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backburning part 2
Posted by: (
Date: August 22, 2007 03:39AM

Still having problems.

I reckon there is a too rich mixture.

what kerosene fuel pressures are people running on 740's?
What is the diameter jets for the main burners?
what is the distance between the end of the jet and the mouth of the venturi?
Without droppng the burner assembly, is there any way of checking the burner for blockages? airflow? etc etc.



Picture of jets.

Edited 1 times. Last edit at 08/22/07 05:34AM by Jeff Theobald.

Re: backburning part 2
Posted by: Jeff Theobald (Moderator)
Date: August 22, 2007 04:45AM

Hi Dave,

A mixture that is too rich should not affect lighting back; Jet size will be affected buy a number of things,

Is your kerosene rated at 28 sec?

Your fuel pressure should be between 100 to 140psi, the higher the pressure the smaller the jet you can get away with.

The closer the jet face is to the venturi the richer it will run, a good guide is the jet face being about the same distance away from the venturi mouth as its diameter, your pictures shows this to be about right.

If you start with a fuel pressure of 100psi then jet size will be from around 40 to 50th, start with 40th this should give you a good clean fire, but maybe down on best performance, but you can experiment with that later.

If your burner still lights back, then you will have to drop the pan, after all the time this car has stood I would think it will be covered in all sorts of muck, from fire cement, ash, soot, etc, a good clean, check for cracks, oversize holes etc, clean all the tubes with a flue brush, vacuum out the smoke box.

Remove your branch forks, pull the vaporiser wire, and make sure everything is clean and free of carbon; there is a way of cleaning your vaporiser using oxygen. With the vaporiser stripped of fittings, connect a tube from a regulated oxygen supply to the fuel in end of the vaporiser; keep clear of the branch fork end!! With a blow lamp heat the vaporiser in the area just inside the burner where it is first exposed to heat from the burner fire, until red hot, turn on the oxygen just enough to get sparks popping and banging etc from the branch fork end, remove the heat from the blow lamp, watch the vaporiser very carefully, if it starts getting to hot reduce the amount of oxygen, you will see the hot part start to move along the tube, keep the point of reaction red hot, if you let it get to hot it will burn through, also watch the rest of the tube, I have seen a second reaction start further down the tube, which can catch you out. When the process has moved all the way to the end, you vaporiser will just need a blow through with compressed air, and will be perfectly clean.

Try this out, set the adjustments as I have suggested as a starting point, a good fire needs a clean system, hope this helps, Jeff.

Re: backburning part 2
Posted by: (
Date: August 22, 2007 05:57AM

thankx, now I have a few days play ahead.......

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