I've flown about 25 different 172SP's, and they've all behaved exactly
the same.

I open the throttle about an inch, and do the rest exactly by the
checklist. The only important variables seem to be:

- Make as little delay as possible between priming and turning the key
to START. It doesn't need to be immediate, but don't delay
unneccessarily.

- Advance the mixture from IDLE CUT OFF to RICH within a second or so.