88-91 cr250 powervalve Q

hey guys,

any cr250 experts out there? recently rebuilt my 89 cr 250, fresh top
end, when we did it i was told to grind the power valves way down, like
3mm behind the cylinder wall surface, im having low end power issues,
im kinda thinkin they didnt or shouldnt be ground that far, if anyone
can offer advice thanks, ive checked the carb float / jets / plug etc,
also if anyone has a set of power valves for a cr sitting around i
might be intersted in buying them, also a aftermarket pipe etc.