Heartbeat Effect with 74HC04 Suspended Bicore

I made a simple Suspended Bicore **broken link removed**

That has the heart beat effect going on, meaning it will "beat" like a heart (unstable duty Cycle). I was wondering if I should add come caps in series or across the output of it to smooth it out and make it more square. I grounded all the inputs, so that isnt the problem.

Thanks

See: AN118 from Fairchildsemi.com

I thought about doing that, I should have.