"I am not sure how to set the advance to 0 since that requires an idle of 950 correct?"

A process called "dead timing". This sets base timing with the engine OFF. There are several ways of accomplishing this. This is one method:

Rotate engine manually so the 5ºBTDC mark on the pulley (or TDC or whatever timing is desired) is opposite the split in the crankcase.

Loosen distributor hold-down/adjustment bracket.

Remove coil wire from distributor cap and position it close enough to ground for a spark to jump. You can also use a timing light in place of the loose coil wire.

Ignition ON.

Grasp only a portion of the distributor housing. Rotate clockwise about 20º, then rotate CCW slowly until spark jumps to ground. Stop.

Tighten dist. hold down clamp.

Timing is now set to 5º BTDC. If engine is ON and the idle speed is below 1000 rpm., the timing light should confirm the dead-timed adjustment.

Hope this helps,
Sherwood

Jeff, I have tried to follow it as close to the letter as I possibly can! To wit:

0) changed oil and filter, cleaned screen

1) replaced air cleaner cartridge and checked all air cleaner gaskets
2) had compression tested, checked out fine
3) replaced plugs and gapped appropriately
4) replaced points, rotor, cap and set dwell
5) checked and set timing
6) fuel pressure seems fine but I have no way to check
7) have not checked
8) have not checked
9) had it professionally checked 3 years ago, rechecked last month and found one throttle link was too short
10) have not checked but have Gastester to check when appropriate

Other than this fast idle problem, the engine performs very well. I have found a number of issues but none of them have solved the problem. The mouse in the thermostat hose was the cake though. I have no idea who in the Boston area who could do the complete CMA. The few shops I have contacted have shied away. I have not touched the MFI at all.

I think my best proceedure is to check the distributor as per John's previous post since that is easy enough and then remove the throttle bodies and check those. Make sense?

Michael

Michael:

Remember: Any competent Porsche driver tracks faster if brakes come smoothly.

Air filter
compression loss
plugs
dwell
timing
fuel pressure
injectors
belt
correlation
smog

Hey thanks Sherwood. On my engine, the static timing is 0 degrees so I will go with that. So I'll modify my plan from the last post to:

set static timing to 0 degrees as per Sherwood's post

do I then need to test the advance as per John or head straight to the throttle bodies?

Michael

Ok Sherwood, I went out for a drive to warm up the engine. Came home and followed your static timing proceedure. First I marked the distributor position so I could recover and compare to what I had "before".

I tried to use my timing light but it did not seem to be triggered (I verified the rotor was pointing at #1 with the TDC mark aligned with the case mark.) So I pulled the coil wire and used the spark technique. The spark happened about 5 degrees clockwise from my original position mark. I tried to start the engine but it would barely run. So I rotated the distributor about 2 degrees counter clockwise and tried again. This time the engine fired up and sounded good and idle at a hair over 1k. I measured the timing to be about 4 degrees ATC. I tried to get the timing to TC but the idle speed went up to 1500 or so. It seems to be very sensitive to small distrubutor movements. I took the car out for a spirited drive and it continued to idle at 1000+a bit. The engine seemed to pull stronger from idle and a dead stop. It felt pretty good in fact.

So, does this make sense? Do I now need to reset the dwell?

Finally, I tested the microswitch by reving up to 2500RPM. When I pressed the switch, nothing happened. The engine did not slow. I will use my multimeter anf the CMA proceedure for testing this tomorrow. I do not get backfiring whn I take my foot off the gas though so I am a bit confused.

Cheers,
Michael

Michael,
As I mentioned in my last post, using the ignition timing to adjust idle speed is a stop gap measure. While you say you feel adequate power, if you're retarding the timing an appreciable amount (e.g. 4ºATDC instead of TDC), you might be leaving some power on the table.

If you adjust the timing per the factory recommendation (Xº @ 5000 rpm), what are the symptoms? Same high idle as before?

