The large capacitance of the FET gate behaves like a near short circuit at the start of charge or discharge, so will pull the output voltage of the 4017 up/down drastically. You may find a gate resistor of a few kOhms is necessary.
Just want to say many thanks to everyone who helped out with this. Got it all working in the end, was some dodgy mosfets that was throwing it all out. Have attached a couple of images....couldn't seem to add a small movie of it.