New style can be run up to 500 but not for long. I do have a friend that has a son that ran Micros in a KT class and always ran at 500. They never stuck it but did eventually burn a hole in the piston.
Those are sure different numbers from what I use to run. I'm thinking maybe you just got them backwards.If your talking about a stock yamaha just run the wb3a that came with it. .045 fulcrum with no gasket, 10 psi pop off . Tune low jet 3/4 turn ,high jet 1 1/4 then tune high jet at wide open throttle on track and watch cylinder head temp 425f max gas fuel on new style head.
The text in the walbro article says to use a gasket, but the picture shows no gasket.Here is Walbro's document for rebuilding the wb3a as found on a number of web sites.
http://www2.idrottonline.se/ImageVaultFiles/id_469847/cf_359/Rebuild_Walbro_WB-3A.PDF (.045 w/gasket)
http://wem.walbro.com/distributors/servicemanuals/WBseries.pdf (says .04 to .06 w/o gasket)
Merry Christmas to all,
It's an open class but can only run gas. Can you really run them that hot?