What's the deal? Are the pistons 10.5:1 or 12.5:1? It isn't clear. The problem is that differnet market; different year; TR1 variants had (at least) two possible combustion chamber volumes. Early Northern European models held 55cc and had a 9.1:1 compression ratio. Later and/or Southern market XV1000s held 67.1cc and had an 8.3:1 CR. I get inconsistent feedback from my customers; a lot of these bikes were diverted from their intended markets to ones that they were not intended for.

So, two caveats: to know for sure, you must measure the volume of YOUR combustion chambers. Ten and a half is plenty. However - there are a few of my kits running reliably in early model Scandinavian market bikes. I'm told that the starters groan, but the bikes are rockets, easily outpacing Ducatis (and some four cylinders) of the same era. Cam kits help.