Xr400 fuel screw

Hi ya all, been a while.

I've got a question for the experts out there, why would my xr4 keep running if i wind the fuel screw all the way in?

Shouldn't it die?

What is this a sign of?

Could this be a sign of a missing O-ring from in there?

I have had the screw out and nothing has come out apart from the spring, the O-ring may be jammed up in the hole but with a casual look i can't see anything that looks like an O-ring.

If it is missing should i replace it, would it cause this issue?

Carb is the standard Mikuni btw.


So the stock carb on an Australian model is a Mikuni? In the US it's a Keihin.

Besides the spring, there should be a washer and an o-ring. If the washer is stuck up in there too you won't see the o-ring.

Running the screw in all the way won't necessarily kill the engine, it just leans the mix and makes it run poorly.

hey rideorberidden,

Its coopz from over at DBW,

are you sure its a mikuni, arent they a kehin?

Atleast the 250 is a kehin?

Take in what these guys have to say, they are all VERY knowledgeable when it comes to XR's

Have fun!

Ahh yep my bad, it is a Kiehin, it used to have a pumper Mikuni on it but that's gone now...

Turns out it's normal as stated above, it will just lean out heaps but not necessarily kill the motor.

Thanks for the replies.

Mine runs still good with fuel screw all in, I think it's because the pilot jet is a bit too large (I have the stock keihin and my pilot jet is a 60, I am at sea level and my bike has only the "gordon's mods" on it)

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