What causes carb to move to fast idle position? Choke thermostat?

[Freeagle]

The choke thermostat setting is just lining up the notch on the plastic cover to the index mark on the carburetor housing, and then going 1 notch richer. This puts the electric terminal for the choke heater at about the 1:00 position.

Then you put a long vacuum hose on the choke pull-off diaphragm and suck on it to open the choke to the initial clearance. This will determine the fuel mixture when the engine first starts, not the choke thermostat setting. Bend the linkage rod on the diaphragm to achieve a clearance between the top of the choke plate and the carburetor body with a drill bit of 0.140".

Next you lift the fast idle cam until the adjusting screw is resting on the second highest step and measure the clearance between the top of the choke plate and the carburetor body with a drill bit. This should be 0.095". Bend the rod to adjust.

Finally, you set the fast idle speed. This is done with the engine fully warmed up, the EGR vacuum hose disconnected and plugged, and the fast idle cam set to the second step. Adjust the screw to achieve 1850 RPM in neutral.

It also has what is called a sole-vac throttle positioner on the carburetor that kicks up the idle speed when the engine is cold. The electric part kicks up the idle speed up to 800 RPM in gear when the ECU is in open loop (coolant temp under 135 degrees F) and the vacuum part kicks the idle speed up even higher to 900 RPM if the air cleaner is under 55 degrees F.  Those things are helpful to have because the choke opens quickly (before the engine is fully warmed up) and the higher idle speed from the sole-vac can keep it from idling too low or stalling during that interim period.

A properly functioning and adjusted choke along with sole-vac system will start very quickly in cold weather and rev up to ~2000 RPM within a few seconds. You then tap the throttle to drop it down to ~1200 RPM, put it in gear, and drive away. The choke opens quickly, so it'll drop off the fast idle cam within a couple minutes, probably before the engine temperature gauge even starts to move. Then it'll be just the sole-vac holding it at 800-900 rpm in gear. The sole-vac will release the throttle down to 600 rpm curb idle only after the engine and the air cleaner are warm enough.

[86Woodgrain]

The choke thermostat setting is just lining up the notch on the plastic cover to the index mark on the carburetor housing, and then going 1 notch richer. This puts the electric terminal for the choke heater at about the 1:00 position.

I can confirm that using the notch on the thermostat housing is not an option anymore on mine at least. Perhaps the spring is not as strong as it once was? I have to ignore the mark on the thermostat to set it correctly it seems now.

I have set my choke initial setting, pull-off, and fast idle correctly using the specs in the carb rebuild sheet / underwood decal. In tinkering with it I did alter the fast idle screw setting, which I will correct in the coming days when I know if the thermostat is actually opening/closing when it should. The fast idle is very close right now anyway.

It also has what is called a sole-vac throttle positioner on the carburetor that kicks up the idle speed when the engine is cold. The electric part kicks up the idle speed up to 800 RPM in gear when the ECU is in open loop (coolant temp under 135 degrees F) and the vacuum part kicks the idle speed up even higher to 900 RPM if the air cleaner is under 55 degrees F.  Those things are helpful to have because the choke opens quickly (before the engine is fully warmed up) and the higher idle speed from the sole-vac can keep it from idling too low or stalling during that interim period.

A properly functioning and adjusted choke along with sole-vac system will start very quickly in cold weather and rev up to ~2000 RPM within a few seconds. You then tap the throttle to drop it down to ~1200 RPM, put it in gear, and drive away. The choke opens quickly, so it'll drop off the fast idle cam within a couple minutes, probably before the engine temperature gauge even starts to move. Then it'll be just the sole-vac holding it at 800-900 rpm in gear. The sole-vac will release the throttle down to 600 rpm curb idle only after the engine and the air cleaner are warm enough.

This is the first time I've heard of the sole-vac being used during warmup, does that apply to 1986 models? To my knowledge Sol-Vac was only used to bump up idle for A/C or rear defrost usage. My Sole-Vac has been unplugged for 2 years and I'm sure was non-functioning before that.

[MIPS]

Sol-Vac is also operated by the computer through the Idle Control Relay (for the solenoid half). On a hot start the computer will engage the sol-vac for 15-45 seconds to allow the charcoal canister to purge and force fresh gas into the lines to purge any vapor. When the engine is cold it will also operate the sol-vac at a high idle to accelerate warmup, then release and back off the timing once the CTS and TAC are satisfied.

In all the Sol-vac provides TWO different high idle positions. One from the vacuum kick which is also computer controlled and one from the solenoid which is computer AND accessory controlled. When you adjust any of the idle screws they have to be done in sequence as per the TSM because one affects the other.

As I discovered a few months ago if the computer sees the RPM's fall too low or become inconsistently low (from say a bad TACH- connection) it will also engage the sol-vac to hold the idle above curb RPM until the signal it receives settles down because it thinks you are about to stall.

[86Woodgrain]

I learned something new today. Well the proper setting of the sole-vac looked complex so I left it alone (unplugged) when I rebuilt the carb. I need to fix that.

[AMC of Houston]

Setting the Sol-Vac is also part of the IS-12e Service Letter procedures.  Want a copy?

[86Woodgrain]

Setting the Sol-Vac is also part of the IS-12e Service Letter procedures.  Want a copy?

No I'm sure I have a copy somewhere. I followed all the directions for setting timing, idle, etc when I rebuilt the carb 2 years ago. I figured the Sole-Vac was not needed so I left it unplugged. The procedure seems complicated for setting it correctly. I guess I could try just plugging it back?? Roll the dice? Or not?

