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first potato gun and need help

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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first potato gun and need help

Unread postAuthor: gvfc2 » Wed Oct 26, 2011 3:46 pm

im trying to make a potato gun with a spark plug from a car peizo electric lighter and metal container. ive tried it in pvc but the park plug will not ignite hair spray. i get a good spark but still no ignition. will it only work when the flammable gasses are compressed?
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 26, 2011 3:50 pm

A car piezo electric lighter?

I thought all car lighters were of the "hot wire" type...
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Unread postAuthor: gvfc2 » Wed Oct 26, 2011 3:52 pm

sorry its kinda worded wrong there its a cars spark plug and a peizo electronic igniter
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 26, 2011 4:02 pm

Most likely problem: too much hairspray

Other possible issue: too small a spark gap - you should aim for about 1/4" and an automotive spark plug usually has a much, much smaller gap.
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Unread postAuthor: Labtecpower » Wed Oct 26, 2011 4:19 pm

Thus; maybe make the gap larger.

I think that if you meter your fuel a lot of problems will be solved too :)
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Unread postAuthor: jimmy101 » Wed Oct 26, 2011 4:47 pm

99% chance there is to much fuel
0.99% chance there is to little fuel
0.01% chance that the spark is to small
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Unread postAuthor: mattyzip77 » Wed Oct 26, 2011 4:50 pm

too much fuel, or too little fuel, also what kind of hair spray are you using?? It has to be aerosol type. Usually, a good 3 second blast should do the trick. good luck and welcome!!
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Unread postAuthor: Fexo180 » Thu Oct 27, 2011 12:42 am

Best method i have found to be pretty much fail safe is to use the humble spark igniter for a gas BBQ or gas oven...
*run the 2 wires down to 2x 5mmx 25mm bolts with nuts and washers.. o-rings aswell if you are anal about leakage..

*drill the small holes in the sides of combustion tube at say 10 and 2 o'clock....insert bolts, nuts, washers, o-rings, do them up tight preferably in a double wall..

*on the insides run 2 short lengths of copper wire... insulated.. un-insulated.. whatever you have... i found thicker to be better but it needs some flex.....

*breech load via a back screw cap.. used to shoot a lot of tennis balls.... *adjust the internal wires so they are in the MIDDLE of the chamber, give it a dry fire to test the spark.. you should get atleast a 3/4 to an inch arc.


the reason i adjust the wires to the center of the combustion tube is to get a better burn.. trust me it works way better this way.

Fuel... i found least to be best... 'Start Ya Bastard' is the shiznay but BBQ LPG is better just squirt a bit in...screw on cap.. point and fire.

hope this helps some.
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Unread postAuthor: gvfc2 » Thu Oct 27, 2011 12:54 am

I wanted to use a spark plug as i have a couple on hand. i gaped them to as wide as they go and still make spark them closed them alittle to insure spark everytime. i use aquenet hair spray. i also used ether with a very short burst and that didnt ignite. so im still at a lose. but its late here so i have to stop work on this for the day. i might just go back to working on my dirtbike. but i will update with well updates from time to time
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 27, 2011 12:56 am

http://www.spudfiles.com/forums/how-to- ... 22301.html

fuel metering does not have to be complex and should solve your problems.
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Unread postAuthor: Dubz » Thu Oct 27, 2011 1:06 am

Try using a small spark plug off a RC engine and use a lighter refill valve epoxy in a small hole on the chamber so you can just use lighter aerosol refill gas, just one or two quick burst with the gas, you won't loose any gas that way
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Unread postAuthor: Dubz » Thu Oct 27, 2011 1:08 am

Try using a small spark plug off a RC engine and use a lighter refill valve epoxy in a small hole on the chamber so you can just use lighter aerosol refill gas, just one or two quick burst with the gas, you won't loose any gas that way
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Unread postAuthor: pneumaticcannons » Thu Oct 27, 2011 5:30 am

I've had a LOT of spark gap problems. usually the issue was me having too small of a spark gap. Might be too much fuel though.
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Unread postAuthor: mattyzip77 » Thu Oct 27, 2011 12:57 pm

Try spraying your fuel for a full 3 seconds without getting fuel on the electrodes. Get rid of the spark plug as well, you do not need it!!!
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