Have problem with flame back in venturi tube - Desa International TT15G Heater

Orange flame is not enough air in the gas air mix. You have a spider nest living in the venturi tube and nozzle. Weber sell a special brush. The venturi tube is between the gas control knob and jet and the burner.

Strip it down behind the knob and the venturi tube. You have spiders nests back there and the flame is pooling there instead of firing down the venturi tube to the burner. The venturi mixes air with the gas.

Possible blockage in Venturi to burner

If your grill is older and has seen several seasons check for obstructions elsewhere the venturi is only one place for problems, check for hose kinks loose connections. If this is in a cold weather area, it maybe just low pressure. Also look for collected/ponded water in the burner tubes, especially if the flames are yellow.

If your propane tank is not just about to run empty, then you can probably thank little spiders.
When a gas burning appliance sits idle for a week or more outdoors, spiders like to build nests in the venturi tubes (that's the tube with the holes in it where the combustion air gets sucked in). This changes the way the combustion air mixes with the gas and causes the gas to not burn completely. The incomplete combustion is not very hot, and so the flame appears yellow. This is not efficient. It wastes gas, is too cool for grilling steak and creates soot residues. This is very common on gas grills (bottled propane or piped natural gas). It also happens to pool heaters.
Fortunately, the fix is easy, and you usually don't need to take anything apart. Get a piece of stiff nylon string from a weed-wacker, about 12 inches long. With the burner cool, push the string into any hole in the venturi tube and spin it by rolling it between your fingers. The spider nests are sticky (made from the same stuff as spider webs) and they usually adhere to the nylon string.
Not sure what the venture tube is? It's going to be between the valve and the burner. The valve shoots a stream of gas into the venture tube through a pinhole nozzle called an "orifice". You can do a Google image search for BURNER VENTURI TUBE to see lots of different types. Every gas burning appliance uses some form of venturi tube.

blocked burner , or split burner , gas lighting back to injectors wrong air mix, leak on control panel ,

Can you see the smoke coming from the tip of the flame itself? Did you not have this problem before you replaced the burners? If yes to both, then the problem is with the venturi tube of the burner not providing enough air. The venturi tube is the part of the tube where the gas jet from the valve first enters it. There are some holes that control the air/gas mix by their configuration and size. Perhaps you have the wrong model replacement burner. The orifice (very small hole) out of which the gas shoots into the venturi, and the venturi tube itself are both designed slightly differently for use with Propane (bottled) or Natural (piped) gas. Perhaps your new burner has an adjustable venturi to allow more air. If so, remove the rocks so that you can see the flame and adjust by trial and error.

check for a blockage in the lines---sometimes spiders will build a cocoon in the tubes.

Barbecue Repair Parts Don't let spiders crawl into your venturis, yearly maintenance part are available. If you notice that your Barbecue is getting hard to light or that the flame isn't as strong as it should be, take the time to check and clean the VENTURIS. In some areas of the country, spiders or small inserts have been known to create "flashback" problems. The spiders spin webs, build nests, and lay eggs in the BARBECUE VENTURI TUBE (s)obstructing the flow of gas to the BURNER. The backed-up gas can ignite in the venturis behind the control panel. This is known as a flashback, and it can damage your Barbecue and even cause injury. To prevent flashbacks and ensure good performance the BARBECUE BURNER and VENTURI assembly should be removed from the grill and cleaned before use whenever the BARBECUE has been idle for an extended period of time.

Also, when you lite the BBQ, make sure that you turn the gas on at the tank, wait a couple of minutes and then turn the knob on and light the burner. This is to make sure that the pressure is regulated and sufficient prior to lighting.

Hope this helps!

Barbecue Repair Parts Don't let spiders crawl into your venturis, yearly maintenance part are available. If you notice that your Barbecue is getting hard to light or that the flame isn't as strong as it should be, take the time to check and clean the VENTURIS. In some areas of the country, spiders or small inserts have been known to create "flashback" problems. The spiders spin webs, build nests, and lay eggs in the BARBECUE VENTURI TUBE (s)obstructing the flow of gas to the BURNER. The backed-up gas can ignite in the venturis behind the control panel. This is known as a flashback, and it can damage your Barbecue and even cause injury. To prevent flashbacks and ensure good performance the BARBECUE BURNER and VENTURI assembly should be removed from the grill and cleaned before use whenever the BARBECUE has been idle for an extended period of time.

Hope this helps!