W123 ignition timing woes
 

Hi folks,
after replacing my timing chain on my 83 230CE I decided to set my ignition timing. As I didn't have a timing light I used the by ear method and the difference it made to the running of the car and the fuel economy was huge.
While I was setting it I pretty much moved the distributor from almost fully turned clockwise to almost fully anti clockwise.
In the interests of setting it up more accurately I invested in a timing light. I looked up the workshop manual and see the setting for my distributor at idle with the vacuum attached is 3 degrees btdc. I dialled in 3 degrees on the back of my light, turn the dizzy so the tdc mark lines up with the pointer and now its back at almost fully clockwise again and running crap. I retarded the timing about 5 degrees more to allow for the 95 octane petrol we have here but it's still running a lot less smooth than it was.
Any ideas?

Sounds to me like maybe someone has changed the vacuum lines around in some way that you have manifold vacuum on the dist but the specs call for the vacuum to be ported (no vacuum at idle). If you have vacuum at the dist at idle, then unhook and plug the line then set the timing to 3 deg. Reconnect the vacuum and drive the car and see if it pings under load. If it does then retard the timing 3 deg making it TDC and drive again.
What market was the car built for, USA, Euro, World? This will make a difference. My 500 engine was made for the Mexican market (I think) and is a low compression engine and runs better on regular than it does on premium. I don't know what the official spec calls for but I run it at 7 deg btdc.

PaulM

Thanks Paul, I tried your suggestion but the difference is marginal unfortunately. Disconnecting the vacuum made very difference to the timing. My car is a euro spec and here in Ireland it's very hard to get any other fuel than e85.

Another thing I noticed is no matter how far I advance the timing I don't hear any pinking. Someone suggested to me the dizzy was on the wrong tooth but surely if cylinder no 1 is firing 3 degrees btdc I should be in the ball park for correct timing?

Are you saying you have to burn E85 as in 85% Ethanol? If this is correct, you are lucky the car runs at all. I don't know what to tell you. These cars weren't designed to run on ethanol.

PaulM

No sorry I got that backwards, it's E5 :)

Thats good news. We have E10. Ethanol-free is avaliable in a few places but hard to find. I loose aprox 10% power and 10% mpg. I have to change the mixture and timing for the different fuels so I just use the E10.
I would just set the timing to 8 deg (3 + 5) and drive it to see how it does. If every thing seems to be OK then try 13 deg. You can go higher but I wouldn't go over 15 deg. Then choose the one you like the best in terms of idle, mileage, power, and smoothness.
Now that you have a timing light, check the mechanical advange and vacuum advance. Disconnect the vacuum advance. Raise the rpm to about 2000 and see what the timing is. It should be maybe 20 deg or so. I don't know what it will be for your car but it should advance some. Now re-connect the vacuum and do the same thing and you should see even higher numbers. Maybe 40 deg or so. I don't know what either of these readings will be but as long as they are changing when you rev the engine then we know they are working.

PaulM

I've been playing with this for a few days now, I checked the timing at 2000 rpm and as hoped it changed both with and without the vacuum and by different amounts.
I've had it set at 15 degrees for a few days and it's running better than it was however twice now when I was turning the engine off it ran on for a second or so before cutting out.
Just out of curiosity I turned the distributor to where the idle peaked and ran smoothest and measured the advance by turning the dial on my light until I got Tdc showing. It was at 35 degrees, is this normal at all?

timing with vacuum applied should be in the 30s. I dont have your specs, but they are all like that. See Car won't start Steering wheel lock? - Mercedes-Benz Forum

Also, does your timing light indicator agree with the crank pointer?

Hi Hirnbeiss, are you sure they should be in the thirties? It would help if they were :)
I have a w123 workshop manual and it says 3 degrees. On the back of my timing light there's a dial that I turned to three degrees or now 15 degrees. I then pointed it at the crank pointer and turned the distributor until I saw the pointer line up with the TDC mark.