Carbs off eBay are garbage? Well some may be, but the ones I’ve bought are Zara carbs and they are identical to the carbs I take off. Can’t remember if I’ve bought a Walbro. I’ve had good luck so far.Cheap ebay carbs are garbage. If you are going to buy one, get the real deal.
Actually clean the carb, because most people don't.
I have a ported 350 and have ported several more. The stock carb is great and can provide plenty of fuel. Mine will do 13k in the cut, and has plenty of fuel.
I think it is a dirty carb or an air leak.