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Milt,
You dropped a decimal point. CMA says 114 +/- 0.2 mm. 0.1 mm must be the width of a hair!!

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RGruppe #79 '73 Carrera RS spec 2.7 MFI
00 Saab 95 Aero wagon stick
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Old 06-26-2010, 07:45 PM
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The throttle bodies all rest on their stops. The shaft to the pump (114mm) opens the rack slightly. But that isnt my problem. Ive run it with that disconnected.
Ill look deeper into the distributor. It was modified to an electronic version. Perhaps it was messed up, however, the car idled correctly for a good while after that was done. I did put the timing light on it, but I will do it again. It was TDC at low idle. It will idle slowly when I start it as long as I dont give it some throttle. I guess that does give the swing weights a chance to misbehave. That's my target for tomorrow.
Does anyone know someone who repairs or sells RPM transducers?
Old 06-26-2010, 11:27 PM
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Max Sluiter
 
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You do.

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1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
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Old 06-27-2010, 12:48 AM
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Do you have a Pertronix in your distributor? I had a problem with rubbing on the distributor cap, and not allowing the advance to return when you are at idle. I had to "clearance" the epoxy case on the Pertronix by sanding it down with some emory paper.

What I did to trouble shoot it was to wiggle the rotor when idling at 2000 RPM and the RPM would drop. Inside I noticed that it was rubbing on the cap and not allowing the advance plate to return.

May not be this, but something easy to check.
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RGruppe #79 '73 Carrera RS spec 2.7 MFI
00 Saab 95 Aero wagon stick
01 Saab 95 Aero wagon auto
03 Boxster
90 Chevy PU Prerunner....1990
Old 06-27-2010, 12:15 PM
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Porsche Crest

I have adjusted the throttle bodies and run at idle with all the rods disconnected and no change.

This morning, upon cold start up, the car idled at a low rpm for a good ten minutes, I even thought I might have it. During this period I cold run the speed up and it would fall back nicely.
I put the timing light on and followed the distributor advance with speed. It was at 1BTDC at low idle and ran up to the advanced timing marks at speed. When I returned to idle, the advance returned to close to TDC (I couldnt turn the distributor quite to TDC). OK, but it was behaving.
After about ten minutes, just like a monster waking up, it rolled up to 2000 rpm and stayed there.
Using the fuel shut-off solenoid and a hot-wire, I reduced speed to about 100 rpm and let it run back up to 2000, while watching the timing light. I did this several times. The advance seemed to work correctly, as the speed returned to near zero each time the advance returned to near TDC. But when I let loose of the solenoid, it went right back up to 2000. Advance at 2000 was short of the timing marks, maybe 20-25 BTDC. I dont think the problem is the distributor.

Does anyone know who might repair my RPM transducer?
Old 06-27-2010, 12:55 PM
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Otto's, in Venice rebuilds them. 310-399-3221
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Old 06-27-2010, 02:07 PM
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Quote:
Originally Posted by dicklague View Post
Do you have a Pertronix in your distributor? I had a problem with rubbing on the distributor cap, and not allowing the advance to return when you are at idle. I had to "clearance" the epoxy case on the Pertronix by sanding it down with some emory paper.

What I did to trouble shoot it was to wiggle the rotor when idling at 2000 RPM and the RPM would drop. Inside I noticed that it was rubbing on the cap and not allowing the advance plate to return.

May not be this, but something easy to check.
Have you checked the above?
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RGruppe #79 '73 Carrera RS spec 2.7 MFI
00 Saab 95 Aero wagon stick
01 Saab 95 Aero wagon auto
03 Boxster
90 Chevy PU Prerunner....1990
Old 06-27-2010, 02:54 PM
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I have never had my solenoid hooked up on my 73 2.7 MFI motor. It idles at about 950 to 975 with the AFR really working well.

I personally suspect the distributor advance mechanism hanging up. I would be very sure that something like the electronic module, or vacuum advance [if you still have one] causing the problem.
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00 Saab 95 Aero wagon stick
01 Saab 95 Aero wagon auto
03 Boxster
90 Chevy PU Prerunner....1990
Old 06-27-2010, 03:03 PM
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Quote:
Originally Posted by McClellr View Post
Does anyone know who might repair my RPM transducer?
Save yourself $500

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1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-27-2010, 04:17 PM
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$500.00? Wow
It was damaged by a short. Blew the fuse.
Is there an easy method to get to the issue. Just test the transistor?

