shut off at high speeds

[spicciani]

I am having a issue and I would love to call on yalls wisdom.

my gz250 is stalling at high speeds(70mph ish) engine cuts off as i roll off the throttle then the bike dies . After a few minutes it starts right back up again . I bought the bike two weeks ago and I have cleaned the needles in the carburetor , changed the oil and filter.

one issue that might be related , is that when i am accelerating ill be in the power band and then loose it , then get it again .

the bike came with what I guess might be a ebay pipe that back fires and might not have a baffle.