Help me diagnose this popping sound---with video

[almarconi]

Not saying it isn't leaking, but the gaskets are new

I think if you had an exhaust leak you would be able to hear it. Adjust the valves and sync the carbs before drawing anymore conclusions.

[pjm204]

If I can find a valve cover gasket locally tomorrow I hope to have the valves done over the weekend.

[renobruce]

47.5 on the pilots? Is that the stock size?

[pjm204]

stock is 45. I went up one size as per the recommendations from vance and hines

[chef1366]

Mess with the idle mixture screws until it stops. Too much gas. Use a portable tank or put your tank on a trash can or something above the carbs. Don't forget about the petcock vacuum line.
Sync the carbs after you get that adjusted.

[Gimpdiggity]

I think if you had an exhaust leak you would be able to hear it. Adjust the valves and sync the carbs before drawing anymore conclusions.

Not necessarily.

I had absolutely no idea I had a bad gasket when I was trying to fix the Ninja. It didn't sound like an exhaust leak at all...at least, not like any exhaust leak that I've ever heard.

What it was doing was sucking air in through a very small opening whenever the throttle plates were slamming shut. That air was then combusting in the exhaust causing the popping sound. It would do it primarily when decelerating, but sometimes would do it at idle and just off idle.

It's a phenomenon that's LIKE backfiring...only the opposite. I BELIEVE that the correct term for it is "afterfire."

But, if there's new gaskets in there, it's probably not the case. I was just throwing it out there as another option to check.

[almarconi]

What it was doing was sucking air in through a very small opening whenever the throttle plates were slamming shut. That air was then combusting in the exhaust causing the popping sound. It would do it primarily when decelerating, but sometimes would do it at idle and just off idle.

It's a phenomenon that's LIKE backfiring...only the opposite. I BELIEVE that the correct term for it is "afterfire."

What you are describing is usually caused by incorrect valve or ignition timing. If the pilot circuit were lean that could also cause popping but I don't think that is the case here.