175 BSA Bantam of indeterminate age that I had in 1975. It was my road bike on which I hoped to pass my test.
My other bike was an Ossa 250 MAR which I bought new and cost me nearly £600 in the days when a Jap 250 road bike would cost about £350. The Ossa was road registered and had a set of lights that worked off the magneto (yes, magneto) but since I also did trials on it the lights had usually been smeared over the nearest hillside during the weekend, or the handlebars would be bent to buggery after dropping it or flipping it. Not the sort of bike you'd impress an examiner with if it had bits dropping off and bent bits after a trial.
Hence the Bantam. A dirt cheap road bike that would be good enough to do my test on. Never managed to get the pre-mix right and it would start to nip up if it didn't have loads of oil (seem to remember 16:1) and this was in the days before synthetic so I would be going down the road with 2 stroke smoke belching out of the exhaust - until the exhaust spat it's baffles out which happened every 10-15 miles - once in front of a police car. The electrics on it were a nightmare as well and the brake light (which was the main reason I wanted the bike so the examiner could see me braking properly) would play up - in fact the whole rear light was hit and miss.
On the morning of the test, it wouldn't start, so I did the test on the Ossa after all - needless to say the Ossa's lights weren't working so I did my whole test on hand signals. This was in the days of the examiner just watching you ride around the block and nipping through alleyways to keep you in sight. The 'low speed control' test was fun on a trials bike though all you had to do was ride alongside the examiner at walking pace, and with the Ossa in first gear he had to keep stopping for me to catch up