yep you guys are correct, brake cleaner is caustic and when burnt has very unpleasant fumes and those fumes can be harmful if you breathe them in directly or even indirectly.
And on that note i would say that starting fluid would probably be the best of the 2 mentioned but either one has its consequences if not used correctly.

Too much starting fluid and u lock up the engine and have to wait for it to dissipate before it will turn over again and in some cases it has a very bad reaction to aluminum pistons if used too frequently so that is why i said to use a light spray in the air cleaner only, NEVER spray it directly into the intake.

As for the brake cleaner i only mentioned that because it will run an engine if you do not have any starting fluid handy but like has been said... it has a very caustic pungent odor and will mess your lungs up pretty bad fairly quick if you breathe it in. So if you absolutely have no other choice but to use it i would do it in a very well ventilated area. Outside preferably :o)

and as for that article rcav8tor posted about that guy breathing in the vapors from the burning fluid on the diesel fuel tank, i'm sure that was not very good but there were alot of other factors that may have contributed to his condition like when welding there are certain gasses that can be produced even with no cleaning solvents being used that are generated from the heat and reaction to the metals themselves. The diesel tanks may have had coatings on them or a certain type of paint, and if they were galvanized that would have been very serious as galvanized metal produces poisonous gasses when heated and melted from welding, bad enough to kill you in just the manner he was describing.
When i worked for a cat dealer where i live we had a welder in our shop that was welding on some frame components and just the paint that was on the frame when burnt from the welder produced a toxic gas and it had such a bad effect on him he was sent to the hospital within 30 minutes, he fell out on the floor and almost died right there.
So yep i do agree there are many things that can have adverse effects on you that most people take for granted.
I myself am fairly fortunate i suppose, i have never had anything remotely like that ever happen to me over the years other than a bad headache from breathing in some of that crap on occasion.
I guess it can happen to anyone though and none of this should be taken for granted.
ALWAYS BE SAFE! and don't take ANY chances if you are not sure of what you are doing.

The chlorinated brake clean will do a fellow in and i highly reccomend not using it for anythng that has to do with combustion. This stuff will turn from friend to foe in a matter of a second. Heres a link ://tomwade.me/motorcycles/phosgene.php Just place HTTP in front.

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"voice of experience" here...
don't breath the fumes of burnt brake cleaner (like walking through the exhaust smoke), you could find your self in the hospital with a rash like thing on your throat that causes your gag reflex to not stop... they may have to knock you out and feed you through a tube for a week or so... not fun.
but everything else they say is dead on...

you should verify that you are getting LP to the mixer
it sounds like its just not getting enough fuel

you can pull the inlet line off the mixer and turn on the key to open the lockoff valve and then apply vacum to the filter assy to open the LP flow and LP vapor should come rushing out of the hose at the mixer. If you get a decent rush of vapor then you can troubleshoot it from there. Check the mixer diaphram and make sure it is intact, no holes or tears. Chamber is clean, etc etc.

Just because the lockoff is clicking doesn't mean enough fuel if any is getting through it. I have seen those go bad and keep a truck from running even though it could be heard clicking.

As long as you have air, fuel and spark the engine should run unless you have a timing belt issue or something like that.
Verify the timing is ok by putting engine on TDC and checking distributor rotor making sure it's pointing at #1 cylinder wire on the cap.(if it has this ignition system on it).

Or you can just do it the old fashioned way and pull a plug, leave it connected and turn the engine over and see if its got spark ;o)

And i'd be careful using ether (starting fluid) that stuff is evil and doesn't take much at all to flood the fuel system. When bb says a small squirt, he means a very small squirt. IF i ever use that stuff at all i generally just squirt a quick burst into the air cleaner (with air filter intact) It is usually enough to see if the engine is going to run or not. Brake cleaner works as a starting agent too and is not quite as reactive as ether is ;o).

Sounds like you may have flooded the machine & flooded LP is a real bear to clear.

Install new spark plugs (warming them to the touch with a hand held torch can help) & turn off the LP tank & purge the fuel system. Then give her a little squirt of either & see if she fires. This may take a few tries depending on flooded she is.

If she doesn't fire, then a complete check of the ignition system & a compression check would be in order.

If your sure the ignition system is good then your not getting fuel. It should fire with quick start. Had the same issue today, bad valve seats in head, wouldnt build any compression or generate any vaccum to pull fuel in.