Date registered: Aug 2005
Vehicle: 1972 250C, Ducati ST
Location: Norfolk, Virginia
Mentioned: 0 Post(s)
Quoted: 0 Post(s)
RE: distributor help 72 250c
I'm assuming that you're doing all this with the engine idling. If that's the case, disconnecting the vacuum-advance hose shouldn't cause enough of a vacuum leak to stall the engine. In fact, the vacuum-advance line should be connected to "ported vacuum", not "manifold vacuum", and the ported vacuum connection shouldn't have much vacuum at idle(less than 5").
To really figure out what's wrong and to fix it, you'll need a tachometer, a timing light, and a vacuum gauge.
With all the hoses connected, your idle should be 800-900 RPM in neutral once the engine's warmed up, and the stock timing at idle with the hoses connected should be set to 4 degrees after top-dead center (ATDC). Once you get everything sorted out, you can actually advance the timing quite a bit, but since you're having problems, you're better off starting off with the stock settings.
At idle, measure the vacuum at the vacuum-advance line at the distributor (should be very low), and also measure the manifold vacuum. You can test the manifold vacuum by disconnecting the seat-lock hard vacuum line (the dark blue one) from the rear of the intake manifold. The manifold vacuum should be at least 15" at idle.
As for the vacuum-retard lines, they're mostly for emissions-control purposes, along with the very-retarded initial igntion timing. Once you get everything sorted out, you can probably bypass them, but if they look good, you may as well leave them connected while you're troubleshooting.