I used to push my forks down till the clip on the top hit the clip-on. That will work good if you still have thoses clips on the top (small ring looking thing)

 

ok sooo i went out and looked at my forks...good lord both of them sliped....i couldnt tell cause im rockin fi clipons....thanks again everyone

 

Cool, I have the same problem whenever I try to catch idle my bike wants to do a circle even though im perfectly straight. I did mess up with my forks cause my bars were not aligned with the front wheel. I may have not adjusted it straight enough. I didn't think your forks could affect your wheelie at first I thought it was a joke but it makes sense when u cut your wheel on a circle it does make a lot of differenc