First time posting on here I’ve built 15+ of these bikes, have never had a reason to post before cause I’ve never had any issues I couldn’t figure out but this bike I built for my friend runs like crap with the air filter, when you take it off it runs fine. With the filter on it’ll run fine to a certain rpm/speed then it just bogs out super hard and would only go half as fast as the others I’ve built. When it was new and we assembled the top end we noticed a big gouge in the cylinder head (casting defect) and we thought that was the issue so we actually replaced the cylinder but it still ran the same so I was stumped, was going to swap parts out with ones from a good running bike till I found the issue I put the carb from another bike on it and didn’t bother putting on the air filter and took it for a ride to see if it was fixed and it was it ran good so I thought it had a defective carb but then I put the air filter on the other carb and it ran the same as before, switched back to the original carb but didn’t put the air filter on and it ran good. Anybody know what could cause this? Also by the way here are the engines that I use https://mobettabikes.ca/collections/frontpage/products/zeda-firestorm-80-motorized-bicycle-kit