Hi all , recently bought a beta techno 1997 , the bike seems fine mechanically and rides fine up until I've been out on it for an hour or 2 , the bike breaks down and will not start again , then I replace the plug and it will start and run fine again but I know this isn't normal , this has happend on 3 consecutive occasions since I bought the bike I replace the plug and it will break down after an hour or 2 , wondering if anyone has had a similar problem or if anyone has any idea what could be the problem ? Cheers