I don't know how many out here are familiar with the Rambler 45, but, it has retracts. A lot of planes with retracts have this same problem, as do some scale models. The problem stems from the main gear being too close to the CG and running the plane a little nose heavy, will cause it to nose over, simply because of the fulcurm point. Try to move your balance back to the CENTER of the recommended range and see if that helps, I think you'll be very surprised.

Ken