Hello Wahid,
In answer to your question, no I don't think the weight is the problem. With the 15 size engine on that gyro you should still be able to fly if your gyro is set up right in all other respects. For example, proper hang angle,
proper down thrust angle on the engine, sufficent lateral and pitch movement on the rotor head, incidence angle on the rotor blades and rotor blades that have a good airfoil that will lift the vehicle. If the rotors are spinning fast enough and everything else is set up per plan, it should fly. Weight is always an issue to consider but with enough power it is not your problem in this case. I think you may have a problem with the flat plate fiberglass hub. You say your having trouble with control? I've been experimenting with fiberglass hub plates for 15 size gyros. I've tried three different designs with no satisfactory results. One was .010" thick, one was .015" thick and the third was .015" with part of the sides removed to provide more flexability.
After flight testing, none worked as well as the Baxter design poly hub with the 15 degree delta. All three made control a full time problem. I've posted three photos of the failed fiberglass hubs that were not satisfactory.
I suggest you might give that poly hub another chance. I hope your Gyrostick built per plans works out for you.

Good Luck!
Joel