Wr 400 only starts with hot start and also wont idle at all

I was trying everything to start my WR 400 the otherday untill i pulled the hot start and it started but it wouldnt idle at all, could someone help? Thanks

You bike might be running rich. Check the plug as this should give you some indication. Is the filter clean. Also give the carb a clean including all jets and air passageways.

It could be something as simple as your starting procedure, or you could have corrosion in the carb creating a rich condition.


Did it ever run will with the jetting you now have?

I wouldn't expect the bike to idle particularly well with the hot start pulled, but it should stay running.  The single most common reason the older YZF/WRF models start hard is an improperly tuned carb, whether it's set up wrong in the first place, or just worn or dirty.  The most likely suspect within the carb is the pilot jet.  The metering orifice is extremely small; a #45 pilot meters fuel through a hole only 0.0177" in diameter.  If you develop even a .001" film of dried fuel varnish in that orifice, it reduces the effective size of the jet to that of a #39, which is enough difference to have a definite negative effect on idle and starting. 


I would start there. Something else that can come up suddenly is a crack or a broken off corner on the vacuum release plate on the engine side of the slide. When that happens the degree and nature of the symptoms the engine will have can be difficult to predict exactly, and they can act in all kinds of odd ways.

Hi thanks for the replys the bike wasnt getting no fuel at untill I pulled the hot start and it started and then I had too keep the throttle on to keep it running?

The hot start is simply a clean air bleed that bypasses the slide, and isn't any different than very slightly opening the throttle.  On the left side of the carb, there is a black plastic thumbscrew knob that raises or lowers the idle speed.  Turn it in (clockwise) to increase the speed and see if that helps. 


You do very likely have either an internal leak, a damaged VR plate, or a partially blocked fuel or fuel/air passage in the carb, however.

Hi thanks, it would only idle on choke and fuel screw wernt helping but my o ring for the fuel screw was perished and split so i used a slightly thicker one so I think thats why it maybe blocked, does anyone know the actuall size of the o-ring for the fuel screw?

Not immediately, but here's the actual part number: 3TJ-14562-40-00

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