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trouble with firing

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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trouble with firing

Unread postAuthor: gotbass7 » Sat Jun 02, 2007 2:50 pm

Recently, i made my second, more traditional, spudgun. the problem is i only got it to shoot once and it didnt shoot very good, but thats because the potato didnt have a tight enough seal.
well i tried to shoot it again and it didnt work at all. i tried several times, with a lot of fuel, barely any fuel, and everywhere inbetween. nothing. i checked the ignition. it worked. i think it might have something to do with the spark gap. i am using the ignitor from a long nosed lighter. but anyways the spark gap is very small. it has a spark, but a very tiny one. any help/suggestions would be greatly appreciated. im using axe.
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Unread postAuthor: lukemc » Sat Jun 02, 2007 2:57 pm

i dont care what you say if you have a spark than you dont have the right amount of fuel. an electrick spark is hotter than the surface of the sun so if there is a spark in that chamber with good fuel than is will work. how bigs your chamber i might be able to give you an estimate time for spraying
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Unread postAuthor: Pete Zaria » Sat Jun 02, 2007 3:01 pm

A spark gap of 1/4" or less should work fine for igniting atmospheric-pressure mixes.

The obvious potential problems I see are

A) fuel/air ratio/mixture is off (try less... or a different fuel)
B) fuel is not mixing with air well enough (chamber fan)
C) temperature/humidity/etc... conditions are creating problems.

Try less fuel. Try using propane from a torch (unmetered, starting with a little bit and working up) or engine starter/carb cleaner.

Try installing a chamber fan (80mm comp fans fit great in 4" pipe, 40mm fans will fit in 2"). A 9v battery and switch will run them. A 9v and two AA's in series make 12v and run it faster....

Make sure you're airing out the chamber between shots well enough, also.

Peace,
Pete Zaria.
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Unread postAuthor: gotbass7 » Sat Jun 02, 2007 5:21 pm

ok. ill just let all the fuel in it now just kinda go out by keeping the cannons ends open. the chambers not much bigger then the barrel. i think its the smallest difference adapter for abs piping
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