If its a fast leak - sounds more like the exhaust valve is leaking due to it being worn or there being crap on the valve. Also if you are running really low on air in your tank there might not be enough pressure for the valve to seal.
Take the LPR off and tap the body until the valve stem drops out. Give it a clean and a lube it with some thin oil and reassemble - for more info, check the manual out as its really good for troubleshooting.