Timing setting help please - 1969 w115/220 gas 4 cylinder

[Frank Reiner]

Topher:

In your post of 9/17/12 you asked about the influence of valve condition and adjustment. Have you adjusted the valve clearance and checked the compression? If compression is low or uneven, it may be quite difficult to resolve the timing and idle issues you describe.

The distributor which you currently have provides approx. 20 degrees of mechanical advance, and 20 degrees of vacuum advance. The total advance which you observe, 40-43 degrees with the vacuum advance connected directly to manifold, is appropriate for the application. That total advance is observed in a low load condition, hence manifold pressure is low (high vacuum) and that much advance will not lead to detonation. When the throttle opening is large, and the engine is under load, manifold pressure will be high (low vacuum), and the vacuum advance mechanism will provide a measure of retard to bring the total advance into the low to mid 30s, which is safe. I would hold off using a "mechanical only advance" distributor, for to be safe under load, the total advance will have to be set in the low to mid 30s, and you will not enjoy the mileage benefit of increased light throttle advance.

[Topher39]

Good morning Frank, thanks for your input.

Valves - I did adjust the valves just a couple weeks ago, and I can tell they have not been adjusted in a long time - they were so tight! The car starts and runs so much better now.

I have not messed with the timing since adjusting the valves - time just has not allowed, and I needed to step away for a bit. With the car running much better I would like to get the most out of my setup. I need to go over the notes to follow the best way to set the timing with this vacuum setup. Your feedback is much appreciated and needed.

Vacuum Advance - I will have to take a few photos of the Carb I have so you may see what I am working with, I did not know if my carb with operate with my particular carb, as they are both non-stock for my year/model.

Correct Vacuum connection - I want to be sure I connect the vacuum advance to the correct port on the carb, if I have a correct port! I know I have one that gives constant vacuum, I would like to revisit to see if it does vary much using a vacuum gauge.

Bring it on! Tell me more!

[Topher39]

Good News - I got the old vacuum gauge out and one of the three ports off my carb does have a variable vacuum depending on throttle position. Max at idle, comes down a good bit when I blip the throttle. Will have to see how well it works under load etc.

Will readjust the timing to work with the vacuum advance and see what I can manage. Right now the timing is set with no vacuum.

Chris

[crojack]

Did you need a special tool for the valve adjustment? Was it difficult? The manual I've glanced at showed a special valve adjustment tool.

[Topher39]

Not at all, I used a simple open end wrench and it worked great - couple of tight areas to work around but I got it. Took a bit to figure out which way to turn to adjust but you get it after a bit. Some of the valve lifters were very tight, and took a real shove to get moving - I figure with age and lack of adjustment on a 43 year car . . . but what a difference when finished.

[Topher39]

Well my carb offers the type of vacuum for a vacuum retard distributor, I have a vacuum advance distributor - so I either have to replace the distributor with a vacuum retard distributor, or go with a NEW electronic distributor that does away with the vacuum all together as its controlled by a small computer with a range of ignition curves to choose from. New system from 123 is $420.

If I find an old distributor that fits my car I will need to refurb and will most likely get an electronic module to replace the points. . . .

$420 or goof around to get a used one working.

[Frank Reiner]

Topher:

Install a fitting in the intake manifold, and run a hose directly to the vacuum fitting on the distributor. The functioning will be the same as if the fitting were on the carb at a point downstream of the throttle plate. The manifold may already have a plugged vacuum tap that would be connected to the vacuum modulator in a car with an auto trans.

[Topher39]

I have the vacuum off the carb now that gives full vacuum at idle - but my distributor has a vacuum advance, NOT a vacuum retard.

Would a feed off of the intake manifold give me the same vacuum as I am getting now - full at idle, or would that feed off the manifold allow me to work with my vacuum advance distributor?

Chris

[Frank Reiner]

Topher:

If I have read your previous posts correctly, you have made your vacuum connection to a source that is always manifold vacuum, even though it is on the body of the carb, rather than on the manifold. Your description of the advance events that you have observed, both with and without vacuum, leads me to believe that your present distributor is indeed appropriate for your use. I find it irrelevant that it may or may not be "correct" for the year or the carb configuration; rather I would be concerned that it delivers the advance that causes the engine to run well. And apparently it does! Since it does not seem to be "broke", don't fix it. If you will, please reread my discussion in post #16.

[Topher39]

Thanks Frank, that simplifies things. In relation to post 16:

Valves done, did not do a compression test yet - the last mystery!

It is running pretty well overall, I will take one more crack at setting the timing with the Vacuum advance and the valves and write down all the specific numbers I get so you can double check me.

I don't care if my carb/dist are not stock to my particular MB model, just wanted to be clear for those referencing particulars.

Might just do a swap of the points to Petronics or similar e-unit and call it done.

Thanks Frank!

[Benz Dr.]

It would be nice if the ones giving advice knew a bit more about how these ignition systems work. You can't mix up VR with VA - it simply won't work right.

If you have constant vacuum at idle that drops off to nothing by 1,500 RPM or less, then you have a throttle body VR system.

If you have no vacuum at idle that increases as RPM's increase, then you have VA.

Another system used on MB engines has constant manifold vacuum and the vacuum is shut off using a vacuum switch over valve controlled by a speed sensor.

The fact that the vacuum drops off a bit while bliping the throttle means nothing to the function of the distributor. This has some affect on a VA unit but it's not considerable.

