I run a TM K9B and have switched to the short intake. The TM K9’s that I have seen had a collar that went on the carburator which then fit into the big carb boot that you describe. The short intake that I have from Green Flag Racing does not use this collar so I guess yours is missing. I also run mine with no return line or restriction in the main line but I do put a fuel filter just before the carb that acts also as a reservoir for extra fuel. The karts that I have used with a return line, we used the screw off top from the top of a spark plug inside the return line to create enough resistance so that more fuel pressure will go to the carb instead of the return line to the tank.