Suzuki gs125 (1999) question

[Tonyg1987]

My brothers gs125 is having some problems, it is losing power and cutting out in higher gears (4th & 5th) and also backfires when decelerating. I've read that this can be down to the fuel running too lean or rich. I've taken the spark plug off to examine it and there is no discolouration at all, and I'd like to adjust the air pilot/ fuel screw but I can't seem to locate it on this bike....can someone help me. Also if you have any idea what else it could be I'd appreciate it.

[Cheeseybeaner]

I'd start by changing the ht lead and plug cap then maybe a plug if that doesn't help. Made a huge difference to my girlfriends one which was having the same issue as yours, it suddenly became a lot more poky!
If you have the manual it may be worth checking the float height and adjusting if necessary, after we replaced the detereriorating float the one which was in the bike was set quite differently to the NOS one we fitted which it ran a lot better on. Obviously you may have a sticking needle valve too, removing and cleaning the carb would be worth doing. Pilot screw settings are only for low speed running won't affect things higher up the rev range.