The name of the electronic ignition is "Perma Tune".
I noticed a chunk out of the plastic on top. Maybe that was an interference, but there seems to be none now. I doint know how the centrifical advance could be the issue after mapping the advance with the strobe this morning. I watched it go from 200rpm and TDC right back up to 2000 rpm several times.

It seems that Im just getting too much fuel. Could the mid-range pump setting be at fault. It is the only thing I havent tried.
Old 06-27-2010, 08:20 PM
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My point was that when the engine is warm the body of the Pertronix on my car would rub on the distributor cap and not allow the advance to drop to what it should be at idle. When I put a timing light on it cold, everything was fine. Drive it of 1/2 hour and the idle would hang at 2000 RPM. If I wiggled the distributor cap in that mode....when it was at 2000 RPM. It would drop down to normal idle.

When warm the advance plate would not return all the way. maybe your Perma Tune capsule is a different shape and this is not the problem.
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00 Saab 95 Aero wagon stick
01 Saab 95 Aero wagon auto
03 Boxster
90 Chevy PU Prerunner....1990
Old 06-27-2010, 09:14 PM
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I checked the timing with the strobe while it was misbehaving and hung on 2000. When I used the fuel shut-off solenoid to force the speed down, the centrifical advance behaved normally. When I released the shut-off, just before killing the engine, 100-200 rpm, the timing was at TDC,but the idle raced back up to 2000.
Old 06-28-2010, 04:56 AM
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Quote:
Originally Posted by McClellr View Post
$500.00? Wow
It was damaged by a short. Blew the fuse.
Is there an easy method to get to the issue. Just test the transistor?

The name of the electronic ignition is "Perma Tune".
I noticed a chunk out of the plastic on top. Maybe that was an interference, but there seems to be none now. I doint know how the centrifical advance could be the issue after mapping the advance with the strobe this morning. I watched it go from 200rpm and TDC right back up to 2000 rpm several times.

It seems that Im just getting too much fuel. Could the mid-range pump setting be at fault. It is the only thing I havent tried.
He's joshing ya as it costs 95 to have it fixed, but I doubt this is your issue.
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Old 06-28-2010, 06:05 AM
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Quote:
Originally Posted by McClellr View Post
I checked the timing with the strobe while it was misbehaving and hung on 2000. When I used the fuel shut-off solenoid to force the speed down, the centrifical advance behaved normally. When I released the shut-off, just before killing the engine, 100-200 rpm, the timing was at TDC,but the idle raced back up to 2000.
OK.....you got that covered. Does not seem to point to the advance mechanism hanging up for some reason.
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00 Saab 95 Aero wagon stick
01 Saab 95 Aero wagon auto
03 Boxster
90 Chevy PU Prerunner....1990
Old 06-28-2010, 06:24 AM
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The rpm transducer has absolutely nothing to do with idle speed. It's only function is to completely shut off fuel delivery upon deceleration at rpm's above idle, and to turn fuel delivery back on at idle. A good number of us don't even run the darn thing.

I'll start with a really, really basic silly question - do you know where the floor throttle is and, if so, do you push it all the way down when the car is warmed up?

Next up the ladder of simple and basic checks would be the air bleed screws. There are six of them, one for each throttle plate. They are on the right side of both banks of throttles, angled back a bit, with springs under them to keep tension on them. These are used to both synchronize idle air flow at all six stacks and to adjust idle speed. It is very common on older, worn out systems to wind up with one of these completely bottomed out. That would be the one on the cylinder with the leakiest throttle shaft or butterfly. The idea is that once airflow is synchronized, these six screws are turned in equally to set idle speed. When the first one bottoms out, the idle is as low as it will ever get. That is often over 1,000 rpm, which really won't hurt anything.

Next up the list are the two rods from the crossbar to the throttle bodies, the ones that connect the crossbar to the throttles at cylinders 2 and 5. If these are too short, they lift the thottles off of their idle stops. Disconnect both of them, and snap one back on its ball. If the throttles move at all, it is the wrong length. Check both sides independantly. Adjust these rods as necessary to achieve zero preload in any dirrection when they are snapped back on. There is a very large tolerance for the length of these rods, both from nominal and compared to one another.

If none of this fixes it, things get a bit tougher. I would suspect the six individual stop screws on each butterfly are missadjusted. The only way to check and correct this condition is to remove the throttles. Each butterfly must be set independantly, with none of the linkage connecting them. They must all close completely, which we check simply by looking through them at a strong light. Adjust the stop screws to take the closing force of the spring off the butterfly without moving it; this is important in that it serves to keep the hard butterflies from rattling against the soft throttle body casting and wearing a groove in them.

