Homemade Supermoto

I bought a made-in-Japan 1993 XLR250R in November 2008 to use as a commuter bike, and replace the XL250 Degree I had used for the previous 2 years.

Honda XL250 Degree

Honda XL250 Degree

Honda XLR250R in the shop

Honda XLR250R in the shop

The XLR had no signs of use and very low mileage. It’s a high quality bike – unlike it’s sister the XR, it has a PD79 slide carburetor with an accelerator pump, so there is surprising snap available even from a 250. The headers are high quality and show no signs of corrosion even though she is now 20 years old and has over 30,000 miles on her. The front forks are Showa cartridge types, and the rear is a fully-adjustable Kayaba with a remote reservoir. She weighs 115kgs, and with a full tank and a box on the back, she’s 128kg. There’s 28ps (27.6bhp) and 2.5km torque. The product page is here.

Unfortunately, many XR250 parts won’t fit, so even simple things like the clutch cable are different.

Main Specifications

Common name XLR250R
Model Honda MD 22
(M) Overall width × height × length 2.165 × 0.860 × 1.210
Wheelbase (m) 1.430
Minimum ground clearance (m) 0.285
Seat height (m) 0.860
Wet/Dry Weight (kg) 125/114
Seating capacity (persons) Two
(Km / L) test value fixed area traveling 50km / h fuel consumption rate 50.3
Minimum turning radius (m) 2.1
Engine Model MD 17 E (single-cylinder four-stroke air-cooled valves · OHC · 4)
Total displacement (cm 3) 249
Inner diameter × stroke (mm) 73.0 × 59.5
Compression ratio 9.3
Maximum output (PS / rpm) 28/8, 500
Maximum torque (kgm / rpm) 2.5 / 7,500
Carburetor Model PD 79
Starting method Kick type
Ignition device format CDI ignition magnet formula
Lubricating method Combination formula splash pumping
Lubricating oil capacity (L) 1.6
Fuel tank capacity (L) 9.0
Clutch type Wet multi-plate coil spring
Transmission format Constant mesh 6-speed return
Transmission gear ratio 1-speed 2.769
2-speed 1.941
3-speed 1.450
4-speed 1.130
Fifth 0.923
6-speed 0.785
Reduction ratio (primary / secondary) 3.100/3.125
Caster / Trail (degrees) (mm) 26 ° 50 ‘/ 105
Tire Size Before 3.00-21-51 P
Later 4.60-18-63 P
Brake type Before Hydraulic disc
Later Hydraulic disc
Suspension system Before Telescopic
Later Swing arm (Pro-Link)
Frame format Semi-double cradle

I tarted her up a bit and she then looked like this :

17-year old Honda XLR250R

17-year old Honda XLR250R

After my KTM was stolen, I decided to convert the Honda to a supermoto. This is what it took….

Wheels, Gearing, Speedo, Mudguard and Sidestand

First I sourced some 17″ wheels from a Honda XR250M. They fitted exactly :lol:and that saved a lot of trouble.

The original sprockets with the smaller wheels meant the gearing was great for acceleration but fuel consumption jumped from 20 miles a litre to 16, so I changed the front and rear sprockets to re-gear the bike from 16/50 to 17/44. It was hard to find parts because the chain is the lighter 428 instead of the 520 on XRs. XLR250r gearing is an xl file calculator to work out the effects of gearing changes. The new gearing is still fine for walking speed in first without slipping the clutch, and sixth gear gives about 5,000rpm for 60mph so highways don’t feel like I’m thrashing her. 

The front sprocket is still the standard one (JTF264) but with one more tooth – it just fits. The new rear sprocket, a JTR469 for a Kawasaki KE175, 428 chain and 44T, didn’t have an indent like the original. So I had the rear sprocket hangar machined so the new sprocket was 2mm closer to the wheel, the same as the indent would be.

She now does 22 miles a litre or 100mpg. Amazing. I might switch back to a standard 16T front sprocket when this set of chain and sprockets are finished. These are the dimensions of the original sprockets, although the first says 18T instead of 16T. This website is great for finding sizes http://www.jtsprockets.com/

xlr250r front sprocket xlr250r rear sprocket

The wheels lowered the bike so I also cut the side-stand shorter and fitted a big washer on the end, so the sharp end doesn’t sink into tarmac. I got a supermoto front mudguard, and made a chain guard from some box aluminium. I replaced the front brake hose with a braided steel one.

