engine miss

[tater 1602]

I have a mercruiser 5.0 1993 alpha1 gen 2 that once in a while it is like some one turns the key off and back on in a split second rpms drop from 4000 rpms and drops to 2000 rpms or so then goes back up to 4000 rpms in a matter of a second then runs good for a while and it might do it again 5 minutes later .also diesels for 5 seconds or so when I shut it off after running it a while .had new distributer installed last year . any help please . thanks

 

[QBhoy]

The monetary loss in power could be a few things including bad earthing or battery connections. Shift interruption switch dodgy.
The running on after ignition off is usually a water in fuel related issue. The latter could be both your problems source.

 

[alldodge]

I have a mercruiser 5.0 1993 alpha1 gen 2 that once in a while it is like some one turns the key off and back on in a split second rpms drop from 4000 rpms and drops to 2000 rpms or so then goes back up to 4000 rpms in a matter of a second then runs good for a while and it might do it again 5 minutes later .also diesels for 5 seconds or so when I shut it off after running it a while .had new distributer installed last year . any help please . thanks

I would look at the carb and fuel pressure. Dieseling is caused by to much fuel and incorrect timing. The rpm issue can be fuel pressure. Your pressure should be 3 to 7 psi.
Remove the fuel filter and dump contents into a clear container to see if there is anything but clean gas

 

[Bondo]

Ayuh,..... Welcome Aboard,...... Figure out Why it's dieselin', Before ya go out again,....

Dieselin' can Kill yer motor in that 5 seconds,.....

That last sputter, where the sound changes, just before it finally dies,....
Is the motor spinnin' Backwards,.....

The odds are extremely High that water will be sucked up the exhaust, fillin' a cylinder, 'n bustin' the rod when the piston comes back up,.....