Work on locating that air leak.

Sherwood

Sherwood, Ok. Factory is 30 degrees at 6000rpm. I'll check that tomorrow and see what happens.

cheers,
Michael

If you have a propane torch, turn it on but do not light it. run the tip along the area of the throttle shafts. If there is a leak there, your idle should change. I'm placing my bet on worn shaft bushings...

Well, I did spend a little time this morning checking out the microswitch, etc. Pressing the microswitch button above 2500rpm has no effect but the switch checked out finw with my multimeter. So I went on to check the RPM transducer according to the test in CMA and it is not outputting 12v at 1500rpm or so. I took it off the car and cleaned the terminals but that had no effect. Are there other checks and are these known to go kaput?

Meanwhile, I'll need to wait until later this afternoon to go for a drive to get the engine up to temp to check the timing at 6krpm.

I will also use either the propane or wd40 test on the throttles to check for leaks. I probably need to remove the throttles anyway in order to clean and lube the throttle cross shaft.

cheers,
Michael

Well it rained all day here in the Boston area so I did not have an opportunity to check the timing. But I did do some research on the RPM Transducer - there is a lot of info here! I took the transducer out and opened it up to see if anything looked amiss. One tip: you can remove the aluminum case simply by bending the 2 tabs on 1 side of the case - you don't need to bend all 4 tabs. AND if you bend the 2 tabs that are towards the front of the car (opposite side of the BOSCH black and yellow decal) you can not see those when the unit is installed.

Anyway, the board looked remarkably clean. Several of the components were stabilized with some sort of clear material - it looked original. However, flipping the board over, one of the copper traces - directly in line with the #3 terminal and centered left to right on the board - has about 4 mm of the green coating pealed off 1 mm of exposed copper on each side and about 2mm of what looks like the copper completely corroded away in the center. It looks to be a completely open circuit but I did not have time to test it. I think I should be able to solder a simple copper wire jumper across the gap or would it be better to solder to the posts of components on either side of the gap?

I'll take a photo when I get home tonight.

cheers,
Michael

Ok, here is my disassembly and hopeful repair of the transducer.

removing the case by bending tabs on 1 side only:
http://forums.pelicanparts.com/uploa...1183678212.jpg

component side of board:
http://forums.pelicanparts.com/uploa...1183678389.jpg

back side of board showing missing copper:
http://forums.pelicanparts.com/uploa...1183678553.jpg

new lead soldered across the gap:
http://forums.pelicanparts.com/uploa...1183678699.jpg

installed and ready to test:
http://forums.pelicanparts.com/uploa...1183678851.jpg

Unfortunately, the transducer is still not working properly as tested on terminal 30b (at the microswitch). Even under magnification I could not find anything else wrong on the board. Are there any other vendors that refurbish these units or sell refurbished units? Otto is out until next week.

regards,
Michael

Re the speed switch
Get a mag glass and look at the legs of the transisters
Try lifting them with a small screwdiver you may find the leg looks good, but have rusted away. It's fixable.
Check 12v at A and ground at D in the socket. (I think it's A check diag.)

I would pull the dizzy and clean it, no need to dissasemble, 10 minutes.
Check for air leaks, check advance tube is clear.
Pull off linkages and then replace them watching that each link does not lift your butterflies as you replace it. They should all be sitting on their stops.

If you still have a high idle you have to go one step back and set the butterfly stops as per CMA.

Hey thanks Jeff. I did use a magnifying head set and probed each of the components and they all looked fine. I have not checked power/ground at the transducer socket - I'll do that today. I am building a test harness today so I can test the transducer on the bench while it is still connected to the car - ala EarlySMan. Not sure what you mean by the A and D in the socket? I was going to check for ground at post 3, 12-14v at post 2, distributor pulse at post 4. I already know there is no output at post 1.

I need to check the timing today now that the rain seems to have stopped. We had 2 days of serious downpours - all after work of course. I try not to drive my S in the rain unless I get caught out.

