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1st combutstion cannon firing problems

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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1st combutstion cannon firing problems

Unread postAuthor: redalpha11 » Mon Jul 28, 2008 10:47 pm

so this is my first cannon ever. i am following guidelines from http://www.mshamash.com/spud/spudgun1.html . i have been researching spud guns for the past month. so i finally decided to build one. but i have one problem it wont fire it does spark nicely. i have tried various fuels with different fuel to air ratio. it fires every now and then but i could use some advices here are the pictures. :?

heres the starter ,chamber
<a href="http://img197.imagevenue.com/img.php?image=01874_DSC02216_122_503lo.JPG"><img src="http://img197.imagevenue.com/loc503/th_01874_DSC02216_122_503lo.JPG" border="0"></a>

ignitor
<a href="http://img13.imagevenue.com/img.php?image=03075_DSC02233_122_625lo.JPG"><img src="http://img13.imagevenue.com/loc625/th_03075_DSC02233_122_625lo.JPG" border="0"></a>


fullcannon
<a href="http://img212.imagevenue.com/img.php?image=02665_DSC02230_122_469lo.JPG"><img src="http://img212.imagevenue.com/loc469/th_02665_DSC02230_122_469lo.JPG" border="0"></a>
so how can i make it propel a potato thourhg the air
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Unread postAuthor: frankrede » Mon Jul 28, 2008 11:10 pm

Try using more fuel?try using less?
Make sure you vent after attempt
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Unread postAuthor: brogdenlaxmiddie » Mon Jul 28, 2008 11:40 pm

What I did when I started my first combustion spray and pray, I put in 1 second of continious spray and then tried that. Then two seconds, then three and so on. I found about 3 seconds is the best for me. But like Frank said, make sure you air it out well.
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Unread postAuthor: nosebleedXD » Mon Jul 28, 2008 11:55 pm

happens to me, sray for 1second then blow into it. sometimes it needs some ciculation. try waiting 2-4 seconds before closing cap
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Unread postAuthor: starman » Tue Jul 29, 2008 12:45 am

Your spark gap is little wide...narrow it down to at least half what you have now. Also, bringing your wire back outside isn't necessary...find a way to connect it to the screw from the inside there. Or better yet, just connect a stiff wire to the ground lug and build up a gap by pointing it at the center spark terminal...about 1/4" away.
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Unread postAuthor: ralphd » Tue Jul 29, 2008 7:00 am

Try using Aqua Net. That was the key for me. I tried everything. On your next one use propane or mapp. Less mess more better. Finally, switch to tennis balls...lots more fun and no mess.
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Unread postAuthor: redalpha11 » Tue Jul 29, 2008 9:29 am

i am just a little worried about the chamber it is mad0e of Cresline coextruded cellular pvc but the dude at ace said it would be strong enough. so i would just like you guys opinions about it. also thankyou very much about the fuel.
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Unread postAuthor: nosebleedXD » Tue Jul 29, 2008 10:40 am

i thought your gun wasn't able to fire properly at times

your pipes and stuff are fine, just make sure you've glued all your parts on properly

and your sparker, its may be too far apart from screw and is also crooked from my perspective from your picture
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Unread postAuthor: Mr.Sandman » Tue Jul 29, 2008 11:04 am

maybe get a propane meter? they are always right with the amount of fuel.(as long as you air out the chamber)
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Unread postAuthor: redalpha11 » Sat Aug 02, 2008 8:40 pm

well my cannon will fire betaine a a lighter but wont fire any thing else icave tried aqua net and raid .is there any other aerosol out there i can use with a really good rate of succsess.
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Unread postAuthor: McFear » Sun Aug 03, 2008 2:49 am

are you venting gas after each shot. stupid question i know, but it does happen. also as said above, make the spark gap much shorter. get it as close as you can without having it touch would be best.
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Unread postAuthor: ralphd » Sun Aug 03, 2008 5:45 am

If you're using those fuels and still having ignition problems and you say that you have consistent spark then my guess is air. I had the same problem when I first made mine and my wife rode my ass about the money I spent. Then I installed a simple thing which made her eat her words, a combustion chamber fan. If you still insist on having a spray-n-pray though then don't make it a part of the launcher. Make it detachable, something to use between shots.
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Unread postAuthor: frankrede » Sun Aug 03, 2008 11:26 am

That igniter is unsafe!
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Unread postAuthor: Coodude26 » Sun Aug 03, 2008 11:40 am

Frank you mind explaining?

And IIRC isn't cell core going to kill you? Even if it is stronger isn't it still less strong than regular PVC?
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Unread postAuthor: Mr.Sandman » Sun Aug 03, 2008 11:46 am

i spray for about 3 secs then i blow one big huff in the chamber kinda like a cough
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