Never clean the INSIDE of the engine, you don't ever need to clean the inside of the engine!!
If your airfilter is present and you keep the head clean before you take out the glowplug, the inside of the engine will never get dirty. (If dirt has got in, your engine is history. No spray can save you.)
For use *outside* the engine... 1:1 carby & brakecleaners contain thinners etc, some of it can melt plastics.
Best to buy an RC "Motor Spray" or some brands also sell a "Nitro Wash" spray can.
There should NOT be any residual fuel in your engine... if you look after it right.
When I finish running my car, I'll always
1) run it until it stops due to out of fuel
2) make sure the tank is really empty
3) put your glow warmer onto the plug
4) crank the engine for 30 secs
Even with the tank dry, usually there's enough fuel in your engine remaining to make it jump back to life for a few seconds. Doing this clears the engine & fuel lines of ALL fuel.
5) take out the glowplug & airfilter, put a few drops of After-Run oil into the chamber and carb. Crank the engine over a bit to distribute the oil.
You can buy special RC After-Run oil... or just use any light machine oil, some ppl even use ATF (Auto Trans Fluid). The oil just stops anything in the engine rusting - burning methanol creates water.
lastly - special trick of mine...
6) Leave the fuel tank lid OPEN! Yeah, get a wooden dowel or anything clean to jam the lid ajar, don't store it closed. When the remaining fuel evaporates it leaves behind water; give the water a chance to evaporate too - water don't burn.
Is your car hard to start 1st time now??
With your car prepped like that... it fire up sweet next time like you will not imaging.