Fast Idle and Idle Vacuum Setting on Solex

[tomking]

I was working on the "new" Manta today trying to get it to idle smoothly. When reading the 73 factory service manual about fast idle settings it said to set the fast idle lever to a 3200 RPM idle?? Tell me that is wrong!! I dont believe that is correct. I set it to about 1700 instead.
Plus I have another question. In carb and throttle linkage section of FSM, under Basic Idle Adjustment section it says to adjust the throttle valve stop screw to get 6 inches of water vacuum at the port for the vacuum advance. While I dont have a manometer I do have a vacuum gauge and isnt 6 inches of water the equivalent of 11.2 mm of Hg? Isnt that a helluva lot of vacuum for that port at idle? What am I missing? I admit I am learning but question that also. Thanks for your help.

[baz]

also remember as some one once said grass hopper

95% of carb problems are ignition problems

[tomking]

Baz I have been thru the ignition. PO had put on a Delta Mark X Cap Dis system. I assumed this came with some breakerless system but in doing a search it appears that some continued to use the points. I dont know if I have points or what yet, will check tomorrow. But except for that, all ignition parts are new.
My question is whether or not those two bits of FSM information are correct? I dont think the fast idle speed is and I question the accuracy of putting 11 mm Hg on the advance at idle??
PS, you've got me thinking though, Baz. When I checked the dwell it was only 35 degrees, not 50. So maybe it has points and they need adjusted? I will check them tomorrow. Thanks.

[Bill Hoffmann]

Originally Posted by tomking In carb and throttle linkage section of FSM, under Basic Idle Adjustment section it says to adjust the throttle valve stop screw to get 6 inches of water vacuum at the port for the vacuum advance. While I dont have a manometer I do have a vacuum gauge and isnt 6 inches of water the equivalent of 11.2 mm of Hg? Isnt that a helluva lot of vacuum for that port at idle? What am I missing? I admit I am learning but question that also. Thanks for your help.

That 6" measurement is 3" up and 3" down on a closed tube manometer. While that might seem like a lot, it's hard to read that much vacuum on most standard gauges. You will see the needle move though. That's an important setting and will affect drivability. Set correctly, and it brings in vacuum advance as the throttle is opened. If the throttle stop screw is open too much, you get an erratic idle and don't have the advance when you need it.

Bill

[timemachine]

Tom,

It doesn't sound like ignition even comes into this, you're just setting idle speeds.

I'm familiar with the fast idle spec from the time these cars were new (okay, I'm an old guy). While it seems excessive, the numbers are correct to spec. The practice involved pushing the pedal to the floor, releasing it and starting the car with no pedal, at which point you'd a) run back into the house until it warmed up or b) take your broom to the foot of snow on the hood and a pickax to the ice on the windows. (That's providing you got your door open to start with, do they still make Lock-Eze?) I always figured the first seconds of running were toughest on a cold engine, so I'd start it normally and nurse it around 2K for a minute or two to get the oil flowing in the head before turning it off and setting the choke for a cold start and repeating a) or b). Never seemed to hurt a thing though it did make a racket common to cars of the time. Newer engines operate similarly, but are quieter and step off fast idle quicker and automatically.

It all depends on conditions where you live. If you live in San Diego you may never meet your fast idle. But, a lot of people think it's better to warm a cold engine at higher RPMs than to drive it under load before warmed up, and a COLD CIH engine can take 15 minutes or more to get to operating temp. That's more than most commuters build into their morning schedule, hence the factory setting. Since it looks like it will never snow again on the east coast, I have dialed mine down a bit. The FSM says 3200-3300 fast idle, the Haynes manual says 2700, (though there's no particular reason to trust them). I don't beat up this car to keep my job like I did with the old ones though, so if you're in the same boat I'd adjust accordingly.