The best way to determine which system you have is to hook up a vacuum pump or gauge to the various ports and see what signal you have.
I would also check the distributor to see which direction the point plate is moving. With rotation is VR and against rotation is VA.

Installing a pertonix unit will only replace the points and it will have no effect on the operation of the vacuum system. I disagree with the notion that a 190SL mechanical distribuitor won't work properly. The advance curve is slow enough that you shouldn't expirience any pinging.

[Topher39]

The question all along was will this carb/distributor combo work, both non-original to my particular car. There was also a question if my distributor is an Advance or a Retard version - All of this has created confusion on all sides, hopefully I can re-center the discussion so we are all on the same page. I have had discussions both on this particular forum and privately, I can see keeping them all on the single forum would be more helpful and less confusing for all.

Benz Dr. and all those who would like to join in, here are some hard numbers on my vacuum signal, carb and distributor that are on my car. I don't believe that my Carb or Distributor are original to my particular 1969 w115.

Facts: Valves are now adjusted, new coil, wires, points, rotor & cap. Carb rebuilt with a complete gasket kit, oil filled. No vacuum leaks on carb, intake etc.

Dwell Setting is at 50 and steady.

Distributor IS a vacuum advance unit (plate moves against the rotation and timing advances when activated as viewed with a timing light).
The vacuum advance starts to move at 8-9in of vacuum and moves freely.

Vacuum at Carb is at 18 in. at 800 rpm idle - as the throttle moves vacuum stays pretty steady, dipping to 15 with a throttle blip, but coming back to 18 in. The vacuum signal is pulled off the first of 3 brass nipples/tubes on the carb flange, where it bolts up to the intake manifold mount. The other two nipples have no real vacuum to speak of during the movement of the throttle, from idle to full open. I have blown High Pressure Air in those 2 additional ports, they are clear and free flowing.

Idle RPM, Idle mixture Adjustment - At an 800rpm idle, the car seems to like to go no lower than 15° BTDC to run smooth, anything less and it does not seem as smooth and hunts a bit. (It is difficult to go lower on that setting anyway because the vacuum advance portion of the distributor hits the spark plug lead attached to the plug, preventing further rotation) Idle Mixture Setting - I have adjusted by ear the idle mixtures and seem to have found a 1/4-1/2 rotation on the bottom idle adjustment that the car likes - outside that range and the idle gets rough.

Timing Settings as of today (Thanksgiving)
Without Vacuum:
800 rpm - 15°
3000 rpm - 22°
4000 rpm - 30°
4500 rpm - 34°

With Vacuum Line Attached:
800 - 25°
3000 - 35°
4000 - 42°
4500 - 43°
5000 - 45-46°
At 6000 rpm, It seems to almost hit 50° - no more that I can tell.

For the past 2-3 weeks, I have been running the car (running pretty darn good) on just the mechanical advance, with the timing settings you see above (without the vacuum attached.) Seems that the vacuum is only adding 10° of advance, at least in the driveway with no load.


So, that is the stats, the scoop, the skinny. The car runs really well overall. It's not a race car, but it seems to have decent power and gets out of it's own way. Interesting the "two-stage" accelerator pedal, that last bit of pepal that you need to press harder to get really kicks the car in the but.

Let me know your thoughts and suggestions and any improvements. Thank you all for your input and time on this, I live in a MB vacuum in northern AZ so I tend to such this shared knowledge up on the forum like a sponge.

Chris

Carb Photo Attached for Reference

[Frank Reiner]

Topher:

Thank you, I agree with your pragmatic approach, and

Bravo! 98 points in the Concours d' Carburetor,

apparently somewhat less in the Concours d' Distributor, (in the view of other judges).

Overall, a good show indeed!

[Benz Dr.]

All the vacuum is doing is adding about 10 more degrees to your total amount. Which means the vacuum advance portion is pulled forward all the way and is doing nothing for you. It's giving you more total because you can't move your distributor any further at idle before you hit an obstruction. It's not really doing anything for you in real terms. You still have a mechanical only system moved that's been 10 degrees advanced by hooking up the vacuum.

You're still only getting about 20 degrees of advance which is why I thought you would be better off with a fully mechanical distributor. That unit would give you 30 degrees of advance and you can set your timming anywhere you like. If you run 15 degrees BTDC at idle it should give you 45 degrees at 3,000 RPM. That will wake it up for sure and you may find that you will have to dial back the timing a little bit.

[Topher39]

Benz Dr. I see your point and understand. The SL190 distributor with the mechanical advance is more than difficult to find, and expensive, but I realize I am not getting a full advance curve.

I did find a complete, brand new, electronic distributor system from 1-2-3 Ignition that includes the entire distributor, computer controlled with several curves to choose from, all tailored to the 220. Downside is the $420. Price tag . . . But that would take care of the entire issue, no vacuum to mess with, no old distributor, no points etc. I am sure the investment would be worth it, just a hard pill to swallow.

For now I will keep running with what I have and make the best of it. I have other things to accomplish on the car as well. (Also have my sons braces to pay for coming up!) I will do a compression test on the cylinders as well, I will feel better investing more into the car when I know if the engine has some decent life left (it certainly seems to). I am tempted just to bite the bullet and get the new electronic ignition and move on, the perfectionist in me especially.



I need to decide if I am going to keep the car long term term or take care of it for a while and pass it on. I'm enjoying the car so far, I'm sure I would enjoy it all the more with a new ignition system. (Sounds like I am talking myself into it huh! LOL)