Hi my name is ***** ***** when you let these sit the fuel becomes unstable and then as it tries to evaporate then it will turn into varnish and freeze things up, as it likely did with the fuel pump. So you also have the injectors that that can suffer the same problem.
In the case here the injector might be stuck open and or not closing all the way thus allowing excessive amount of fuel to inter the engine.
I suggest to do a couple things here first, you really need to check the compression, if you don't have a compression gauge you can find a Harbor freight tool store and they have an inexpensive gauge, that will insure that the top end is doing what it should and you don't have a stuck valve as also stale fuel can do that also. Then compression if up over 125psi move next to the injector.
Since likely you will not be able to check the fuel pressure as it requires special tools, you can try removing the fuel injector go to a local auto parts store and grab a bottle of Techron (Chevron makes it) soak the injector in it and then with some Simple Green in a pot of water get it up to about 150 degrees and then soak the injector for about a half hour, remove the injector and then use a 9 volt battery to isolate voltage on and off, you can do this with the injector in the Simple Green solution, you might have to do this a few times and also maybe dip in back into the Techron solution, now this is all based on that the injector is clogged, but without checking the fuel pressure and then testing if its bleeding down we can only assume that this is the problem.
Let me know if this helps or you have further questions, please reply back and I will be glad to answer.