Anyway, work your way up through this ladder, from the easiest step to the most difficult. This is all still free, but once we get beyong all of this, it may no longer be. I strongly suspect it's one or the other of the above; if not, we'll go from there.
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Last edited by Jeff Higgins; 06-28-2010 at 09:52 AM..
Old 06-28-2010, 09:50 AM
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Thank you, Jeff.
I have done all the above, including running without any rods attached and it did not change the behavior. The throttle stop screws are all at their minimum while ensuring that the throttle rests on them. It is easy to tell while adjusting them as the sound changes between the butterfly resting on the body or resting on the screw. They are currently at the minimum. I have made many attempts at using the air correction screws to make a difference. It just isnt happoning. I reset them all at two turns off bottom. I checked the pump rod length twice, but also ran with it detached. It doesn't make a difference. I made adjustments to the idle mixture screw behind the fan. It is currently at two complete turns left from full in. Big adjustments made a little or no difference. I have checked the thermostat visually, but dont know how to ensure it isnt keeping the rack open. The one thing that might point to that is that when cold, I idle low. The problem starts when it warms up. Since that is the reverse of the normal function, I dont know how it would act to increase fuel flow with expanded wafers, but the problem does seem to be temperature related somehow.
Although I have a '69, the pump does not have the fuel enrichment solenoid. Although that sends up a red flag, it did operate for some time before the idle problem started.
Old 06-28-2010, 10:55 AM
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Jeff, you had a problem with the barometric compensating cell. Do you think his is bad, causing it to go rich and make the idle higher when combined with the increased airflow from old throttle bodies?

The RPM transducer is not part of your idle problem. I have worn throttles and a high idle when the engine is up to operating temperature. I think it feels smoother that way so I like it the way it is. Maybe the reversion of the S cams with the rattling throttles. Anyway, in some climatic conditions, the idle will creep up from ~1500 to ~2000, at which point the speed switch circuit comes into operation when I am at a stoplight. I get an occilating idle which I sometimes am bugged by. I just increase the revs with the foot throttle, taking the pressure off the microswitch and bypassing the speed switch.

This does not happen all the time. It is sometimes on warmer days, it seems from memory; but there is no real noticable pattern.
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http://www.flickr.com/photos/max_911_fahrer/
Old 06-28-2010, 11:11 AM
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[QUOTE=McClellr;
I took the allen screw out and inserted a screw driver and gently pushed on the shaft. It immediately settled to low idle. I did this several times. If I push far enough, it shuts down. Have I a sticking shaft?
I did the same thing at the front of the pump behind the rubber cover and that shaft seems fine.[/QUOTE]

Buy pushing on the main rack adjusting screw, you are adding more fuel and it seems to like it. "Do not push very hard on this because it might bend the balance bar levers."
You said that you tried to adjust the idle mixture, CW= richer; CCW=leaner, and that did not change anything. I would adjust the main rack 6 clicks CCW and see what happens. I am suggesting this so we can see if a richer fuel mixture will bring the idle down. This might not be the answer, but will help eliminate other possible problems. Buy adjusting the rack 6 clicks CCW will also richen up the complete system. Do you have access to a AFR meter?
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Old 06-28-2010, 11:29 AM
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When my baro cell failed, the plunger came further out, which leans the mixture out. It never affected the idle, though.

Interesting problem. It sounds as though all of the "usual suspects" have been checked, so it may be time to get an O2 meter on it. That may reveal what is going on. Until you do that, you will just be guessing.
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Old 06-28-2010, 12:04 PM
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Today I double checked the heater hose and found a small leak. Fixed that, but no change.
I tried pushing the rack through the front access (again) to see if that was sticking. It feels free and while it decreases speed as I push it in, it snaps back to the same position and speed.
I noticed one thing interesting. My 114mm shaft to the fuel pump is long enough to slightly open the rack when attached. When I pop it off, effectively closing the rack, the speed increases. This sounds like Im running rich at my 2000 rpm idle. I can also increase speed by opening the throttles with the pump disconnected. I might be able to force it down with more fuel but, goodness, what a way to tune an engine. Glad we killed emissions checks in Michigan.
It seems like Im just getting too much fuel. I dont have an A/F meter. I tried leaning the main fuel screw two clicks, with no change, but not richer. I can try that and I can get a meter, but I think I know I am way rich.

Old 06-28-2010, 02:00 PM
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