Plan instructions for the ARF I am currently assembling calls for a firewall-to prop distance of 4.5 inches. The rear mounted carb of the OS FS-70 II Surpass and the engine mount makes this impossible. Moving the engine as far back as possible leaves the prop too far forward about 3/16 inches. Will this have any significant impact on how my model flies? The model is a WM Rambler 45.

Flyboy,
It is doubtful the 3/16 will make much difference to the flight envelope of the plane. What will make a difference is the weight of the engine as compared to what the plane was designed for. Check the balance carefully as the heavier engine may palce the center of gravity forward enough to make the elevator input "mushy" or require more elevator throw than called for in the plans. Good Luck! Bill

As this is a World Models ARF it is probably using the same engine mount as what was in my World Models P-51.

I mounted an OS FS-70 II inverted in this plane and had to use a dremel to remove some of the engine mount cross beam to get the engine far enough back.

Both the top and bottom cross beams had mouldings for use by the front wheel on a tricycle landing gear configuration.

I just removed this part of the bottom cross beam and the engine sits back far enough now.