Yz400f carb problems

So I went riding last weekend and the carb started leaking gas every where thinking it was just dirty I took it apart and cleaned it all and made sure all o rings were In there proper place but the leak is still happening and now the bike starts will run for 10 mins then it seems to flood out but the needle valve seems to be in good working order and the floats don't have any holes but there is one strange thing going on before when u twisted the throttle a little stream of gas would shoot into the motor now that doesn't seem to happen not sure why Any help would be great thanks guys

Sounds like the accelerator pump diaphragm ripped.

There no rips or damage so I am unsure what the issue is I am going to take it apart tn and have another look

The carb does have to be full of gas for the accelerator pump to work.  Just to be sure we aren't overlooking the obvious.

Thx ya I don't no it seems to fill and over flow but te needle valve seems good that's what I don't get and I wonder if the bowl won't seal could that cause it not to work

So up date I got the bowl to seal on the carb now but the bike is still flooding out and this time after trying to start it I took the tank off and kicked the bike over with just the gas that was in the carb it fired up and ran fine so I tried hooking the tank back up to see if it would run and it flooded out again . So I removed the carb and when i took the bowl off to look at what was going on there were no signs of problems I really don't know what to do here . The only possibility was the O ring on the needle seat looks pretty bad any help would be awesome thx guys .Here is the mods the bike has on it if it might help FMf exhaust wisco hi compression piston stage two hot cams and a stroker crank all done this season

Sounds like a bad needle valve. The tip gets a very slight ring in the rubber that allows fuel to pass. I'm not sure on your bike but there may be an o-ring that has failed on the seat.

Thx slow and ya I am bringing the carb in tm to see what's up with it

Ok so I took it apart one last time before I was going to take it in I got the accelerator pump working if that pump wasn't working properly would that cause the carb to over flow

No.  It would cause a fuel leak if the diaphragm were torn, though.


With the float bowl off, and with the gas line connected, raise the float up gently against the float needle to the point where the needle stops rising.  Turn the gas on.  The needle should hold it from leaking.  If it does not, remove the float, cover the hole in the needle seat with your finger and try again.  If it leaks without the float in place, the O-ring on the needle seat is shot.   Leaking with the needle in place after the O-ring is replaced means that the needle and seat need replacing.

Ya I tried holding the floats up and no leaks but I won't be able to try the carb on the bike till Friday it was also wondering if the carb was on a angle that would cause it to over flow this is my last attempt before I take it in when I saw the the accelerator pump was working again I got excited hopefully all goes well thanks guys tho your input has been very helpful

And was wondering if anyone could give me any ruff numbers for hp gain on my build it feels a lot faster but unsure how much of that was gained threw mods or just from a new top end thanks guys

Hey guys problem solved it's running great again thanks so much for the help

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