Either its running on LPG/LNG/CNG or wood gas as the secondary fuel, either way I think it would be difficult to run that old of a vehicle on both. Like Tanprotege said it would help us all out alot if we knew your vehicles setup, we know it has 4 wheel drums which means its pretty old for one (or a model not sold in the US anymore) but knowing how the rest of the engine is setup would help us out tremendously.

1996 mazda familia pick-up brake problems
 

Hi there. I'm sorry if I have missed led you. But yes the car can run on two fuel systems but the petrol side is not working. Yet.
The gas regulator is heated by the car cooling system as gas works better when hot as the gas heats up it will change from a liquid to a gas vapour and then into the engine via the cab. No petrol will flow just gas vapour.
The car was like this when I got it some 5 months ago now. The brakes worked just but on close inspection revealed the flexible pipe to be in a very poor condition so I had them replaced by a garage close by.
Then all the problems started. And so it goes on.
The gas regulator is less than one inch from the master cylinder and get hot to as is so close. I have no idea how long this problem has been going on as the old owner only used it to transport tree and flower from his shop.
I hope this will give a better insight to the cars history and hope you will have some more ideas on what to do with it. I think some air trapped in the master cylinder and when it gets hot the air will expand and forcing the brake fluid along the pipe making them start binding. This make them get very hot and more heat more binding until there is no more movement in the master cylinder and they all jam up.
Well that’s my theory.
Any other seductions are welcome
:mad::):confused:

Ok put some aluminum foil around your master cylinder as a TEMPORARY heat shield till you can make one out of steel, do not make it tight leave it loose so air can flow around the master cylinder, this should block most of the heat from radiating from the regulator to the master cylinder.

Thanks, Swifty.

I would place a shield around the gas regulator. Leave some space for air. I would use aluminum, maybe from an aluminum can (or steal a sauce pan from the kitchen ;-)). Direct the shiniest side to the heat source. And I would put a heat shield around the master cylinder, again shiniest side to the heat source. I am thinking that 2 walls and 3 air spaces should be enough to keep the fluid from boiling. See if you can get a little more space between the regulator and the master cylinder.
Change the fluid with fresh one.

If you still have problems you could switch to Silicone based fluid. It is more expensive but it has a very high boiling point and you don't need to change it that often. If you go this route you must completely clean out the fluid you have in it now.

He has front drums as well so there is no bias valve in the system, IIRC bias valves are only installed on a vehicle when it has discs in front and drums in rear to lower brake pressure to the rears since drums are self energizing BUT there might be a residual pressure valve somewhere to maintain a minimum pressure in the lines so the springs dont force the wheel cylinders all the way in and this could also be sticking.