There is a thread here on RCU called gas-glow.
We are using 1 part 10/10 glow fuel and 2 parts gas.

The engines runs smoother and gain RPM, especially converted chainsaw motors.
We are using Walbro carbs.

I can't say it will make your 40cc act like a 70cc but more is better.
At this point you don't have much to loose.

Just a thought