I don't know you any better than your co-founders and in general I would say that those who either 1) continue to finance or 2) continue to work should have much more of the equity than those who quit. If one or both of your co-founders leave, or if an investor doesn't follow up on his investments, you would want that party to have much less as well.

I feel bad for your co-founders that you guys haven't had a vesting schedule in place or similar so that you would lose most of your equity now when you quit. Imagine having to work for free or for low pay in the future just to hand over 1/3 of the result to someone else. I don't know if 10 percent is too much or fair. I

I know you could say that you have worked for 16 months for free or very little but right about now is when it usually gets really tough. Your savings are probably up, maybe you haven't found a product market fit yet, maybe there are no customers yet. Doubts set in, both in you and your partner, family and friends. Now is when it hurts to continue.

So right now, I think the decent thing to do would be to increase the capital by a lot and let the co-founders subscribe for those new shares but have the shares vest gradually as they continue to work.

I also think if would be a decent thing to let the possible investor know that you are quitting before he commits.