My distributor should be capable of providing 30 degrees of advance, and I'm only getting about 20. I think the vac retard may be staying engaged when the engine is revved to 3000 RPM. Here are the readings with vac retard line connected:

IDLE: 0 degrees TDC
3000 RPM: 20 degrees BTDC
(range of 20 degrees)

So I disconnected the vacuum line and this is what I get:

IDLE: 10 degrees BTDC
3000 RPM: 30 degrees BTDC
(range of 20 degrees)

Vacuum at idle measures about 16", and the vacuum is higher at 3000 RPM (measured at the distributor outlet on the venturi).

Is this normal? I thought the vacuum should collapse when the engine is revved - that would give me the 30 degree range I think I used to get.

Steve

AIUI, engine vacuum drops momentarily as the throttle is opened and the RPM's increase, but should increase and stablize when the desired RPM is reached.

Sounds to me like you do have a problem on the retard side.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Pull the advance plate in the dist [ scres on side ]. Easier to take dist out.
I think you will find a broken spring on the advance weights.
At 3K , the weights overcome and vac. retard, but one spring may not....
Also check the detent bearing/spring on the plate.

Thanks for the help.

The three way air valve has been bypassed; I assume that is OK?

I pulled the distributor and it appears to be in good condition. There are no broken springs on the advance mechanism. This is a replacement distributor (FastLane part #0.231.185.009), and possibly it never had more than 20 degrees of mechanical advance.

Are parts available to adjust the mechanical advance? If so, what are the best mechanical advance, and vacuum retard (advance?) settings for optimum performance on a 280SL?

Thanks,
Steve

Hi Steve

You may want to checl out this link http://www.durranceeng.com/IGNITION%20DISTRIBUTORQest.html They have a good F.A.Q.section.

Or you can email them with more specific questions.

Hope this helps

Bob

Steve:

If you car has the smog control equipment (70 or 71) , that is likely the issue. As I understand the system, the two way valve (vaccum box that looks like a bell-referred to below as the 3 way valve) is *suppose* to eliminate the vacuum retard at a 2400 RPM as actuated by the speed relay. Chances are, these are either not working or not wired correctly. Accordingly, the distributor continues to get vacuum retard through all RPM ranges.

I am looking into the same issue and am considering either a custom distributor solution or getting all of my relays to work. These relays are NLA new. I am told that even when new, the system did not work that well.

Regards,

__________________
Regards,

Tom S.
1971 280SL Tunis Beige Metallic
1971 280SL Tobacco Brown (13K miles)
1970 280SL Deep Red
1994 E320 Cabriolet
1999 E320 Wagon 4Matic
2002 LX 470
1992 Land Cruiser