Spud Gun Not Reliable?

[The Master Weaponist]

Hey Guys,
I just made a spud gun from a coke bottle and a pen's tube and used a piezo ignition. I use regular axe but the fuel-air ratio is extremely picky. Before I could get it to fire 50% times but as I practiced it is now 80%. Like I have seen 1 short spray enough but after a misfire I have to shake it around for the fuel to air ratio to be good. Is there any thing I can add or do with the fuelling system for better reliability?
Thanks

[jackssmirkingrevenge]

[youtube][/youtube]

[jimmy101]

Your chamber is about a gazillion times bigger than that barrel needs. Besides the technique Jack's video shows you can also use a butane lighter and a short length of wire insulation. Even without a syringe the counting method will be much more reproducible than with a spray like Axe. A chamber your size will take several seconds to fuel with a butane lighter and you can count several seconds in your head a lot more accurately than you can get a proper squirt out of a spray can.
Like this
Long neck lighters come with a convenient hose already attached