Here's a link that might give you some help.
Starting Bike
To add to what was said above, to prevent cracking the throttle while starting the bike cold, don't hold the throttle, instead hold the front master cylinder. Then you won't do the inevitable twist of the throttle, that tends to cause flooding.
Normally when you have to pull start a bike to get it to start, the compression is low. Just because he told you the top end was fresh, doesn't mean it was. It would be a good idea to check the compression.
If you can start your friend's RM, you should be able to start your YZ. If you can't, then there is something wrong with the bike that needs to be sorted out, rather than you wearing your leg out trying to light that bike off.