DO NOT LIGHT A PROPANE TORCH WITH A LIGHTER! USE A TORCH SPARK IGNITER!
Holding a small flame in your hand in from of a stream of flowing flammable propane (or MAPP, or MAP/Pro, or acetylene, etc) gas to light the torch can burn you. Don't do that. Use the spark igniter, if 'catches' a little bit of the gas to more easily ignite the gas and also gets your hand FARTHER AWAY from the gas and flame.
There is no more MAPP (
methylacetylene-propadiene propane) gas.
en.wikipedia.org
There are the yellow MAP/Pro cylinders, which have nothing to do with actual MAPP and are filled with propylene gas. Maybe 10% or so 'hotter' than propane, but not the same temp or heat level as actual MAPP (used in the same torch).
If you have a cheapo little propane torch head and compare that to a MAP/Pro torch head like a TS4000 or TS8000 torch head using MAP/Pro, then the TS4000/TS8000 is way hotter and puts out more heat but that is mostly due to the better torch head (bigger flame and the 'swirl' flame) and only a little bit due to the MAP/Pro instead of the plain propane.
A HD by me has/had some cylinders labeled MAPP in big bold letters, but if you read the label in the small print it states that they are filled with propylene gas (same as the Map/Pro). From an Italian/European company IIRC and not Worthington/Bernzomatic, and I was excited until I read the small print and it says that the gas is just propylene. IIRC, those cylinders were maybe $1-2 less than the Bernzomatic MAP/Pro cylinders one shelf up. Still 3x the price of a plain propane cylinder though.
I'm almost tempted to buy one cylinder and then sue the *&#%$ out of them for False Labeling and Emotional Distress because I miss actual MAPP gas and recently used up my last cylinder of actual MAPP.
TS8000 torch is awesome IMNSHO. Get that one if you are looking at a propane/MAP torch.
As to the OP, the gas didn't go bad. I'd guess that the cylinder valve is gummed up or 'stuck' or the torch head orifice is gummed up or clogged (dust, dirt, spider web, missing sock, etc). But you said you had the same weak pathetic almost flame with two different torch heads, so I'd say that the cylinder valves have mechanically gone 'bad'.
Get a brand new cylinder and try that. If it works with your torch, then the old cylinders have gone bad. Properly dispose of the old cylinders (burn off the propane and THEN dispose of the empty cylinder) and move on.
Note that there was a recall and whole bunch of mechanically bad Worthington propane and MAP/Pro cylinders around the 2012 time frame.
en.wikipedia.org
Unused cylinders: If the cylinder has never been connected to a torch or other device, do not use cylinder. Return cylinder to store where it was purchased for exchange or full refund. Partially-used cylinder currently connected to torch or other device:Do not disconnect torch or other device...
www.cpsc.gov
If you hear/feel the liquified propane sloshing in the cylinder, then there is liquified propane in there. And it's liquified because of the internal gas pressure. No need to poke the cylinder valve, except to maybe mechanically vent and blow out any dust/dirt/crud from the valve. Obviously do so OUTSIDE and wear gloves (cold venting propane and also the propane stink). And be prepared that if the valve is 'sticky' it might then get stuck in the open position and continue to vent the propane.
As to the refilling of a 14-16 oz disposable propane cylinder from a 20 lb (or larger) propane tank, IF you do that then the DOT and federal regulations state that the cylinder can NOT be legally 'transported' (it's on the label of the disposable cylinder in the fine print too) . The cylinder and cylinder valve and over-pressure relief are also made to a price-point and are not super durable. Hence they are disposable. You also have to fuss a bit to actually get a 'proper' charge from the 20 lb tank into the disposable cylinder without overfilling it (and causing the over-pressure relief valve to vent the propane and then not reseal). And the old trick of turning your 20 lb tank upside down to flow liquid propane into the disposable cylinder doesn't work anymore because of the OPD float in the 20 lb tank. Or so I've heard.
