I also had an XR6 and it was difficult to crank, until I finally learned the sequence of events to get it to fire easily. I see that youve pumped the bulb to be sure its tight. Next, youve got to hold in (push in on) the key for at least 10 seconds with the choke opened up as well. I used to count (1) Mississippi, (2) Mississippi, etc. The reason I did that is because if I tried to crank it too soon, it was a real pain in the tail to get cranked, but if I followed this sequence, I had no problem at all……assuming your starter is working. If Im not mistaken, in the owners manual, it says to choke and hold in on the key a minimum of ( seconds before you try and start the motor. I found that a little longer made it much easier. It feels like forever when youre doing it, but I found that that is what it would take. Mine was a 94 Merc 150 XR6.