I brought a 99 suzuki katana ay50 and waz told that it needed new piston rings but my mechanic friend beleaves it is a carb problem because the bike only runs well when you choke the carb with your finger any help or opinions would be greatly appriciated

Question edited for a lot more clarity.

BTW it isn't a Moped because it doesn't have pedals 'Motorised and Pedal operated - 'mo ped'. It is a Scooter.

Here is your service manual. Check all connectors for corrosion, check fuses and grounds on the lights. It may be a voltage rectifier issue. Probably need a good electrician.

Suzuki AY50 servicemanual

Scootergrisen https://scootergrisen.org > download > suzuki_a...
This manual contains an introductory description on the SUZUKI AY50/50W and procedures for its inspection/service and overhaul of its main com- ponents ...
268 pages

SUZUKI AY50 SERVICE MANUAL Pdf Download

ManualsLib https://www.manualslib.com > ... > Scooter > AY50
View and Download Suzuki AY50 service manual online. AY50 scooter pdf manual download.

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it sounds like there is a bad wire or a bad ballast, if you are using halogen bulbs than you should remove the conversion kit and go back to the regular oem harness.

It's likely a broken piston ring, worn out piston rings, or faulty valve seal(s)... However, it could easily be some other thing... like crankcase ventilation valves, lines or hoses...cracked block... I know.. I'm not being much help... but, a good mechanic can probably zero in on the problem...

99 gsx suzuki katana is oil cooled, does not use water. In front of your bike is a small radiator that's your oil cooler.

C HECK PISTON RINGS AIR FILTER FUEL LINES GAS LINES ETC.

That is the carb overflow, Which means that the float is probably sticking. The carb needs to come off,and be thoroughly cleaned.

Check the battery voltage when the engine is running. It sounds as if the regulator has failed. Also check the earth lines on the bike and make sure they are tight and clean.

replace the fuel
clean the carbs
change the oil
new plugs
clean air filter
check the valve clearances( if any are really wide a valve may be stuck open)
I assume you have already fitted a new battery

a top end kit consits of a 1x piston 2x circlips 1x gudgeon pin 1x set of rings and 1x gasket set basically you take the carb off take the exhaust off take spark plug cap off undo bolts on head/barrel remove gasket slide the barrel off removing bottom gasket then take the circlips off 1 side then push the pin through i put a piecwe of card bord or rag in the crank to stop **** falling down through when you slide the pin out the piston will come out then you will see a bearing in the con rod leave that in there then get new piston put ciclips in one side then get the gudgeon pin put some oil on it and put it in place of the little bearing the push the pin through and put the circlip in and then put the rings on then in the ring gap you will see a little pin the gap in the ring goes in beetween that little gap then you put the base gasket on then inspect the barrel if there is dips in the lining re hone it or get some glass paper and rub it till its smooth but not too much or it will rub down to much then rub some oil in the barrel then put the barrel over the piston and compress the rings and slot the barrel down the pistonand put head gasket on and put head on and tighten bolts/nuts then replace carb good luck

Idle issues can be fuel/air (mixture ratio) or igition (spark strength). It sounds like an air restriction issue. If there is no blockage throught the air inake/filter, make sure you adjust the jets to specifications and make sure there are no float issues with the carbs.