The engine will be a little harder to start on the no nitro mix and wont idle as nice as even a low nitro fuel like 5% without changes to the combustion chamber shape and a hot glow plug. You could always prime the engine prior to starting with a few drops on nitro based fuel through the venturi of the carb, and speed the idle up a little more than usual. If you run a hot plug you shouldnt need to keep a glow driver on it when running. Hotter plugs are more fragile though, thinner element wire.

(For the record, I used a 15% BeNol / 85% methanol mix to after-run my high nitro marine engines to burn out any residual nitromethane prior to oiling. They can be harder to start on this mix, but they are set up for lots of nitro and run cold plugs.)

If the carb was tuned for different fuel previously, it will more than likely be out of tune for the new mix. Particularly if nitro was involved.