I have used some these kits without problems especially the metering diaphragms which I was getting from an US source for 0.94 usd. Now I do do got resource them as that vendor has closed up shop after 20 yrs.
I would not think related to the fuel pump (usually Mylar) or metering diaphragms since it will idle and this where these at minimal operation due to engine impulses are less active. Now I have seen a few kits (even OEM) where I need to re-adjust the carburetor after a few days as things settle in. It does sounds like fuel balance problem. Since I not there to put my hands on it; it is a lot harder to explain how these mixture settings interact with each other. Usually you tune low speed first and then the high speed but some adjustments are fine tuned in to get the best acceleration response.
