the flywheel has not been off and runs true and there is no play in the bearings in any direction i am therefore convinced its the piston weight judging by the way it literally jumps up and down and it's the only thing i changed from the original set up which ran ok at 1000 rpm 

yes the dk runs a lower compression , my other 2 'd' run fine after overhauls ,but there's all ways one that fights back ! . i will investigate and report back

hi yes i  totally agree i guess that's why lister didn't include the piston in the dk conversion kit , i got the engine from the original owner who had it new in 1949 and fitted the kit , i presume listers balanced the engines according to spec ,   

 i have just over hauled a dk which  had the factory conversion fitted and still had 2 head gaskets , it ran fine but needed a good decoke  , i fitted a flat top piston just to make it correct and it runs fine but it shakes , crank / flywheel run true , timing spot on it is a 2hp 1000 rpm engine with the smaller flywheel , its ok at 750/800 rpm so might just change the gov springs , has anyone got any ideas ? my other 2 ''d's '' run dead smooth but are both 1.5hp 750 rpm units

hi all has anyone found a good product like jb weld etc in the uk for fixing pin holes in a fuel tank , the tank is totally dry having sat for years , any thoughts appreciated