RE: Aquacraft Super-Vee 27 Nitro.
If there is sufficient fuel, a hot glow, and decent compression than the engine will start. There's no tricks here.
Exhaust pressure or not, the engine should still start after priming it.
Do you visually see a nice bright orange glow from the plug when it's out? Have you replaced the plug just to confirm it can not be the plug? Does the engine fire at all when turning it over?
Ryan