whats the timing like? you shouldn't be getting ignition on the other side of the valved at all, the car should at the very least splutter or something with the screws tuned wrong.
though in saying that, i did too ONCE get a flame poke out the top of my 32/36. not sure why (ive fine tuned the timing since them so maybe that), but its the reason i dont run foam filters, fire hazard at best...
edit, ive fixed a lot of motorbike engines by starting the engine with engine start and then revving it for a bit and just running fuel through the whole lot, i can get a nice base tune on it and it starts quite easily afterwards for fine tuning. just don't start the engine on engine start all the time cause it'll only cause damage