Jim

[tomking]

That 6" measurement is 3" up and 3" down on a closed tube manometer. While that might seem like a lot, it's hard to read that much vacuum on most standard gauges. You will see the needle move though.
Bill, if you barely see the gauge move on a standard vacuum gauge then I have incorrectly converted the 6 inches of water to mm Hg. I converted it to 11.2 mm of Hg which shows BIG time on a vacuum gauge. What reading in mm Hg is correct?

[hrcollinsjr]

Originally Posted by tomking When I checked the dwell it was only 35 degrees, not 50. So maybe it has points and they need adjusted? I will check them tomorrow. Thanks.

If you do have points get them adjusted correctly first! The fast idle setting rpm's is for a warm engine. Warm the engine up, shut it down, set the carb throttle on the fast idle step, and start the engine without using the gas pedal. This is how you arrive at the correct setting. When the engine is cold it won't idle this high, at least mine never have. I believe it is hard on the engines to start them and leave them at the highest fast idle setting and go back into the house until the engine is warm. As soon as the engine starts warming up the idle speed increases until it is idling at +/- 3000rpm with no load. More modern cars automatically slow the idle down as the engine warms up.

Tom, I usually set my fast idle speed at 2700 rpm and never had any problems in cold weather and I would assume our conditions are similar, I'm in middle TN.

Harold

[Bill Hoffmann]

Originally Posted by tomking Bill, if you barely see the gauge move on a standard vacuum gauge then I have incorrectly converted the 6 inches of water to mm Hg. I converted it to 11.2 mm of Hg which shows BIG time on a vacuum gauge. What reading in mm Hg is correct?

I think your conversion may be correct, but most gauges read inches of mercury, not mm. 11.2 inches would be way too much vacuum, but 11.2 mm sounds about right.

I checked the tune-up specifications. The beginning of vacuum advance should be at 2.9 to 4.1 in Hg. That will depend on the vacuum canister itself, but it tells us the range it's supposed start, and naturally you would want to be below that with the throttle closed.

A quick check I do to see if the throttle stop screw is set correctly is putting a vacuum gauge on the advance port. As I said, the needle should move a little, but barely get on the readable part of the scale (an inch of Hg or less).

Bill

[gr_diver]

First of all verify and correct your dwell, and after it is correct at 50=-3 degrees time the engine, as initial timing affects idle speed settings.

Then set the throttle stop screw for one of the following values:

1-15 mm Hg
or
0.1 - 0.6 in Hg
or
20 - 200 mm H2O
or
0.8 - 8 in H2O.

Then set your idle speed according to your transmission, as per FSM.


About the fast idle speed the 3200-3300rpm value is correct, and thus it should be set, because this is set with the throttle actuating spindle at the top step of the step cam (see pic). In real life though, when starting the engine the choke valve will be fully closed, but the moment it starts running on it's own the engine's vacuum will pull the choke valve a crack open, and then the spindle will rest on the second step. Just like how the by-pass cable feeds 12V during cranking, and then it gets disconnected and the coil gets power from the ballast resistor.

For a hot engine the second step of the cam brings the fast idle at about 2500rpms, but with the engine cold (as when the choke operates) it would idle at about 2000rpm...

HTH

[2 Fast 4 U]

Originally Posted by tomking I was working on the "new" Manta today trying to get it to idle smoothly. When reading the 73 factory service manual about fast idle settings it said to set the fast idle lever to a 3200 RPM idle?? Tell me that is wrong!! I dont believe that is correct. I set it to about 1700 instead.

Actualy it's not wrong, you should set the fast idle when the engine is cold, and the choke is working, my FSM says to set it at 2700 RPM idle [A Ascona 1.9 S]

Originally Posted by tomking Plus I have another question. In carb and throttle linkage section of FSM, under Basic Idle Adjustment section it says to adjust the throttle valve stop screw to get 6 inches of water vacuum at the port for the vacuum advance. While I dont have a manometer I do have a vacuum gauge and isnt 6 inches of water the equivalent of 11.2 mm of Hg? Isnt that a helluva lot of vacuum for that port at idle? What am I missing? I admit I am learning but question that also. Thanks for your help.

