I didn't have any such problems with my 1251, but have seen others. I'd say the core 5008 is certainty going to draw less power from your BEC and should work better with the Spektrum receiver. Lighter too.
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Team Yokomo - YZ-2CAL3 | YZ-2DTM3 | YZ-4SF2 | YZ-2T | YZ-2DTM Worlds | YZ-2DTM x2 | YRX-12 x2
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10electric | Batley Buggy Club | YORCC | RHR | MB Models
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