Thought I'd let you now, it's now working a treat!
I've shortened the gap slightly, it's now around 4mm, but I still need to short the contacts after it's fired.
The biggest difference came from airing the combustion chamber each time. I'm using a sink grease trap as part of the combustion chamber ...

Sorry, you're right, I' meant 6 mm! I'll give it another go with 3mm and see where I get to.
Cheers
P

Thanks for all the pointers, there's no shock when I short the points, and I'm using wood screws with around a 60mm gap, it was sparking happily yesterday (and flinging hotdogs happily too, when it wasn't blowing apart!)
I'm wondering if it's something as annoying as humidity, it's felt a bit too ...

Hi,

I'm using Lynx (Axe in the rest of the world) deodorant, I'm pretty sure it's not down to dirty contacts, as even with no propelant I'll get 2 or 3 arcs and then nothing.

Cheers
P

I'm using a BBQ ignitor, that's arcing via 2 wood screws (I live in the middle of nowhere so I'm being all low-tech!)
When it fires it's great, but it seems a bit too hit and miss to me!

Hi,

I've got an issue with my combustion cannon where the ignition will spark for the first couple of goes, but then nothing....
If I then short the ignition pins with my finger, it'll spark again. As I'm still trying to figure the best fuel mixture (it's a hot dog cannon built with a grease trap ...