Honda copy engines

[swiftb]

Ive been offered a py90 pit bike/childs dirt bike for £65. Ive been told its in good tidy condition but has a running problem. Starts and runs ok upto mid throttle but when under load on full throttle it appears to be starved of fuel/lacking power - generally running poor.
As far as I know it has a 90cc honda copy engine. 3 speed semi auto 4 stroke.
Anyone know much a bout these engines? From what I can gather they are a generic motor and the 70/90/110cc share lots of parts etc.
Problem being I cant seem to find anywhere on the usual searches that sells parts for them. If anyone knows where parts can be easily sourced for these engines it would be a great help.
Im hoping the running problem is just carb related, so hopefully a fairly cheap fix. A good running bike seems to fetch around £120 on ebay so is it worth a punt for an otherwise good bike at £65?

[hmmmnz]

cmsnl will have parts for it or david silver spares,
i doubt its an engine issue,
it sounds more carb related
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[Dr. DaveJPS]

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