110km/h and fading - Motorcycle-Journal Forums

NickGS500E · 01-05-2005, 01:23 AM

I've got a strange problem with my '90 GS500E; she'll sit on 100km/h (@5000rpm) all day long but if I try to hold her steady at 110km/h (@5500rpm) for more than a few minutes she'll shudder a little and then just start slowing down - won't respond to throttle at all - and just slow down to a complete stop and either just idle or cut-out (but start again straight away); the really strange thing is that I can ride off again straight away as soon as I'm stopped and she'll go back up to 100k's and once again just sit there without any stutter. It's almost like the engine loses rhythm but is fine once it finds it slows down enough to find it again. My mechanic thought that after he'd replaced the carby with that of a '99 model, the standard can with a (free!) straight through 56mm jobby, (he also pressure-tested her and it came up 165kpa in both cylinders which is apparently very good) rejetted and riched up the mixture the whole way through the range (thought it sounded lean) that it should be right (as my old carby was beyond dead), but I took her out for a short 700km's after all that and sure enough, she shut down at 110k's twice again but spent the rest of the day sitting mostly on 100 - unfortunately mostly very straight roads - without the slightest bit of trouble. I'm pretty sure it's gotta be heat related coz in mid-winter just passed I did Sydney to Byron and back (about 1700km's all up, 2 days up, 1 coming back) and she never faultered except for after filling up at a small servo just north of Newcastle - but the characteristics indicated bad fuel more than anything else. If anyone can offer any advice or thoughts on the problem that aren't too expensive - she was only $2000 to start with - it'd be much appreciated as the only thing I can put it down to is overheating or something cause mostly it's been above 30C when it has happened which, on an air-cooled bike doesn't sound as though it can be fixed except by not riding far or fast in summer - and who'd want to give that up!?
Thanks