I have a engine kit on a mountain bike and the carb wouldn't fit so I order a offset (z tube)intake and I found a small leak in it,at the welds.So check all new parts in the kit or aftermaket.Who would think a new part would be bad.
I've seen two kinds of these - one is made from cut pieces welded together and is usually good, the other is made by cutting & bending the pipe, then welding to fill the cut area, this one often has small gaps at the weld.
