Large amount of coolant coming out of overflow

Hey guys

I recently bought a yz400f and dont much about these bikes. I noticed when it's idling, it seems to me that a lot of coolant comes out of the overflow. Once started it's only a matter of seconds and coolant starts coming out of the overflow. Do these bikes warm up that quickly. After an hour of so of riding i needed to put in 1/2 litre of coolant or a fraction less than 1/2 L. Is this normal with these bikes, it does not seem to leaking anywhere else.


The second thing is my bike starts with no choke when its cold. I have never heard of this and researched some of the sticky forums. It may be too large a pilot valve, but i have not pulled the carb apart to check it yet. It runs fine for a while and then idles inconsistently (high, then low and stalls). I put in a new plug and it runs fine again, but when i check out the plug does not appeared to be fouled, it is a little sooty but not wet.

4 strokes dont like to idle for long. i know my 450 will puke coolant if i have it sitting at the line long enough.

it could have also been overfilled. once the coolant is above the fins theres enough coolant, atleast thats what i was told

Check the cap....and maybe use different type coolant....

Sounds like you need a new head gasket. If someone has been in there and replaced it the probly didnt torque it properly. Had the same problem with a friends 426 2years ago. Put a new head gasket in and torqued it properly never had another problem with it.

Sounds like you need a new head gasket. .


Try some ENGINE ICE that stuff works wonders...

My 01 WR426 has been leaking coolant due to overheating since new. I spoke to many mechanics and including OEM folks and the all said it was normal. It is only when Idling right? Get moving and the problem goes away?

get a compression tester and run the motor up to Top Dead Center and see if you have a leak. If it leaks off at a fairly quick rate you need to look at the head gasket. You can try putting a different cap on, like a 3.5 lbs insted of the 1.1. If it just blows the coolant out at an idle with that cap you can be almost certain its the head gasket.

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