Originally Posted by tooter
OK thanks was hopeing for something a bit more constructive but thanks anyway
Actually that probably is constructive. No offence intended but without some experience in the area you are potentially more likely to do harm than good (as Nos4r2 has already suggested) and if you had that experience you probably wouldn't be asking here where to start.
Essentially any petrol engine needs the following to run:
fuel and air in the right mix
all at the right time! The engine has been sitting for 20 yrs, if it was "put away" in perfect running order, winterised before being put away and stored somewhere nice then its feasible to put fresh fuel/oil in it turn it over and off she goes, but if its turned over - even slowly - without oil getting to the cylinders you can cause significant damage, all the more likely with an engine thats potentially been stored badly. Depending how it was stored the carbs may be blocked. If no fuel is getting in, then on an old pre-mix 2 stroke no oil is getting in either.
Assuming the stiffness turning over is not a trivial problem with the pull chord mechanism then its a really bad sign. If the head needs to come off (even to investigate) that is not a "beginners" job especially on an old engine with potentially seized bolts etc.
If its an easy fix £50 ish for an hour of a marine engineer's time and your engine is running. If its goosed then you find out before you've wasted a whole load of money on parts and a several hours of grief working it out for yourself. You'd also be able to sell it for spares/repair with a description of whats wrong which will get you more money than "stiff to turn over".