SC Ignition Timing

My engine should be timed with the vacuum advance disconnected. I assume that's the black vacuum hose (upper, right). I think the red, rubber (lower, left) hose is the vacuum retard.

Anyway, when I disconned the upper, black hose the engine idle increases dramatically. Should I then time it at this very high idle, or should I bring the idle down to set the timing? If so, I would then have to reset it to idle properly after reconnecting the vacuum hose.

I guess I should play with it more. I may have the advance and retard confused.


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'83 SC

I believe all Porsche specs call for the vacuum hoses to be hooked up when checking ignition timing at idle. I know it is the case up through the '76 model, but I haven't checked for later updates for the SC models ... that data is on microfiche, and a PAIN to hunt through.

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Warren Hall
1973 911S Targa

Don't bother, Warrren. I'm hoping to hear from someone who has done this. My car calls for an unplugged vacuume advance. There is a vacuum hose on both sides of the VA unit (one for retard). I believe the big black hose going to the top of the VA unit is the advance. I think both hoses, when unhooked, cause further timing advance, so it's hard to tell. Both hoses, when unhooked, increase enigne speed. I believe that (unlike most cars) the centrifugal advance in our cars continues to provide a curve, even after startup (cent advance usually goes to full advance on startup on most cars). I'm seeking to understand these things and thre are folks who already do. Anyone?

You have better things to do, Warren, than learn about my car so you can teach me.

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'83 SC

[ohecht]

Superman,

Did you ever get a good answer to this issue?

It is very confusing. My specs also call for the hoses to be disconnected. 82 SC USA

The idle speed increases as soon as they are disconnected. I have set the timing at 5 BTDC in this elevated idle condition, but I wonder if I am supposed to bring the idle down manually first.

Also, when I rev the engine to check the advance the timing marks move counter-clockwise. Is this right for advance? It seems backwards, since the 5 BTDC mark is just clockwise of the Z1 mark.

Finally, how do you verify the amount of advance at 6000 rpm, since there are no marks?

Olivier

[Superman]

Yes, I did. Disconnecting one of the vacuum hoses does nothing (at idle anyway), but disconnecting the other one makes the idle race. Do this, and then reach toward the back of the throttle body and turn the idle adjusting screw head (about the size of a nickle) until idle drops to the correct speed (950 or so). THEN set timing.

When you reconnect the hose, idle will drop and need to be readjusted. If you've timed your engine at a higher rpm, then your timing will be substantially retarded, I believe. IF this is the case, then when you set your timing correctly you will think your engine just gained 50 hp.

I do not have a fancy timing light with 'advance,' so I have not checked full advance timing. I am glad you asked about this though. I plan to put a mark on my crank pulley at the appropriate advance location (25 degrees, or maybe 28 or something) so that I can quickly and easily check full advance.

[ohecht]

My timing is definitely retarded then!

I guess I will go back out and get it set right.

Thanks, Super.

Olivier

[RoninLB]

My smog set up dizzy made me dizzy. Why would specs. call for 15 deg. ATDC in my '77? Looks very strange to me. The dizzy mechanical adv. puts out 36 at the crank. The vac. advance puts out 14 deg. at the crank. The engine ran strange at low RPM. It ran hot at idle and low RPM. Overwhelmed by simple cave man mentality I disconnected the vac. advance permanently and set initial adv. at 0. May not be perfect curve, never checked. Engine ran cooler and sharper with spark plugs looking good after adjusting CIS. Trivia

[marcesq]

Ron:

The 15 degree advance was for the '77 california model with thermal reactors, air pump, etc.

I think that you gave me the idea of plugging the advance, and setting the timing to Z1 when I first posted about removing CA exhaust system from my car.

After installing the SSIs, I ran the car without changing the ignition set up. Ran fine.

After a couple of weeks, I followed your hint, and if felt as if the car pulled a bit harder at the lower rpms.

[john walker's workshop]

unplug both hoses, which raises the idle speed, turn the idle back down to 950, set timing to spec, (5°BTDC), reconnect hoses and raise the idle back up.

[ohecht]

Thank you, John!

I wish Porsche or Bentley had bothered to print it that clearly on either the engine deck lid or the $120 manual!

Those of us raised on EFI are tough to train on timing.

I just set it correctly. Thanks to you and Superman.

Is it best to set the timing first, then the mixture, and then go back and check the timing?

Anyone know a good shop in Richmond that allows mixture setting with their EGA without a major production?

Olivier

[speeder]

John Walker's advice is simple and correct; only thing bothering me is that RED vacuum line is ADVANCE, and DARK BLUE, (looks black), is retard. At least if nobody has f'ed with 'em. Superman- I would look into this, make sure they are hooked up right. If I had the technology, (dig cam), I would post pic of locations.

