Marelli Plex 201 (mechanical advance) information needed.

[kmoses]

I am looking for information on the Marelli Plex 201 (mechanical advance) distributor SM801AX. When I received it there was no information on the total amount of advance or at what RPM the advance occurs. Currently my ignition setting is 15 deg. BTDC @ 850 RPM idle and I have 30 deg. BTDC @ 3500 RPM. I have no idea what my total advance is. The car starts and runs great with just a little soot on the plug and a light brown color on the porcelain but before I fine tune the carb. (34 ADF) I want my ignition correct.

[baltobernie]

No model numbers given, but this may help.



Can you borrow a "dial-back" timing light from someone? With such a tool, you can plot your actual advance vs. RPM.

[kmoses]

I'm thinking the Marelli Plex 201 must have a different advance curve than the one charted. At 3500 RPM mine only advances 15 deg. but that is the type of information I would like to find. I have a nice Bosch digital timing light but it will not display the RPM and the dial back advance at the same time.

[So Cal Mark]

wow, that's a lot of advance on the marelliplex. I would expect some detonation with that amount of advance

[kmoses]

I found the following information on the Guy Croft site about the Merelli Plex 201 SM801AX 802r2:
Static advance: 10°
Automatic centrifugal advance: 24° ±2°
Nothing there showing how much advance at a giver RPM but if I am showing 30° advance at 3500 RPM then by 4000 RPM I should be at 34°max advance.

[So Cal Mark]

the graph must be distributor degrees, but it doesn't state that anywhere

[baltobernie]

The graph is from one of the veterans at Mira. I'm guessing the numbers are static + mechanical, as the Marelli electronic footnote is "@15°" and the yellow line starts at 15.

It's been a long time since I've seen a Sun distributor machine, where this type of info is available in real time. A rough approximation today requires two people; one to call out the RPM from the tach, while the other dials back the timing light to the static number at that RPM.

[fiatfactory]

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[kmoses]

Thanks Steve, I just saw your post. I have it set at 12° now and the everything seems good but I will try 10° and see if it gets better.

[fiatfactory]

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[kmoses]

If I was to rev. this engine to 5,500 rpm sitting still, I think it would grenade. Going down the road with the engine under load 5,000 rpm gets a little noisy, I'm thinking (hoping) the alternator bearings are the cause.