Has spark, compression, fuel and air but still wont start
So a friend of mine has a 2003ish eiger 400 4x4 that was running one day, and the next morning wouldn't start. I figured it was just a carb issue, so I cleaned the carb, and still wouldnt start. I have a big bear 400, so comparing to the pull start on that, the eiger seemed low on compression. I checked the valves, and the clearances were a little tight. I got them in spec and figured this would fix the problem. I was wrong. I took the carb off and sprayed starter fluid straight into the intake thinking I may have missed something in the carb and it wouldnt even hit. I pulled the plug to check the spark, and it was getting good spark. But something seemed a little off about it. What it seemed to be doing is sparking once for every stroke of the piston. Intake, compression, power and exhaust. 1234. 1234. Instead of what I'm used to with it sparking once to ignite the mixture at the top of compression and a wasted spark on the exhaust. 12. 12. The battery was really weak, so I had been jumping it off of another fourwheeler and even a car at one point through all of this. I thought there may be a shorted cell in the battery causing a problem. When you put a voltage meter on the battery and turn on the key, the voltage starts dropping fast, as in a normal counting rate, 12.50, 12.49... all the way down to 9 volts and then didnt come back once the key was off. Now when I compared this to my big bear, it did the same thing but only went to 11.98 and held there, coming back to about 12.5 volts when the key was off. So I disconnected the battery from the eiger and removed it. I then hooked jumper cables to the big bear so as to cut out the shorted battery to hopefully fix my problem. The voltage didn't drop near as quickly or as far, but the spark remained the same. The best I can figure out is as the air fuel mixture is being brought in on the intake stroke, the extra spark ignites it and it burns before it has a chance to be compressed. I got it to hit one time by spraying starter fluid in the spark plug hole while it was on the bottom of the compression stroke, so when it came up it fired. This is what lead me to believe what I said about igniting early. I'm getting pretty frustrated with the whole thing, and I've checked most everything I know how to check, so I made a profile on here to try and get some help.