just got my ossa 350 gripper back together after the psiton rings yet and a thought struck me, being 1980 would it be better to run it on leaded or unleaded, will it make much if a difference either way, im not bothered about performance, just wondering how running unleaded in an engine that old will affect engine wear. oh yeah, does anyone know what sort of mix i should be running, we ran it on 25:1 but we dont know

It's a 2-stroke so you don't have to worry about engine wear on unleaded, that is only a problem for 4-strokes as it can cause wear on the valve seats with some of them. Just use a good quality, high octane brand of unleaded like optimax and it will run fine. 25:1 is way too much oil though. Modern oil like Castrol TTS which burns clean and doesn't gum up exhaust and plug should be run at 50:1 on an engine like the Ossa which has conventional steel liner. Only the modern bikes with nikasil or chrome liners use ratios like 80:1. Set your ignition timing at 2.5mm BTDC and it should run well. If the engine is is in a good state they're quite a pokey bike - at least the only decent one I ever tried was.