In April ’87 I was looking for a 125. So I was pleased to see an advert for a Yam RD125 for only £280. But, alas when I arrived at the owner's flat I discovered that it was not an RD but an RS. The difference being a mere matter of one cylinder. Oh well, the bike was quite tidy except for a torn seat, dented front mudguard and the odd patch of rust on the frame. It had only 6000 miles on the clock and as the owner was a trainee policewoman I had no reason to disbelieve this [You have much to learn, grasshopper - 2021 Ed.] After a painfully slow test ride on the pillion (I think we did 29mph at one point) I decided to buy it. I made an offer of £240 and this was accepted.
A week later I picked up the bike and rode it the 20 odd miles home. Not having ridden a bike for a while, the first few miles were tentative but I gradually gave it some welly; on the home straight I saw a disappointing 67mph - yawn! The reason for the lack of speed was revealed when I stepped off the bike once home. When the engine was revved sparks and flames erupted from the end of the exhaust. It had obviously never been decoked or run up to its correct operating temperature.
So the first job was to clean the shit out of the exhaust. The exhaust and baffles were soaked in petrol and ignited. The engine was decoked and the head gasket chucked away to increase compression. With these mods the bike was finally able to hit 70mph.
The horrible chrome back mudguard was chucked and the rear light and indicators relocated. Drop bars were fitted so that I wouldn't look quite so stupid with my head down on the tank. The bike was thrashed along for a month in true boy racer style, making the daily 22 mile trip to college, until I became terminally bored with the performance.
I bought some Hytech reeds for £9.95 and S&B filter and jets. I was led to believe that these would improve performance, but they merely made the bike sound better. I raised the gearing by bunging on a 14 tooth engine sprocket, this finally allowed me to hit 75mph. Being an art student I decided to restyle the bike. So off to Halfords to buy some GRP and spray paint. Using part of a bucket as a crude mould I soon fashioned a tail unit which I bolted in place. The bike was resprayed white and red based on a TZR.
To match its Team Yam colours all the bike needed was even more performance. An illegal Allspeed was thrown on. This gave a large increase in both performance and noise. The bike could wheelie in first and run to 83mph in top gear. The exhaust port was later raised 1mm and the bike did 90mph with a tail wind on the flat. I then decided that was as far as I was going to take the tuning. My mind returned to the styling and a TZ125 seat was ordered, its delivery coinciding with the postal strike.
I've had no major problems with the bike, the most serious was when a lead from the rectifier came loose and every (eleven) bulb on the bike blew. When the original tyres wore out I replaced them with Metzelers which the dealer who fitted them blew up to 40psi. I crashed on the forecourt of the garage where I was going to check the pressures, after a massive front wheel skid.
One day after removing the front mudguard, I was surprised to find brake fluid splattering over my visor as I watched the caliper bouncing down the road. In my infinite stupidity I had forgotten that the mudguard bolts also held the caliper in place! Luckily the caliper was undamaged but the hose had been torn into three pieces.
The next amusing little problem was the lemming like rear light lenses which would throw themselves off the back of the bike, under the wheels of any following traffic. Even Superglue on the threads and screws didn't help. So I chucked the old unit in the bin and fitted a Smaller motocross unit which is both brighter and prettier. I added a home made front mudguard to the front forks, which sprayed water straight onto the HT leads. I couldn't go more than 5 miles without stopping to spray the lead with WD40. I eventually gave in and fitted a NGK plug cap which solved the problem.
I became fed up with the ear shredding noise from the S&B filter so went back to the stock box with smaller jets - solved all the problems without a power loss and improved fuel economy to 65mpg, ridden hard. In standard form the bike was well mannered with usable power all through the rev range and a surge at about 5500rpm. In its tuned state the power runs from 6500 to 9500rpm, the bike is particularly apeshit between 7 and 8 grand.
The acceleration is very Impressive at this point, if dropped from 4th to 3rd in this region the bike will lift ‘the front end and leave ‘everything in a cloud of hot blue smoke. The handling and high speed stability are fine but when pushed hard around a corner with an adverse camber, the rear end can slide a couple of inches. I've grounded the footrests on both sides... it's very easy to write off the RS as a boring commuter, just another two stroke single, but there’s lots of tuning potential and it handles alright on decent tyres. The perfect street sleeper.
Alexis Cousins