[Terry Stapley]

On my 418W, with MSD dizzyand 6al box, if you bring up the rpm to get full advance all goes well!! The problem is that it stays at full advance when you let the rpm return to idle. If you shut off the engine the timing then starts at where it should be and the cycle starts all over again.
A friend put the MSD in a distributor machine and everything works fine, timing advances and retards as it should, but put it back in the engine and the symptoms described above take place all over again.
The distributor gear is fine on the cam and the dizzy.
Any ideas because I am stumped??