[kd1221]

I have to second gallerytungsten's comment.

I've been approached a dozen times by business people offering me equity for my development time. I committed to and completed three projects and nothing ever came of them. Thankfully it only amounted to ~1000 hours among the three projects, but it's still time I wasn't paid for.

A technical co-founder with no work experience doesn't sound like much of a "technical" co-founder. Has he worked on any sort of open source projects, done research at a university, or anything that could be considered experience? If not, then it's not a good sign.

If you can afford to spare the time, then by all means take the opportunity, but I'd ask for 33% and wouldn't settle for less than 25%. Just state that you feel you'd be playing an important role in the product's creation and expect a more equitable share. You're allowed to put any price you want on your time. If they're confident the venture will succeed, then they should relinquish some of their share, otherwise they're being a bit greedy.