Leaky coolant - this one is driving me crazy!!

Ok dudes,

I've got a 99 WR 400f and a while back I sank it in a big waterhole and sucked a bunch of goo into the breather. Lesson learned. I took it straight home, changed the oil a few times and then it started smoking badly. I figured the valve seals were hooped, so I took the motor apart and replaced the valve seals. I also replaced the rod as it was slightly worn, main crank bearings and numerous bearings full of grit. The top end and cams all looked excellent so I left well enough alone, with the exception of new rings. I put it back together and it started up on the 2nd kick and ran very well. Then I noticed that after a few minutes of riding (still the break-in ride) it was spurting a bit of coolant out of the overflow tube. I have removed the overflow tank, but it is not overheating, just spitting a bit out every now and then. Seems like somehow the cooling system is getting pressurized and forcing the coolant out.

Thinking that my head gasket wasn't quite sealing, I pulled the head again and replaced the gasket, ensured the surfaces were clean and re-torqued everything to spec and tried it again. Still puking out the overflow.

Anybody hear of this happening and what do you think I should look towards from here? Spring is coming and I don't want to miss another season....

Any ideas are welcome on this.

Thanks

did you check to see if your head was warped

replace the radiator cap, if that fails get a cooling system pressure test done.

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