Methanol and Walbro membranes are not the best friends. The diaphragms harden, and carb performance goes down the drain.
I have tried running glow engines with a walbro carb, but found the throttle response on glow fuel very lacking.
Some people have had very good results by changing the Walbro carb to a glow carb.
Like Dar said in his post, use low nitro fuel. MVVS engines of that time were designed for zero nitro operation. I would suggest to use 2% max. If you want to run more nitro, the heads need to be shimmed to lower the compression ratio.