Hi i have a mc28, fitted with tyga pipes, it runs fine but at about 5000 revs it splutters through all the gears, can anybody tell me if this is normal behaviour!

Thanks

Are you using a PgmIII unit?
If yes, it sounds like an issue with the GPS system.
If not, check the carb needles, I remember there should be a washer underneath them that effectively makes the fuel mixture richer.
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Which could also make it too rich in the midrange and make it splutter .
Check battery voltage , clean carbs , put new plugs and try again .