It is possible that you've reduced airflow and made your mix richer, have you been keeping an eye on plug coloration before & after this mod?
Any obstruction in airflow will do this, mine was so negligible that I didn't need to adjust anything. Yet if you pull the plug and it's darker than normal you may need to move the clip on the carb's needle up one slot.
I would however support the PVC structure, prolonged use and vibration will surely cause you problems. Picture a 1lb hammer rapping away at yer carb lol and the leverage of the structure - if you grabbed it at the far end and gave it a wiggle. I try to build my bike and it's mods to withstand all sorts of misuse - like the gaggle of kids at the store that love to poke at my bike while I'm indoors, or like my buddy crashing it at 30mph o_O
One little thing - do you have a speedometer? It's a long shot, but when I did this mod to mine I thought I was going slower - but when I went home and got my GPS I found that I wasn't, it was just quieter.
I bet that it IS a lil restricted though, particularly if you squished the filter sponge. No big deal, we can get back to the fuel/air settings if that's the case
Just remember that running a lil rich is annoying but safe, whereas a lil lean it may harm the motor.
I like the pool drain tubing - heavier walls and custom color no less lol, but was it the wrong inner diameter to go over the carb like this?