Of course the original speedo is designed for a 21″wheel so I had to replace that too. I found a cheap Koso display and fitted that. That needed a regulator circuit to power it with DC12V, and also a battery back up so the memory chip could store the mileage immediately after the engine was turned off – it needs power for about 3 seconds. For the DC 12V, I used a bridge rectifier rated for 4 amps to create DC, and this is regulated to 12V by an LM2596 I got on Ebay.

The battery backup uses an 8.4V 680mAH lithium rechargeable battery with its own 500mA lipo charging circuit connected into the circuit through diodes to prevent charging/discharging problems. The display uses about 120mA in use, and 6mA when turned off – for the clock. The battery is small and light and gives enough juice for the clock to keep the time for four days without use and needs just over an hour of use to fully charge from empty.

However, getting the display’s LEDs to work was more trouble than they’re worth – they’re not very bright, so I also made a custom plate with bulb holders and lenses to house the idiot lights. The fuel gauge is not real – that wire is shorted to ground so it says the tank is full. If not, the bars would flash and that’s annoying. The display also has a temperature gauge so at some point I’ll hook up a thermocouple and see if I can get that working. The speedo reads about 10% over the actual speed.

Koso Display and idiot lights

Koso Display and idiot lights

Fuelling and airbox.

I re-routed the crankcase breather through a separate filter instead of the airbox, so the airbox pressure is not affected by the engine, and plugged the airbox outlet for this. I removed the airbox intake restrictor so it can breath more, and I fitted a K&N air filter. I also added a round hole in the side panel as an intake, with a tube to reduce induction noise.

I changed the exhaust to a Supertrapp, which is 1.2kgs lighter than the stock unit, but it is really loud and doesn’t add much power, so I modified it with a dB killer and better filling, and drilled a 1″ hole in the centre of the exhaust end cap for better flow and a better exhaust note. I re-jetted the carburetor so it runs a 38 pilot and 138 main. The plug is light tan and there’s no surging anywhere, with only slight popping when decelerating on a closed throttle.

Ignition.

I removed the resistor in the spark plug cap and fitted an iridium plug with a built-in resistor, DR8EIX. I also added a bridge rectifier and capacitor to drive a 12V horn, instead of the weedy AC piezo tweeter. I added a 12V red 20LED strip at the back as an extra brake light.

Suspension.

I removed the 70mm off-road springs in the front forks and fitted steel tube spacers to stiffen the front suspension. I changed the rear suspension linkage to a Devol link for an XR250,  with standard Honda bearings fitted into it, and this lowered the rear and re-balanced the steering somewhat – the link dropped the rear 38mm. After this, it took some time to get the bike set up correctly. The rear link makes the rear softer so the pre-load must go up. This puts more weight over the front, but this was not enough and steering was too slow.

So I started raising the fork tubes through the top yokes and adjusting the rear pre-load to get a balance. It’s not very scientific, but for my 80kgs weight sitting halfway back on the seat, with a 4kg load in the box and a half tank of fuel, I like the fork tops about 8mm above the top yoke, with pre-load to suit. The bike steers quickly but is stable on straights and through corners.

So, she’s all set up and handled really well. :worthy: After the Dunlops in the pictures wore out, I replaced them with BT45. It was a bad idea and the bike was not much fun to ride on such tough rubber. So I’m running a Bridgestone S20 front and a 003RS rear now and they’re excellent. It can carry really high corner speed and flicks through twisties beautifully. The only thing I haven’t done is raise the foot pegs – I can get them to scrape but only when the bike is almost at full lean so perhaps there’s no need. She’s a commuter bike after all.:banghead: One final job – I replaced the rear rack with an aluminium one.

So, it took quite a lot more than I expected to do the conversion, but I managed to make an almost perfect commuter bike, and she served me faithfully for six years before I started to get problems like leaking gaskets, sticking brakes, etc, and it was time to replace her.

Supertrapp Exhaust. Noisy as standard and not that powerful.

Supertrapp Exhaust. Noisy as standard and not that powerful.

Supertrapp centre hole and missing chain guard

Supertrapp centre hole and missing chain guard

20-yr old Honda XLR250R Supermoto

19-yr old Honda XLR250R Supermoto before side panel airbox mod.

20-yr old after rolling in the dirt.

20-yr old after rolling in the dirt.