Some details perhaps? Wing span? Wing area? There is no specific weight beyond which the motor ceases to work.

In general? You'll want a model not much over 2-2.5lbs based on 350-400 in/sq wing. Lighter is always better. You can save significant amounts of weight by using mini-servos & rx in a plane this size, well as replacing NiCd batteries with much lighter NiMh cells.

If you look after the ounces....the pounds will take care of themselves.

'Race