A brief workshop in physics:
1 meter = 1000 milli meter <-> 1 m H2O [water] = 1000 mm H2O
1 m H2O = 1 bar
1 bar = 1000 mbar [milli bar]
1000 mm H2O = 1000 mbar
1" = 25.4 mm <-> 1" H2O = 25.4 mm H2O = 25.4 mbar
1 mbar = 0.02953" Hg = 0.75 mm H2O
so if we calculate right 6"H2O should be:
6 x 25.4 = 152.4 mbar
152.4 mbar = 152.4 x 0.02953 = 4.5" Hg
or 152.4 x 0.75 = 114.3 mm Hg

so 6" H2O = 114.3 mm Hg
Hope this helps you

[2 Fast 4 U]

Originally Posted by gr_diver First of all verify and correct your dwell, and after it is correct at 50=-3 degrees

Correct dwell setting is 50º ± 3º

[tomking]

Well I turned 60 3 days ago and it is time to begin wearing reading glasses. I looked again at my vacuum gauge and I was using the wrong scale. I hate working with glasses on when the weather is warm to hot. In the 50s it is ok.
I did pull the dizzy and I have an old Allison ignition system driving the Mark Ten Cap Dis system. I had an Allison on one of my GTs and I could not get rid of a miss. Finally I removed the allison and installed points and the miss was gone. So I converted it to Pertronix. I suspect this Allison may be faulty too. For those who know, can I use the Pertronix to drive the capacitive discharge system too?
My dwell is 35 degrees and that is fixed by the Allison. Could this be the wrong Allison? Or are Allisons adjustable? Thanks.

[Bill Hoffmann]

Originally Posted by 2 Fast 4 U so 6" H2O = 114.3 mm Hg

That might be correct for barometric pressure, but the FSM method describes something different. The manometer they show is really an open-tube type with valves on top of each tube. You are supposed to first open both tubes to equalize the levels in the tubes, which also zeroes the instrument for the surrounding atmospheric pressure. It doesn't actually say this, but you then close both valves to the atmosphere before connecting the hose to the vacuum port. If you did not close the valve on the suction side, nothing would happen, and if you don't close the other side, the water would be sucked into the vacuum port. Anyway, the resulting displacement of water is measured. I honestly don't know the conversion factor to go from inches of mercury to inches of water in this type of closed-tube manometer.

Thanks to gr diver for supplying the English and metric equivalents. From those specs you can see that we are dealing with pressures too small for common gauges to measure accurately, but if you don't want to bother with the manometer, it seems as long as you keep the vacuum at the advance port below 0.6 in Hg you are OK. As I said, I just look for movement of the gauge but make sure it's less than 1.

Bill

[tomking]

That is what I tuned it to Bill, just a little movement on the gauge. Thanks guys.

[gr_diver]

Bill, don't mention it for the vacuum values, glad I can help anybody!

For throttle stop screw adjustment, I used a clear plastic tube formed in a U on a piece of wood. I sank one free end in a glass filled with water, and sucked on the other side until 8 inches of the tube were filled with bubble free water. I let it equalize (both sides of the U had 4 inches of water), then drew a scale on the wood block, and then using a tee I connected one end to another piece of plactic tubing, long enough to have the device hanging from below the hood and the end reaching the carb. With both ends opened, I connected the long end to the carb, idled the engine and adjusted for 3 inches down/up in each side of the "U" respectively. Never touched the throttle stop screw again, and still reads the same after 3 years...

This way the vacuum canister actuates the moment you open the throttle (verified), without advancing at all during idle, and possibly messing the static timing value.

I then also verified that the carb's acceleration pump starts dripping fuel also the moment the vacuum canister kicks in, and this provided the best off-the-line acceleration ever, for my car at least.

Hope these are helpful...

[David McCollam]

Tom,

According to my friend Uwe, the Opel is especially sensitive to the 50 degree dwell angle. The Pertronix should come in at about 48-50. I'd try that and see if I got a better result on the idle.

Dave