Between 1987-1990 Yamaha Motor Europe initiated a race class for the TZR250. A kit was offered to the riders which consisted of some specially made parts and parts that came straight from the TZ250 production racer.
Nearly all these machines ended on the scrap heap, and/or the frames were used for "Sound of Singles" categeries and the likes later on. I had a nearly new TZR250 with few miles and "found" a complete kit somewhere....... Here is the description of the modifications to the standard bike if you want to build something like that yourself.
The racing crankshaft has 49V (TZ250L) connecting rods and bearings, the taper is also different for the racing CDI magneto.
The gearbox is close-ratio and replaces the standard cluster, the clutch is standard but has heavier springs (90501-23700)
These are standard cylinders/pistons. For the racemodel the exhaustports are widened from 39>41 mm and the upper edge is radiused from 24,9>23,5 mm from the top of the cylinder. On the exhaustpipe end the opening is enlarged from 32>37 mm.
The thin racing cylinder head gasket is superior in quality/strength.
Cylinderheadmodification consists out of re-shaping the combustion chamber with a 45 degrees angle formed by the cylinder head mating surface and the tangent line touching the spherical surface having a radius of 19 mm. The result is a cylinder head volume of 11.4 cubic centimeters.
Modern Yamaha TZ250 sparkplugcaps are being used.
The carburetors are modified. The small steel ball that blocks the airpassage is removed from the backside (left is the pilot air jet, next the hole where the ball was pressed-in) These carburetors have a backplate that can be taken away, very easy! After that the first part of this hole should be re-drilled in steps up to 2,5 mm. Next the normal hose outlet should be blocked in some way. I simply glued a ball into the hose and cut it off. I use a 260# mainjet, 5EJ48 2nd step jet needle, P-8 needle jet set and a 27,5 pilot jet.
The fuel cock of the TZR250 is very unhandy. I replaced it with a standard 4DP (TZ250) fuelcock, mounted on an aluminium block, in which a groove was machined for the o-ring.
The ignition is very special CDI type with a different advance curve, similar to the TZ250 Production racer. It was supplied with a special bracket for easy fitting.
The instrument panel consists out of a foam panel on an aluminium stay, which bolts on the old fiting lugs for the standard TZR cowling. The tachometer is the racing type, as temperature gauge I used a cheap car-type unit.
In the kit where nicely made rearset footrest and pedals, here the l.h. assembly.
On the r.h. side there was also an aluminium extension plate for more rearward mounting of the rear brake cylinder, as can be seen here.
The racer set-up requires a battery pack to supply the YPVS system with current, but as these packs are fragile and do not last long I decided to use a normal battery. Therefore I kept the battery carrier and black plastic rear mudguard. The batteryholder was modified a little (I use a WR450 dry battery) and an old headlamp light switch was attached to a small stay made from angle aluminium.
Here is a detailed view from the inside to the battery and its new bracket.