Second potato gun, poor results

[Stampede10343]

Alright so i made a few simple spray and pray guns and have been browsing this site for answers but i still have a few questions..

My first gun is a 3" T and a 2 1/2 ft 2" PVC barrel and shoots about 100 yards with hairspray as fuel. I wanted to make a more powerful gun, so i decided to use a 4" x 20" combustion chamber and a 2" x 48" barrel. My first test shot the potato went about 15 yards, with a 2" spray, it felt like a really slow ignition so i tried again with not much luck. I came back on here and read about mixing the gas so i put a plastic golf ball in the chamber and mixed it up and got the potato to go about 100 yards. So i was wondering how can i make this any better since 100 yards isnt that impressive for a gun of this size..

Thanks, Stampede

[clemsonguy1125]

A couple things you can do
1.Add a fan, this will help with your fuel mixing problems even more
2.Fuel mixture, theres a good chance you fuel mixture is not the best, experiment with different amounts or hairspray to find the best mixture
3.Even better than playing with the hairspray mixture is metering propane, you can make a fairly simple propane meter, browse through the combustion showcase for good examples of advanced combustions, starmans triple thunder are great examples. To find the right meter pressure you can use burntlatkes calculator or how to on calculating meter pressures
Good Luck,

[Stampede10343]

Thanks, i'll try using a fan and testing different mixtures and see where that goes.

[jackssmirkingrevenge]

A simple syringe meter is an easy way to get the correct amount of fuel into the chamber, use one and you'll be impressed with the consistency and power increase.

[metalmeltr]

shorten your combustion chamber, there is a calculator on burnt lakes site that can tell you the ideal chamber size for certain size barrel, there is also one to calculate meter pipe size if you decide to do metered propene, after i set mine up for propane i never went back to spray and pray

[Stampede10343]

Well theres good news and bad news.. i got a fan in the combustion chamber, good news is that it is more consistent, bad news is that it seems to consistent.. No matter if i do 2" or 8" of right guard it still goes right around 100 yards.. what now?

[Heimo]

what now?

now you add metered propane to the setup