Issues after ninja 250 major service

[Reedy]

Recently I had my 08 250 in for a major service and when I got it back there was a rather large noticeable degradation in performance. I took it back to the bloke, who has been amicable about trying to fix it but the problem is still there. Initially he said the standard major service things were done and 8 of the valves were shimmed. I also got new tires for it. I took it back, cos it was running laggy and he said he put carbie cleaner through it but it still doesn't have as much pull as before the service.

Its got an after market exhaust, a high flow air filter and the needles have been raised in the carbies but I can't see what happened to cause a lack in power when it was serviced. The bloke says it may be because its running too lean and wants to try a stock air filter in it... but it was fine before and he said he's adjusted the mixture screws..

I'm basically out of ideas, apart from the rear brake rubbing after the tire change (blah) and i dont want to start ripping it apart after paying 900 odd bucks.

Im pissed about it but I just want to get it back running the way it was before or better , could anyone offer any suggestions (i know its hard guessing from the information given) as to wtf could be wrong here ???

Thanks

[mike-s]

first thing i would do is a spark plug chop test.
link 1, link2, link3, link4. Now get reading.

[oldman]

New tires are larger than worn tires and on a 250 that might give you an indication of less performance as it effectively makes the gear ratio higher. The mechanic shimmed the valve buckets, did he do it right, check the compression. Carbies could be farked but the idle screws usually don't affect upper RPM performance. Did you go off your diet or quit drinking during the service? An added bit of weight or sobering up will both give the appearance of degraded performance. Just as too much or too little Jim Beam will either make your lady happy or make her wish she had gone home with that other more sober, (or drunk) bloke.

[Reedy]

Thanks guys for input.