My 914 had been in storage for 10 years before I had the urge to take off the cover and get the engine runing, but when it is started it constantly puts out a greyish smoke. Before I put it in storage I put new valves and valve guides in it, could it just be that the carbs are not tuned properly.

yes.
did you change the oil before you fired it up? did it have any oil in it while it was stored?
did you drain the gas-tank prior to startup? did you replace the fuel-filter?

if the motor still had oil in it and you drained it, was there white sludge in the oil?

Andy