How to correctly set timing on 107??

[Bondavi]

My car keeps having too far advance when under revs. I changed out the ignition distributor to rule out the springs, but no luck.

Do I set timing at idle WITH or WITHOUT vacuum connected?

Assuming vacuum connected, I set at 16 degrees BTDC, but when I rev up to 2800 rpm it goes to 35-40 degrees, not the spec'd 25 degrees!

What the heck?! What could be the culprit? Vacuum routing? No vacuum leans as far as I see, idle is nice and steady.

[Bondavi]

I tested spring lash in the ignition distributor by disconnecting vacuum advance, setting to TDC at idle, and at 3000 rpm's I'm seeing 25 BTDC.

So, with vacuum connected, I get 16BTDC and 40 BTDC at 3K rpm. The advance diaphragm under vacuum load is supposed to narrow the gap and allow 25BTDC under 3K rpms?

Assuming this is normal, is this something that the advance diaphragm regulates? There should only be 9 degrees difference in advance between idle and 3000 rpm.

David

[Roncallo]

Check your timing at idel With Vacume, but remove vacume for checks at 1500 and 3000 RPM. It sounds like everything is perfect from your 2 posts.

John Roncallo

[Bondavi]

So timing is spot on if it is 16 BTDC connected vacuum at idle, but 25 degrees at 1500-3000 rpms disconnected??

So I'm getting 40 BTDC at 3K rpm vacuum connected, that is correct, no?

[page62]

Here's a technique that works on Chevys, Fords...and Mercedes too!

Disconnect your vacuum advance. You want your timing to be about 36 degrees at full advance (the rpm at which it advances no more, probably 3000 rpm). Reconnect your vacuum advance and test drive. If there is pinging, retard the timing a couple of degrees. Repeat as necessary. Don't worry about initial timing.

This procedure assumes you don't have smog testing. (Factory settings are based on emissions requirements.) And it's only for non-computer controlled ignition systems.

Here's a link to a tech paper. Although it's written for Chevys, it works just as well on Mercedes (I wouldn't suggest something I haven't done myself...)

http://www.corvettefaq.com/c3/HowToSetTiming2.doc

[Bondavi]

You bet I am going to do that AFTER the smog test. The shop nitpicked and said my timing was set at 20 BTDC, too high, should be 16. Whatever.

Got too high NOx readings (they test NOx here), so I adjusted the air/fuel mixture 1/2 turn clockwise and am running the fuel additive to remove carbons from the system. Yes EGR works fine.

Does the mixture screw apply ONLY for idle, or does it apply for the rest of the rpm range except WOT?

David

[Roncallo]

Originally Posted by Bondavi

So timing is spot on if it is 16 BTDC connected vacuum at idle, but 25 degrees at 1500-3000 rpms disconnected??

So I'm getting 40 BTDC at 3K rpm vacuum connected, that is correct, no?

You dident post the year, model (country) of your car so I dont know the correct values. If you give me the year and model preferably the engine code I can get you the specs. But every thing sounds about right.

Proceerure is like this

Set static timing key on engine off as spscified usually about 10°
Disconnect vacume check at 1500 and 3000 RPM usually about 27° to 30°.
Connect advance vacume only and recheck at 1500 and 3000 again there should be a gain of about 8° to 12° (total 35° to 42°). Adjust vacume advance to correct. It I recall that is done with springs and shims.
If I recall the idel vacume chack is done with the retard vacume line connected and advance removed. Change of timing from no lines connected is about 5° to 10° retarded.


John Roncallo

[ctaylor738]

Do you have an O2 sensor? If so, what is it hooked up to if you have no lambda?

Could you post your CO, HC, and NOx results from the test?

Thanks,

[JoshC450SL]

I’ve read the whole article and sort of understand it. But with the vacuum line plugged the timing advances.

What would be great would be a video
Upload to YouTube or something of the whole process.

My 74 450SL says it’s supposed to be set to 5 degrees atdc with vacuum connected. I’ve been dealing with an overheating issue believed to be caused by incorrect ignition timing. The AI internet searches says that advanced OR retarded timing can cause overheating… so I’m torn and stuck on what to do. Most of the videos I’ve found dealing with setting ignition timing only sets the initial timing. If I could see it be done I could better understand what to do when the vacuum line is pulled from the vacuum advance on my 74’ 450SL to set the timing….
Thank you.

The chart on the service manual says 10-14 degrees btdc 1500rpms and 18-22 degrees at 3000rpms.

I am no mechanic but I can sort of understand mechanics and how to take something apart and tinker.

[Frank Reiner]

How to correctly set timing on 107??

1) Follow the instructions given by page 62 in post #5.
2) After setting the centrifugal advance timing connect only the advance portion of the vacuum diaphragm unit. Leave the retard section w/o vacuum.