Date registered: Aug 2005
Vehicle: 1972 250C, Ducati ST
Location: Norfolk, Virginia
Mentioned: 0 Post(s)
Quoted: 0 Post(s)
RE: Trouble setting timing
Actually, the distributor rotation is clockwise, so rotating the cap clockwise will retard the timing, not advance it. I have the same engine in my 1972 250C, and the factory spec for the idle is 800-900 RPM in neutral. Also, believe it or not, the factory timing spec is four degrees AFTER top-dead-center at idle. 1972 was when the pollution-control era was just getting into full swing, and the excessively-retarded timing was a result. If power and/or fuel economy is your goal, you can safely vary the timing a bit.
If your engine is idling at 1000 RPM and 10 degrees BTDC, and retarding the timing even a little bit makes the engine stumble, then you may have a vacuum leak. Mine will continue to idle smoothly down to 650 RPM or so.
On the stock ignition, there are two vacuum hoses and a coolant-temperature sensor that will affect ignition timing, so you have to make sure you have the appropriate hoses and wires connected or disconnected when you're checking the timing.
The settings on my car right now are 7 degrees BTDC and an idle of 850 RPM in neutral. The vacuum reading is 15" at idle, which I initially thought was low, but talking to other people, I think it's pretty typical. I've got a Mallory electronic distributor in place of the stock one, so I only have one vacuum hose and no temperature sensor.
At 7 degrees BTDC, cold-starting and idling are perfect and there's plenty of power, but hot-starting is a little hard, so I may retard the timing a few degrees as an experiment.
If you adjust your idle, try to adjust the linkage that controls BOTH carbs, rather than using the individual idle controls on each carb. The last thing you want to do is mess up your carb synchronization while you're trying to get the timing set.