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gun 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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gun problems

Unread postAuthor: evallia » Mon Aug 23, 2010 11:09 pm

Alright my big gun ain't working right now its 5' 2" barrel and 2' 4 " chamber and it only shoots a potato another wo20 yards I'm using rightguard for fuel any suggestions?
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Unread postAuthor: clemsonguy1125 » Mon Aug 23, 2010 11:26 pm

Was the potato a good fit, how much fuel did you spray in, I'm assuming it doesn't have a fan. Air out the chamber and try for a 2 second burst of fuel.
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Unread postAuthor: hi » Tue Aug 24, 2010 12:09 am

Just got to get the fuel mixture right. A lot of people think more is better, and that certainly isn't true in the case of spud guns.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: Ragnarok » Tue Aug 24, 2010 10:24 am

Ninety-nine times out of a hundred, when someone comes to us with this problem, the problem is exactly as the two people above have said.

There is an optimum fuel mix - too little or too much fuel will limit power. And given the tendency to think "more fuel = more power", usually the problem is the latter. Try less fuel and see if it works better.

Also, do make sure you let the burnt gases vent out of the chamber between shots. You need fresh air in the chamber. I'm sure you know the fire triangle with Fuel, Heat and Oxygen? The fuel is your Right Guard, the heat comes from the spark/whatever ignition you're using, and the oxygen has to come from fresh air. If you haven't got enough of any one of these things, then it just won't work.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: SpudBlaster15 » Tue Aug 24, 2010 1:19 pm

Considering the length and subsequent volume of the chamber, I don't believe the issue is related to over fueling. Most likely, it's improper fuel distribution and mixing that's causing the problem.

Your chamber is far too large to be used without a system to aid in fuel mixing. Adding a chamber fan, or simply cutting the chamber down to half its length would significantly boost performance.
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Unread postAuthor: jimmy101 » Wed Aug 25, 2010 6:49 pm

Easy enough to definitively tell the difference between a fuel ratio problem and a fueling mixing problem.

Air out the chamber.
Load a spud (or whatever).
Fuel as you normally do.
Let the gun sit for a half hour or so. Invert it a couple times during the wait.
Fire.

If the performance goes way up then you definitely have a mixing problem.
If the performance is about the same then your fuel mixture is off (probably too rich).
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Unread postAuthor: bighead33 » Wed Aug 25, 2010 11:43 pm

maybe your using the wrong right guard. be sure your propellant is flammable.
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