Yes, I agree with you both,
Every bit of negativity adds up to achieve tipping point,
A lot of big bore four stroke AIR COOLED 500s run way too hot and don't take much to reach the tipping edge of safe temperature. Excessive temperature rise is a domino effect, especially when under duress. Racing. Load.
Part of a tune is to select coolest plug on the day that will still match the running performance of the hot plug choice one next to it.
A tappet clearance when cold does not mean an exhaust tappet clearance when normal running temperature
has been exceeded, particularly with lower end metallurgy.
There is more than one consideration to setup an exhaust valve so its head runs cool.
A couple of things; the head of an exhaust valve should sit proud of the seat, not sunk into its seat. The guide wear should be within spec, so when it snaps shut it doesn't leak because it vibrates/shudders on close.
The set up is more critical for AIR COOLED already running too hot engines.
There would be a lot you could do with the shell of these engines with components made from modern materials.
I doubt the selection or consistency of Indian metallurgy and their desired rates of thermal expansion in valve stems for example would meet the harsher upper end of race demands. Etc. Etc Etc
Most of the population would not be aware of how much the fuel quality varies in this country. It varies a lot.
Short story, BP98,,, it was the most consistent value for money,when I was a part of the industry.
I hope it still is. Best bet, BP100 if you can get it and justify its expense.
The higher the state of tune, the greater the demand for fuel consistency.
Fuel inconsistency is more detrimental and a much bigger issue in air cooled carburetored four stroke engines than it is to modern liquid cooled engines that are computer controlled and ever increasingly designed to be self compensating systems.
