this mechanical rpm limit is for protecting the enginge when at full throttle without any load.
Maximum power while cutting should be at a much lower rpm, like 9000 rpm or so !
Just "fixing" that valve will not affect the power while cutting! Excpet you will do some porting job, that ends up at a higher rpm during normal opperation.
The valve also does not alow you anymore to do carb adjustment according to max rpm, just as every rpm-limited saw, you have to do the finetuning while cutting in wood.
As I wrote in your other thread, the 143 is the last saw you want to tune above factory specs! Not very durable even in its original setup!