WE HAVE A NUMBER OF LPG IMPERIAL IFS40 FRYERS WITH A VERY LARGE FLAME ESSESIVE FOR THE UNIT FLAMES BURNS AND EXTENDS AT THE BACK OF THE FRYER INTO THE FLUE . WE HAVE CHECKED THE CORRECT INJECTOR , CORRECT BAFFLE NUMBERS, A LP ROBERTSHAW GAS VALVE

The heat exchanger might be a result of the yellow flame but not the cause of it burning yellow. I would guess it is the amount of air being mixed with the gas. Most burners have a slotted metal air mixture ring on the front of the burner near the brass orfice, you are calling a jet. There is a locking screw to release the ring so it can turn to adjust the amount of air being mixed with the gas. If this doesn't fix the yellow flame it could be a gas pressure problem that could be the external regular in the gas line. Not sure if you are talking about the pilot flame or the burner flame or both? A tech should know how to adjust the air mixture.

It sounds like your gas line either is clogged or your heating tubes are clogged up with oil/dirt/gunk? You can blow these out with a small hand held compressor or if you have a small enough brush, you can use that to clean it. The compressor is the quickest way, but have you cleaned this unit at all? Using a fryer boil out and running the fryer will also help clean out your holes, but again, the compressor works best.

Check your manual and make sure your burner is configured for the gas that you are using. In most cases, there is an orifice that needs to be changed for using LP, or a screw setting that needs to be changed- most new appliances ship with a "city gas" configuration ( AKA NG - Natural Gas) and need to be configured for LPG (Liquified Propane Gas). The fitting(s) that need to be changed are tagged. This is due to the pressure difference between NG and LPG. Propane (LPG) runs at a higher pressure.
You state that your fryer is LPG. If you are running it on NG ("city gas") you need to consult your manual for converting it to NG. Outside of making sure that you are set up for the right gas, you should not have to make any other adjustments. For safety reasons, gas regulator pressure adjustments are for the most part no longer possible on gas appliances.

check if the unit receives standard gas pressure as rated on nameplate.

Make sure the regulator assembly on the gas valve is for propane. Sounds like the gas pressure is too low and the flames aren't going into the burner tubes. Make sure they didn't install an appliance regulator on the back of the fryer. This is not needed as the fryer has a regulator on the gas valve. You can unscrew the cap on the regulator assembly and turn the plastic screw inside all the way in. DO not turn with alot of force. Easy does it.
Tom

Flame is Orange? If so, propane is "choked", not enough air. Remove burners, clean each burner hole with a same size metal dowel (coat hanger works well) flush out inside of burner with garden hose, hi pressure air through all holes to dry. Replace burners ONLY after also cleaning chambers and chimney (garden hose and long brush). Do not forget to clean pilot light area too.
Most Imperials are pre-set air intake. Check gas pressure if able, 3" NG, 10" LPG. Good Luck

I do not know where you are located but if you have a restaurant supply or a repair tech near you they can get you a replacement kit for you

Is this fryer propane?It sounds like the baffles in the tank are clogged.If you remove a burner shine a light in the baffle,if you see alot of soot use a shop vac and clean it out.Let me know.

u must check the orfuse if the gas come out of that and u dont have flame u must adjest the air