Randy...trust me sir, I heed your advice a LOT..
When I was breaking in and re-learning how to fuss with these Fox engines ---I noted that the 10% N and 15%N fuel gave me a much broader and easier to set needle
That's definitely true. It's much *louder* as well. I wouldn't even bother with 5% any more. Heed well the caution about 15% and higher - unless you have a Randy super-crank, you are going to break one eventually.*
But at least for stock engines, adding castor can sometimes act like adding an equivalent amount of nitro. I am not sure why, maybe it cools it better so you can run it harder, or maybe it fills up the gaps and improves the compression, but it can be very effective. And even on the engines with most of the internal parts replaced, you still use the same conrod, which needs lube. I am less convinced about the bushing, they seem to last a pretty long time, and you want it to be pretty loose, because IMHO, you need it loose to get clockwork 4-s breaks. I have seen people retire engines or get new crankcases for bushing wear that I thought were just getting right.
Brett
*I got a PM not too long ago accusing me of shilling for Randy, partly because of the discussion of the high-zoot Fox 35 crankshaft. That's absurd on several levels (since I spend a lot of time on Randy's poo-poo list for various possibly-justifiable reasons), but the super-crank definitively resolves both the breakage issue, and usually/frequently greatly reduces the vibration over the stock crank. I think it's more then the counterweight, since plenty of people have added tungsten slugs to stock cranks without having much effect. I think the stock cranks are frequently eccentric or crooked, and Randy's are straight.