Project FJ Racer, How it was built

The idea was to build a budget track bike using the FJ as the basis, I had a budget for £1000 to complete though I later found this to be a bit very optimistic. The donor bike would need to be stripped down to minimal weight and maximum power without loss of reliability and handle like a modern superbike!.
First was the bike. I wanted a FJ1100 as this was once the sportiest and lightest of all the FJ range so when one came up for £200 the project was off the ground. For £200 you don’t get a lot, it had been stood in a friend’s garage for over four years so it was sold as a non runner. The cosmetics were in average shape, but complete, so once I got the engine running by replacing the carbs (they had blocked up with old fuel and were impossible to clean, so beware don’t leave fuel in the carbs for any long length of time) it was onto the next stage.
Another friend (Gordon) had a FJ1200 3CV with over 90,000 miles on it, but during his ownership, he had heavily modified it with Wiesco pistons, Exup wheels, flat slide carbs and Dyna coils etc… After an exchange of £800 I acquired his heap!
The suspension, disc’s and cosmetics were in a right state, so before stripping to find the serviceable parts I threw it on a Dyno. Whilst It produced 115bhp at the back wheel the power curve was very poor and it filled the workshop with masses of oil fumes.
A standard FJ motor kicks out 106bhp so this motor was in a sick state considering all the performance bits. When I did a compression check I found that No2 cylinder was down 40psi, so an engine strip was in order. Another added problem was a slight oil leak on the crankcases, which I later found out it had been welded to repair a crack.

engine open

Engine stripped for rebulid

carbs and filters copy


Upon stripping the engine I found three pistons with broken rings, one of which had a chunk missing and had caused damaged to the bore. The valves were pitted to the point that No 2 cylinders exhaust valves were replaced with new at a cost of £25 each. Using this head, due to it being gas flowed, I lapped all the valves in to get a good seal and fitted new valve seals.
I managed to purchase a replacement piston from the Wiesco importers plus a set of four piston rings, the only problem was they no longer manufactured the exact same pistons, so I was sent the closest they had, which I then found weighed 15 grams heavier, so a lot of machining was required to match all pistons.
Because the pistons were standard size (1188cc, though with slightly higher compression) I fitted them in a second hand set of newly honed out barrels.
Before the engine was re-assembled, I had the idea of fitting a XJR gearbox unit because this has a longer output shaft (gearbox sprocket shaft). This would allow the chain to clear the large 180/55zr17 tyre that I had planned to fit on the Exup rear wheel, as normally you can only fit a 160 or a 170 at a push.
Due to the XJR gearbox, I needed to fit a XJR gearbox casing, as this gives clearance to the sprocket and the longer output shaft.
I assemble it all together using the bottom end and crankcases from the FJ1100 motor due to the 3CV oil leaking crankcases.

Engine refitted in frame. Carb's with S&B filter plus Dynojet kit.

Piston before and after cleaning

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