Use intake vacuum for vacuum advance at distr.?

[MunichTaxi]

The spec at idle is 4 deg ATDC, but at that setting, the engine has no power.
I plugged the 'retard' hose, set timing to TDC and got a little more power.

Then, I set the timing at idle to 15 deg BTDC and got more power from the 130.92 engine. No 'pinging' noises were heard.
But it still is not quite right. Since I have no way of testing vacuum advance under load, I am still baffled.

I think I am having trouble with the vacuum advance signal from the 3 way valve. Can I run a hose from the intake manifold port (near cyl #6) directly to the vacuum advance port on the distributor?

[Tomguy]

I don't know about the M130, but with the M116/117, at least with DJet, the vacuum source for the dizzy is AT the throttle plate. When you give it gas, the throttle plate will open, and the vacuum will be drastically cut with the more you give it. I would imagine this is an important part of your engine too - but I don't know where your vac is supposed to be sourced from. Make sure it sucks strong enough to retard it at idle!

Another possible issue is that your mechanical advance mechanism is stuck, making it not advance at higher RPMs like it's supposed to. Check your distributor rotor - you should be able to turn it clockwise without too much force, and it should turn back once you let it go (almost all the way, if not completely). If it doesn't move freely, and you put a drop of oil in the top shaft where the rotor goes in, then I suggest taking the dizzy out and cleaning the advance assembly.

[230/8]

Munich:

TomGuy is right that cleanliness is an advantage which will help to rule out "Sticktion" as a cause of your trouble.

With respect to vacuum and FI engines, there is no venturi as such in an FI engine, just a throttle plate where vacuum signals exist just below the plate but are highly variable because the opening and closing of the throttle valve. The most reliable vacuum signals are straight from the manifold and in fact this is the primary source for the V8s where it is tucked away at the back of the engine near the firewall, not at the throttle plate where it varies. The vacuum advance is taken below the throttle plate, for what reason I cannot say, but it seems to not affect how the engine runs.

Based on what you have indicated it seems that your M130 distributor operates like the one on the M117 V8 in my 350SL. The vacuum cannister retards the spark a fixed amount until a certain speed is reached, a temperature is exceeded, or the AC comes on and then the three-way valve cuts the vacuum so the centrifugal advance operates unrestrained to give the engine a bit more advance. The amount of the vacuum retard can be quickly determined by setting your timing by the book with vacuum connected and then watching the mark as you disconnect and reconnect the vacuum line.

I like the way my V8 runs w/o vacuum so I simply plug the line to the distributor and my engine operates great. It's not sophisticated at all but very effective. You might want to crank in a tad more advance in little bits, 1-2 degrees at a time if possible until you feel you've extracted all the performance you can.

To answer the question you raised, yes you can hook directly from the manifold, but then you lose the ability of the "system" to cycle the vacuum on and off according to those variables listed above. You'll probably be happier with no vacuum line to the distributor. As a side thought, any chance you can latch on to a euro-style distributor for this engine? It may make a world of difference in your satisfaction.

For what it's worth...

230/8

[MunichTaxi]

from a 1971 280SE, M130.98. Unlike the M130.92, it does not have a vacuum retard port on the diaphram module.

When I observe how far the advance rotates (by pushing on the plate), it is twice the advance range of the carburetor version, M130.92. The carb version is restrained by the limit of the 'arm'.

I tried to swap the advance diaphrams on the 2 distributors, but the mounting plate screws don't line up.

Right now, I don't think I am getting any vacuum advance from the 3 way valve. I WILL TRY 250_COUPE'S METHOD, AS OUTLINED BELOW:

On my 250C, I disconnected the three-way valve completely and routed the vacuum line straight to the advance side of the dizzy. There is only 4 degrees of advance in these dizzys but I figured some is better than none. I set the timing at 40-42 degrees at whatever RPM the book called for.

And futher explained by Arthur Dalton:

The idea is to set the 3000 rpm timing as that is at the top end of the mechnical advance . If there is a 20 degree mechanical advance , then when at idle rpms, the car will be at 10 BTDC... but if you have manifold vac and bring this to the retard section of the vac device , when the carbs are closed , the vac retard will bring the idle timing down closer to TDC .But, as soon as you open the throttle, the retard will collapse and you will get advance. So, this gives you are steady idle at around TDC , about 10 degrees off idle , and full advance at 3K