Cheers,
Michael

Michael,
On my 69 E I would set the timing at 4 degrees "after" TDC at idle to get 30 deg at 6000 RPM. The spec for my 69 is 30-32 degrees BTDC at 6000 RPM-no idle setting. I found the above idle setting would give me the spec at 6000 RPM for my distributor. (made checking easier)Your distributor curve may be different. But do not worry about setting it after TDC at idle as long as the timing is correct at 6000 RPM. The timing curves on the early cars are much different than the SC because of more valve overlap on the early cars and more radical cams. For example your valve timing overlap is 5mm vs 1 mm for a CIS SC. Good luck on fixing the RPM transducer.

You could gain some torque at the bottom/midrange by modifying your current advance curve. For example, if you were to limit distributor advance 4º and add it to the static timing (thus, TDC), you'd still have 30º total. And if you were to set it "S" specs at 5ºBTDC, you'd have 9º add'l degrees on the bottom end. This will result in either noticeable bottom end response or borderline detonation, depending on the fuel, altitude, air temp., compression ratio, etc.

Early on, I installed an early S distributor in my 2 liter 911T engine and with some modest jetting/venturi upgrades, never experienced any signs of detonation. Of course, YMMV.

Sherwood
http:members.rennlist.org/911pcars

Are we sure this isn't simply a tired old dizzy? I had mine rebuild recently and it still has trouble coming off advance (big ole valves and cams) but it sounds similar to that...

Not 100% ruled out yet. Right now, the engine is idling at 1000rpm but I have not checked the 6000rpm timing because I have not been able to drive up to temperature the last few days. I am waiting patiently to get home tonight and drive and test!

Plus, now I also know that my RPM Transducer is kaput - so I have that to sort out.

cheers,
Michael

Michael,
This, from the tech section:

"What the heck is this thing called the RPM transducer?

The rpm transducer is used to activate the shut-off solenoid on the MFI pump. It prevents the pump from continuing to pump fuel into the engine when coasting at high speed, which will result in backfiring and other unpleasantness.

The rpm transducer puts out 12v above about 1600 rpm, and 0v below it. It’s connected to the MFI shut-off solenoid through a microswitch that’s activated by the accelerator linkage—the one on the left side of the engine, attached to the input stacks. With your foot off the accelerator, the switch is closed, and if the engine speed is above 1600 rpm, i.e., you’re coasting at speed, then 12v is applied to the relay and it shuts off the pump. If you’re below 1600 rpm, even though the switch is closed, i.e., you’re idling, the solenoid is not activated because the sensor is putting out 0v, and fuel is pumped to the engine.

The transistor leads corrode and break over time. Virtually any generic NPN, like a 2N2222, will work.

Bob Spindel
btindel@gte.net"

---------------------
This shouldn't be an issue at idle speed, yes?

Sherwood

Thanks and you are correct, it should not be an issue. It is one of those sidetrack issues! Originally, I was idling at 1500-1600rpm and someone pointed out that I should be seeing the fluctuations between 1300 and 1500 due to the shutoff circuit described above. Curious, I started testing the microswitch and RPM transducer and discovered the transducer is kaput. Meanwhile, having fixed several other things (i.e. removed a dead mouse from the hose to the thermostat!) and adjusting the static timing, I have been able to get the idle speed down to 1000 but I still have work to do to make sure things are "right".

Cheers,
Michael

Well, in diagnosing the RPM Transducer problem I discovered that the fuse (#2 in the engine compartment box) was blown! I cleaned up the box (that will be my next project - a removal and cleanup) and put in a new fuse. It blows as soon as the engine is started (8amp white body).

How can I daignose the RPM transducer with that fuse blowing? Seems my next step will be to see if the fuse blows with the transducer removed. Need to get some more fuses first.

Any suggestions welcome. Does this point to anything in particular wrong with the RPM transducer?

cheers,
Michael