"normal" engine vacuum and timing readings for a 250C? - Mercedes-Benz Forum

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post #1 of 1 (permalink) Old 09-01-2005, 08:54 PM Thread Starter
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Date registered: Aug 2005
Vehicle: 1972 250C, Ducati ST
Location: Norfolk, Virginia
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"normal" engine vacuum and timing readings for a 250C?

I just bought a 1972 250C with the 2.8L M130 engine. The engine runs great, but it sometimes has problems starting when hot (have to crank it for about 5 seconds). I'm also only getting about 15 MPG around town.

It idles smoothly at 800 RPM in neutral, but the vacuum reading is a steady 15", which seems a little low to me. All of the vacuum accessories work fine, and I don't have any reason to suspect a leak.

The ignition has been replaced with a Mallory electronic unit, and the timing at idle is 7 degrees BTDC. This distributor has no vacuum advance or temperature advance mechanisms, as far as I can tell.

The Zenith carbs have been replaced with a pair of Weber 32/36 units.

What should a "normal" engine vacuum reading be, and what's a good setting for the ignition timing at idle? The engine runs smoothly, and doesn't leak, smoke, or burn oil, so if 15" vacuum is too low, I'm going to start playing around with the ignition timing a bit to try to correct the hot-starting issue.

Scott Gardner
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