Is the fuel/air mixture screw supposed to have a spring? When I look at exploded view of the carby it has a spring but mine doesn't... It's a screw with a point and an o ring near the head of the screw and when I go to adjust the mixture nothing happens at idle It's not blocked I have pumped air through it and it's clear it just seems odd that it not having a reaction no matter how far in or out I wind it.