I recently notice someone in MCN messing around with an old AR125 claiming it was worth a fortune because they'd done this and that. Truth is a used and abused AR125 would do well to fetch 100 notes from anyone in the know, heres why........
KAWASAKI AR125 1984 - 1992
Standard early models were about 20bhp but prone to seizure reguarly. They had the most unfashionable exhuast ever seen on a sports 125 that looked like it was from the seventies and finished in matt black. Later ones were restricted to 12bhp but fitting the older exhaust or filing bits out of the can which is very restrictive gives more power. Reliability is the trade off although 85mph wasn't a bad speed in the day. Looks like a mini GPZ900 so don't pay much and it's the slowest of the old school LC's.
HONDA NSR125 1992 - CBR125
Don't bother with older early ninties and eighties models as these bikes seemed to get abused more than any of the other 125's at the time. The 1992 model is good for about 95mph unrestricted and they seem generally reliable, should be quite a few good ones still around and are a cheaper to run alternative to RS and Mito 125's. Ended up replaced by slower more sensible CBR.
Suzuki RG125 1986- 90's
These were very quick, later models look like RGV's which still look the part today. Good for about 95 - 100mph, not many around now though probably a better buy than NSR.
YAMAHA RD125LC Early 80's
Can't have a 125 guide without the legendery LC. The first fast 125!! Good ones will do a ton unrestricted, handling will almost certainly need sorting, but it is THE CLASSIC sports 125 and the engine will take loads of abuse even unrestricted as long as it's kept stock and run on decent 2 stroke oil. May be on the expensive side because if their classic status but at the right price well worth a look.
YAMAHA TZR125 Mid Eighties - Mid Ninties
Evolution of LC with trick (for the time) Deltabox frame, clean early ones still look smart with a full fairing. Good for the ton and hugely reliable if looked after properly. Late bikes had 250 frame and fatter tyres but weighed a bit more. My weapon of choice!!
CAGIVA MITO 125 1991 - NOW
Early ones were supposedly a Lawson rep, but in 1994 they looked like the then new Ducati 916 which is reason enough to buy one. Comes with 7 speed box high fuel consumption (for a 125) and heavy servicing. Top end rebuild at 10,000 miles as part of service schedule!! (TZR's have been known to clock 40,000 miles before any rebuilds needed). Good for the ton although some owners claim speeds upto 115mph, but I've yet to see it when following them.
APRILLA RS125 1991 - NOW
These are probably the most popular 125's at the moment, appart from styling and a catalytic converter they havn't changed much over the years. Engine is barley any faster than TZR, but they often have a huge gap in the mid-range and require lots of clutch slip. Cheaper on fuel than Mito, but still big service costs with engine rebuilds every 10,000.
Hope this guide helps someone looking for a used sports 125 who's on a bit of a budget. Don't let someone con you because they've wasted money on some old crap and want to pass on the cost. I'd buy super cheap, then budget for an engine rebuild and a bit of chasis tlc with bearings etc. The Yamaha's are by far the least likley to go wrong and are not shabby on the performance side of things either. Don't bother with AR's and other really crap bikes unless they're given away, they were much cheaper than the rest years ago and only sold to those that couldn't afford the better kit. I know because I bought one.