Fore Firing?

I don't know if this is the right term for it, but when I got my 79 KZ750 twin going last, it's was like it was spitting into the carbs occasionally, when it catches I can clearly define the feeling while adjusting the choke. Back firing in the wrong direction? Igniting air/fuel somehow in the venturi?

Can carb adjustment be the cause for this because I do know it needs it, and it will be gettin it. My gut feel tells me it's in the timing tho. Anyone run across this?

Stock carbs, airbox, headers, sportie mufflers down low

Thanks!
springvinmoto.com/gallery/view_photo.php...album148&id=P1010001

P.S. Do you think the HD mufflers (cant wait to scrape them on pavement) will be as restrictive as stock?

If you have not done so already, clean (or replace) the points, and set the timing (after making sure the timing advancer is not stuck), check the coils also.
After all that if it still does it, then it's time to look at the carbs.
A 750 twin will start and run on one cylinder, you can even ride it that way (I have done it), it kinda lacks power though.

Does it run better when you apply the choke?

Thanks, all for your help. Once again, your great!