Petromax HK500 can't get it to burn well

Bought a brass Petromax HK500, new, in 2017.
Lit when I first got it to check, but can't remember how well it worked. A couple of times since I've tried to use it camping and it lights to start with, although not very bright and within a few minutes the mantle is dim and sooty. Pressure is fine, and maintains on red line (pumping higher doesn't help). Raising and lowering needle doesn't help.

Have bought and replaced jet/nozzle and needle, replaced mantle, tried raising the J-tube & ensured it's not blocked, and filled with fresh paraffin and no improvement.
Seems like a rich burn with yellow flame.

The lamp hasn't burned for more than a few hours in total since new, so really can't understand what is wrong.

Hoping someone on here can tell I'm doing something stupidly simple wrong!

Thanks in advance.

First photo is just after lighting. It burns evenly but not very bright, a warm glow and comfortable to look at.
Second photo has been lit a while despite pressure still fine.

 

Welcome aboard!
As you have already replaced the jet then the most likely cause is that the jet is loose, sometimes the heat loosens the jet and one way of fixing that problem is to use some type of thread sealant.

 

Is the J tube getting very red when it does this. It sounds a bit like it is burning back in the tube.

 

I guess the pressure isn't OK.
The red marking is nice but doesn't mean anything, less then there is some pressure.

Remove the bicycle pump adapter use the hand pump and pre heat without pressure, after pre heat slowly pump air into the tank.
It also may be that you need to use the pricker more then once.

If not:
Check the jet for debris. Remove the top parts, pump up, open the valve and check if you have a steady, strait fuel "spay" coming out of the jet.