Hi Jon,
The Dragonfly should have straight 40 grade oil in the engine, and according to the handbook, the gearbox should use 140 grade oil. I have always run straight 40 (as used in the earlier Mk series) in the gearbox on my 'Fly without any problems. Back in the 50's, the press were picking up on things like mechanical noise, and I think Douglas made some changes that did nothing for the performance of the bikes!
When we were forced to use the dreaded unleaded, I started using additives as there was concern about valve seat erosion. I found that the 'laced' fuel went stale much quicker, so took a chance with it unlaced and haven't had any problems. The only thing I would recommend, if you do not use the bike regularly, is to turn off the fuel and allow the engine to run until it drains the carb. That way the fuel doesn't dry out to leave a lacquer in the float bowl and jets.
Depending on your weight, the recommended tyre pressures are 22/24psi both front and rear.
Regards,
Eddie.
