Dave, I'm not sure it's possible for you to have goofed on the fuel mix enough to cause that sort of drop in performance, unless maybe you reversed the kero and castor proportions. (You are measuring by volume not weight, aren't you?) If what you've got is even remotely similar to the proportions stated at the start of the thread, it should run fine. I don't know about 'goosing' the mix, either, since adding an arbitrary amount to an uncertain quantity is reallly just stabbing in the dark and may just be a waste of good ether and Amsoil. Even if it worked, you'd have no idea of the actual composition that was now working for you. In any case, a shortage of ether or DII isn't ever going to cut rpms by nearly 50%. If it started ok, you've probably got a sufficient amount of ether.

While it's hard to say without being there, 'sputtering at low rpm' sounds like it might be very rich (regardless of what the needle setting was last time). If it starts ok and isn't labouring, leave the comp where it is for now, and see if you can lean it out slowly.

What sort of 8x4 is it? Just curious, since 12000 is still on the low side for a decent 2.5 on that size prop.

Steve