P.S.: JW, is this right?

[john walker's workshop]

that procedure only counts for double vacuum distributors. the mixture has no effect on the timing of course. you can do it before or after. the only hose that has vacuum at idle goes to the retard, which will slow down the idle.

[ohecht]

My retard line is the blue (or black) vacuum line that is also covered with fabric braid. It connects to the distributor at a fitting pointing towards the right rear motor mount, just over the 13mm bolt that secures the distributor in place.

The other line is much more flexible, red, and the connection is pointing towards the other motor mount, about 90 degrees clockwise from the first connection.

The first line I mentioned slows down the idle when connected, and the second line has no effect at idle.

Olivier

[Mifintifin]

The Blue hose (looks black) is the retard and it should be connected to the inside connection of the advance diaphram (on the side that connects to the distributor). The Red hose (maybe black if someone replaced it, nobody has red hose!) is the advance and it is connected to the outside connection on the advance diaphram.

On 80 to 83's the hoses should be disconnected AND PLUGGED, but the retard is actually the only one that has any vacuum at idle. Since it has vacuum, it is retarding the spark slightly. When you remove it you get a big increase in rpm's for two reasons...1 it stops retarding, 2. you have an air vacuum leak. So plug the retard line (plug the advance line to, if you are checking high centrifigal advance). The idle will settle back down some when you plug the retard hose. Tweak the idle speed to 900 and time it to 5 degrees. Connect back up the vacuun hoses and set the idle speed again, because the retard is going to slow it down slightly.

By the way, if nothing happens when you pull your retard hose, then your distributor is screwed up and needs to be rebuilt. This isn't unusual, in fact it is highly probable. This model distributor isn't sealed and over the years lots of water gets into the lower end and corrodes the vacuum advance plate bearing as well as the centrifigal advance weigh pivots. (ask me how I know!). Another symptom of this is if your idle speed tends to hang up to high at stoplights for no rhyme or reason. (and you thought it was your auxiliary air valve, its not, its those gummed up advance weights.) Rebuild your distributor, many idle problems will disappear, IMO.

Mifintifin

82 SC Coupe
83 SC Cab

[Vipergrün]

Okay, need more clarification. JW says to disconnect the hoses and Mifintifin says to disconnect and plug. JW says 950 RPM idle, Mifintifin says 900 RPM. Which is correct? Sorry guys, not trying to start something here.....really

Thanks
-Brad
80SC

[john walker's workshop]

the factory says plug the hoses, but it really makes no difference. so what if there's a little air leak, it's the timing you're setting, not the mixture, and it's only for a moment. the idle speed just needs to be low enough that the mechanical advance weights retract completely. 900/950 should do it.

[Mifintifin]

John's right, plugging probably doesn't make any difference now that I think about it, but the Porsche Spec. calls for it. On the idle speed, the spec is 850 to 950 so I split the difference at 900.

Mifintifin

82 SC Coupe
83 SC Cab

[ohecht]

Is a silicone spray best for cleaning and lubing the distributor guts?

Or is that the place to use Bosch grease?

Olivier

[Mifintifin]

I wouldn't use silicon spray. Use bosch grease or even 3 in 1 oil. I use a combination of Bosch grease and 3 in 1 oil when I rebuild them. I any case, the centrifugal advance mechanism is down under the vacuum advance plate and just about impossible to get to from the top. There is an pop out inspection cap on the side that exposes the centrifugal stuff, but you can't really do anything unless the dist. is out. If a pinch, its probably better to just spray down under with a good slug of WD-40.

If you haven't had the distributor completely rebuilt, either do it yourself, or take it to a good wrench and have it done, first. Then, keep it lubed up on a regular bases after that.

Hope this helps.

Mifintifin

82 SC Coupe
83 SC Cab

[stormcrow]

Let me throw this out to you guys. Maybe a little thought into the subject will help.

Question - on single vacuume advanced systems - where does the vacuume hose connect on the air box - assuming you have fuel injection and what is its purpose?

Question - on the double vaccume advanced systems - where do the hoses connect to on the engine and why are there two? If connected properly, what does each one do and how is the vaccume on the distributor affected when the throttle is opened and closed?

Question - if the vacuume advanced hose is connected and it calls for 5 dbtdc how does this affect the advancment on the distributor when the engine rpm is increased? Does this make the advance mechanism 5 degrees greater than it would be if the vaccume hose was disconnected from the distributor and plugged at the higher rpm, or does this compensate for engine rpm on the top end when connected because the vacuume on the distributor can only advance the timing so far?

Just something to think about.

Steve