Am I wrong?

Ink, I don't see how helping a friend get his 4 wheeler started is an "obligation". Helping him would be a favor, but, you're certainly not "obligated to him. If anything, if you do decide to go help him, any "obligation would be on his part, not yours.
Besides that, if you don't want to do it, don't, but at least let him know that you don't want to. Rather than sitting there waiting for you, he will probably seek help, elsewhere.
You're not "obligated to do that, either, but it would be a nice gesture on you part not to keep him hanging.

I've found that people ask favors of others because they lack the skill to do it themselves, need some help, or are just too lazy to do it themselves. I'm sure there are other reasons, but for the most part those three cover thing. You have no "obligation" to help anyone, but, if you consider this person a friend, you should, at least tell him that you just don't feel up to doing it, this time.

Just my 2¢, nothing judgemental.