Popping in inlet

[CaptonZap]

I installed a 100cc kit in a Kymco Sento 50, new cylinder and head, and took it for a break in ride. I was changing rollers in the variator, so I left the cover off of the filter housing. Once I got going, I heard a popping noise coming from the filter box, and it was loud, since I didn't have the cover on.
It wasn't  a regular popping, but random, sort of like pop corn when it starts to pop, increasing in frequency as the RPM's increased.
The valves are set at .004in clearance, since I didn't know how much the new valves would settle in, and I didn't want to take a chance that they would close up.
Does anyone have any ideas as to the cause of the popping?
Thanks for any suggestions.

CZ

[big blue]

Sounds like it is back-firing through the carb. Is it possible that valve timing is slightly off? I would recheck the valves and make sure that the timing marks line up. You might also reinstall the filter cover to see if the pop goes away. Sometime the intake needs a bit of restriction to work properly also recheck the seal on the inlet manifold you could have a vacuum leak.

[CaptonZap]

Sounds like it is back-firing through the carb. Is it possible that valve timing is slightly off? I would recheck the valves and make sure that the timing marks line up. You might also reinstall the filter cover to see if the pop goes away. Sometime the intake needs a bit of restriction to work properly also recheck the seal on the inlet manifold you could have a vacuum leak.

Thanks Blue,

I will dig back in and check the sealing at the manifold insulation spacer, and the timing, when I re adjust the valves after the break in mileage.
The popping is still there when the filter cover is on, just muted, as can be expected. When I first heard it, I thought it might be the exhaust, but after I ran it with the filter cover off, it was very noticeably coming from the intake.
I appreciate your thoughts,  JR