derbi senda sm 50 cc 2004 --bike splutters

[mjhalifax]

hi
can someone help,my son has a
derbi senda sm 50cc--he bought it over a year ago, when he rides it normally it rides great, but when he puts full revs on it seems to splutter, its done this all the time hes had it

hes now looking to sell the bike and needs to sort this problem out,

it has been deristricted by the other owner it has a aftermarket air filter it has a technigas exhaust it reaches speeds of 55mph,

if you rev it when the bike is standing still it seems fine,
the carb has been cleaned and still the same
please help

[bladerunner]

Without knowing if it's been jetted properly be worth checking if it runs better flat out with the choke on..if it does it's probs running lean...if it runs worse then it's too rich and if it makes no difference..time to look elsewhere for the problem
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's