try adjusting the fuel screw +/- 1/4 turn from there to evaluate the throttle response with the engine fully warmed. There WILL be a hesitation or stalling if the engine is not completely warmed. In most cases the throttle can be snapped open when the idle is set to the higher rpm limit (1800rpm).

The YZ250F ('04) has a bigger pilot jet(42) and will have the fuel screw closer to 1 1/2 turns. The same procedure should give quick response with it too.

In both cases, the stock clip position is where you should start. Check the fuel screw settings before jumping to the needle clip position and making changes. In cold conditions, the chances are you will want to jet richer on the needle clip position. In hot conditions a leaner clip position is more likely. If you take notes on each attempt, the record keeping will help identify what is going to work best on your bike.


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