90hp Johnson V4 Dieseling

[kdh1947]

I started my V4 earlier today and closed down the fast idle to no avail. The engine began to rev to extreme. I turned off the ignition, also the main battery switch. Still revving. Removed the top cover and all of the plug leads. Still revving. Pulled the fuel line and waited for it to stall out. Finally.
This engine has been a little difficult to start of late and has not wanted to idle smoothly. I am a mechanic so understand engines well, but I have never had this sort of problem.
Any assistance would be great.
Thanks
Ken.
I will wait till tomorrow to check for any replies.

[boats.net]

It's probably running too lean, look for air leaks in intake manifold or crank seals.