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It's a honda ruckus gy6 swap. So the gas tank is in the floorboard, down low below the height of the carb. But the same fuel delivery I have now worked perfectly fine with my old 150cc stock gy6 engine. It never flooded the carb back then

What's the difference between a floor tank and bottom tank?

I recently upgraded to a 180cc big bore kit for my GY6 ruckus and I am noticing the carb is constantly overfilled, which is evident by the excessive fuel pouring out as soon as I loosen the screws to the carb bowl and the fact the overfill tube is always full of gas.  The scooter will randomly cut out when I am cruising mid-throttle.  I am running an OKO 30mm D-slide carb, which is brand new, and I made sure the needle and seat are working properly. 

I currently have a round Mikuni DF52-21-D dual output 35L/hr pump installed, with both fuel outlets T'd to a single hose that runs to my carb.  Does the stronger vacuum pressure at the intake manifold of my 180cc engine increases the fuel pressure or flow rate the vacuum pump operates at? 

The fuel delivery setup I have now is the same setup I used with my 150cc and I never ran into flooding or overfueling the carb.  In fact, I had to use the Mikuni dual output setup because the rectangular DF-44 single output Mikuni pump wouldn't be able to provide enough fuel during WOT sessions.  I would actually run the carb bowl dry only after a few minutes of WOT.  Once i switched to the Mikuni dual outlet pump, I would be able to WOT all day and not starve the carb of fuel. 

Now it seems with the 180cc build, it's the opposite problem of overfueling.  The first thing i tried was installing a vacuum restrictor (basically a hose coupler with a small hole restrictor inside) inline between the pump and the vacuum nipple on the intake manifold.  I thought by restricting the vacuum, it would lower the pressure or flow rate of the pump.  Turned out it didn't change anything.  Carb was still getting overfilled just the same.  Again, i verified the needle and seat are working properly.

One friend recommended I switch my vacuum line to a smaller diameter line, but seeing how the vacuum restrictor didn't make a difference, I don't see how changing to a smaller diameter vacuum line would help either.

Would switching back to the single output 14L/hr Mikuni pump fix this issue?

The spark plug looks fine, nice golden brown, no where near white like the valve in the picture above.

After getting the exhaust header welded and fixed, I went for a ride, during a short WOT session, the engine all of a sudden loss power and stalled out, I thought I heard something breaking/rattling. The scooter wouldn't start after that, it would still crank and produce spark, but wouldn't start. I had it trucked back home and I examined the CVT transmission to make sure the belt and transmission components were ok. I also checked the valve gaps and both were set fine.

The following day, the scooter does start up no difficulty, but as it idles, I hear this intermittent metal knocking noise coming from the engine, as shown below in the video. I examined the transmission side to ensure everything was spinning fine and nothing was out of balance. Crankshaft is spinning true. I can still ride the scooter just fine, but it does make that metal knocking noise just like in the video. There is no loss in power or low-end torque and I did a compression test and it showed 145 PSI, so I believe compression is still good. Acceleration is good too.  While I do hear the loud metal knocking noise, I don't feel any unbalanced vibration when riding. 

But I know something broke during that last ride when it all of sudden died, as it didn't have this knocking sound before.

I just replaced the crank seal the same day.  I made sure the crank was perfectly smooth and that the seal was properly installed and greased on the inner lips.  The seal is perfectly fine.  I cleaned the inside up so there were no oil residues left.  After riding with the freshly installed seal, I took off the CVT cover and oil was leaking right from the yellow plug.  The area around the crankseal is perfectly dry and free of any oil or oil trails.   

There must be a reason why the factory put a yellow epoxy plug there, as if to seal something off.  Otherwise, it would be totally random for them to put epoxy in that hole.

Nope. Both engines were obtained from different sellers.  There's another rider here, which I posted a pic of his variator area above and he also has the yellow epoxy covering the same hole.  Has to be more than a coincidence.  I know there are different versions of the GY6 engine (157QMJ, 1P57QMJ, etc)  I'm not sure what is the difference between the different engine codes.

There is oil leaking out of the yellow epoxy-covered hole next to the variator.  I recently replaced the oil seal again and made sure everything is sealing properly.  If i push on the yellow epoxy part, I can see oil being forced out around the edges of the epoxy.

What is the purpose of hole the epoxy is sealing?  Can I remove the epoxy and just fill it with JB weld?