Get a 1/2 qt of 2 stroke oil or other cetane booster (Walmart stuff) in the tank. Get the motor fully warmed up...take it out for an Italian tune up...and I mean flog it running the gears i.e. 3rd gear mashed to about 4,300 rpm. The smoke will be a little embarrassing when you first beat it. Then it will significantly clear on the second or third pedal mashing.

You'll find when you get back from the flogging the motor will be far quieter.

The diesel purge may also help. I just did my annual 2-can purge and it seems to quiet the chatter down.

Your local fuel supply cetane numbers may be a bit low for the 603.96 motor. I find that raising the fuel cetane with 2-stroke etc calms the chatter. So I run four ounces per fill up.

I generally baby my motor so its a little unnerving for me to go out and flog it. But it likes it!!!

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1986 300SDL 440,xxx