How to make a venturi setup?

[apples]

Okay I have my gas pit going. It is making a fair bit of black soot as it burns. Looks like I will need to make an air mixer or venture to suck air in.

Right now all I have is a few fittings that are connected so that it goes from the 5/8" UNF gas thread to the BSP water pipe threads.

How would I make a venturi for it? I don't think that I can just drill a few holes in the fittings?
I think I need to constrict the gas flow into a high speed jet then somewhere around there drill a hole?

Any ideas guys?

Here is a pic of it going.

[MLMartin]

Venturis burners are often used in vary low pressure applications. The water sitting in the pot will add a far bit of pressure to any burner. You may need to add some type of pressurized air to the system instead of a venturi set up.

[sfDuck]

You might want to look at black iron pipe fittings, a 3 or 4 inch reducer to 1/2 inch then add a 1/2 inch nipple thats 6 to 12 inches long. A welded strip across the 4 in end of the reducer with a suitable hole in the centre to hold whatever size oriface spud ( Brass)you choose. The gas under pressure goes through the oriface and out the half in tube. As it does this it sucks combustion air into the mixure and you have your venturi. Slight adjustments will be needed to get the flame and amount of heat required. The gas line going to the venturi must have a possitive shut off before the venturi. I used a 1`/2 in ball valve rated for gas, its quick to shut off. I got my orifaces from old gas furnaces. Check the rating plate on the furnace. If the furnace is an 80 thousand btu's , count the number of burners and divid that into the rating and thats how much your home made burner will produce. Adjust the oriface hole size accordingly by redrilling. Using thumb drill sizes. If you drill too big a hole, braze it over and redrill; keeping the same inside and out shape as you started with.