Originally Posted by
Tank
I would say that because the fuel rod that is controlled by the diaphragm would only be allowing a set amount of fuel through, when it reached 3100rpm there was not enough fuel to rev higher, as a working diaphragm is pushed down by boost from the turbo the fuel rod moves backward, increasing fuel supply, if it doesn't move the rod will be in it's furthest ahead position and supplying that amount of fuel which was not enough to rev past 3100rpm, hope this helps, Regards Frank.