Hey Guys, I have an interesting problem, I hope it has happend to others so someone can explain it to me.

My small block chevy won't stop running, I know that happens sometimes to motors (detonation) but this thing is like "possesed". As for the internals of the motor I can't say. I got the SBC cheap and I was hoping it would do for a while till I build something else. At present it only has headers on it with about 3 foot of pipe. Once I start it it runs a bit rough but it still runs ( I haven't started tuning yet). Here is the fun bit
I turn off the key.....It runs
I unplug the power lead to the HEI.......It runs
I isolate the battery IT STILL RUNS.
I stick my hand over the carb and choke it to death....IT STOPS.

What is causing this?
Thanks
Andy.