Bclapham,the 324 does not offer enough piston cooling,the 537 does,then add boost to suit your needs.The 355 would have been safer to try,but the 537 is designed for 2 strokes.
PT cr said:Burgunder,
I am going to try leaning the main down from 440. I did have it sieze with a 430 on a sand track, but maybe the damage was done some other time with different jetting...
Sounds like it's time to start heading to 380-400.
Let me know what you end up with.
Parker