[MIPS]

Plug it back in. The worst you get is it's stuck on all the time because something else is wrong.

[86Woodgrain]

Plug it back in. The worst you get is it's stuck on all the time because something else is wrong.

I replaced all vacuum lines, made sure they were going to the right place. Replaced the temp sensor in the air cleaner (that was very difficult to find NOS part with correct temp rating), replaced the vacuum temp air switch thing in the manifold under the carb, etc. I have done everything I can to get the car as close to 100% factory fresh as possible in terms of configuration, except my brain over the Sole-Vac theory of operation.

I am quite confident nothing else is wrong. I even fixed the EGR and it is operational.

As an aside, what a mish-mash of electronics and mechanical stuff eh? This awkward stage between straight up simple carb and fuel injection. I know I'm close to getting it correct again. Between the choke thermostat and the Sole-Vac I will hopefully be set soon.

The manual choke kit that I bought arrived this morn. I'm going to leave it sealed in the box with the hopes that I don't actually need it so I can return it. Fingers crossed LOL

[86Woodgrain]

Setting the Sol-Vac is also part of the IS-12e Service Letter procedures.  Want a copy?

FYI no need to email it to people, it’s available online @ http://amceaglesden.com/guide/November_1987_-_IS_12E_-_Idle_Speed

[86Woodgrain]

OK next day update. A little colder today, -7C or 19F.

I connected the SoleVac vacuum line and electrical connector. Pressed gas, choke snapped closed just like it should, car went to fast idle cam. Let it warm up for 5 mins, it came off fast idle.

Went for a ~15 min drive, came back the throttle cam thing is back to normal spot (not fast idle which I knew) and again the choke plate is not open fully yet, it opened maybe 1/3 of the way (see pic below).

I'm hoping to get the engine fully warmed up later today to check the choke plate to see if it fully opens. Also, I'd like to re-set the fast idle speed and stuff. I'm quite sure the current fast idle speed is too slow but that's easy to fix.

I can't actually tell if the SoleVac did anything in my short drive today. When I came back I tried turning on the headlights and the rear defrost and the RPM didn't change. So yeah.

I think I'm on the right track, but I also think I need to turn the choke thermostat back a notch (leaner) and try again tomorrow. I don't think the choke plate is opening up quickly enough that's why I think I need to turn it leaner provided it still fully closes when cold.

[MIPS]

It's -7 here right now as well and the car has been sitting all day so I can replicate the results when I drive home in two hours.

Edited: Because the Carter 2-barrels are so similar to eachother in how they are adjusted, I have in the past used a Mopar training video to assist in how the feedback 2bbd's are also adjusted. Among the things that are similar are choke and fast idle adjustments, though they don't use an electric thermostat to open the choke.

https://www.youtube.com/watch?v=nBtqTbGu2eU

[86Woodgrain]

MIPS, I'll watch that video tonight.

Alrighty... update time again...

The choke plate was fully open after my longer 20-30 min drive, so I'm not worried about that for now. I did move the thermostat ~2mm to the lean side for tomorrow morning test purposes (to see if the choke opens faster after cold startup).

I hooked up a tach tool, set the fast idle to 1750 rpm (firewall decal says 1850 +/-100 so I'm good) with EGR line plugged.

I set the curb idle with solvac disconnected to ~590 rpm (spec is 600 rpm +/-50)

I tried to set the SolVac but it did not hold vacuum. Went to my parts car, grabbed that one, it did hold vacuum. So I hooked it up and set the vacuum SolVac high idle to 750 rpm (spec is 800 rpm +/- 50).

BUT... I could not get the electrical side of it set for the life of me. I put 12V from battery to the unit and it wouldn't extend. I tried opening the throttle to let it extend and it just wouldn't.

So I almost had it guys. I'm not sure if I did something wrong or if part of the SolVac could be broken? Honestly I felt the instructions for that step was a little unclear.

When I turned the car back on when I was done, everything hooked up right, the car went to the increased idle for 60 seconds (I timed it), so that must have been for the EVAP purge. It did it again when I got home I restarted, same thing.

I turned on the headlights, no RPM change. I turned on the rear defrost, no RPM change. So the 12V bump from the SolVac doesn't work but I think the rest of it is fairly well sorted now. Eventually I will need to fix that but I guess it's not really too urgent.

As an aside, after the car sits overnight I have to pump the pedal quite a few times while cranking for it to fire up. I'm not super worried yet about that, once I get the choke and SolVac fixed I may research that. When I rebuilt the carb 2 years ago I would only need one or two pumps in the cold for it to fire. Who knows, after setting the speeds today that may help in the morning!! Fingers crossed. I feel like I'm making progress though.

I recorded today's startup, listen for how many times I pump it - https://youtu.be/71mYMJqy59g - the fast idle was WAY too low so that will be fixed with tomorrow's cold startup.

[MIPS]

Verify continuity or a low resistance between the Sol-vac wire and the metal bracket used to attach it to the carb. If there is no continuity either the wire or the solenoid is open. Also if you do not have a good ground between the carb and the manifold that will in theory cause the sol-vac AND the thermostat to not work properly. Some of the aftermarket kits include a ground strap but normally the four bolts holding the carb down should be enough.

For cold starting I've never needed more than one pump, even in -30. Here's another handy (thought probably really obvious) Mopar video - https://www.youtube.com/watch?v=8wZvZgYCG7Q

If you were closer here in central British Columbia you would be more than welcome to drop in and I could spend some time looking over the carb and adjustments. I've done it enough myself I got no issues dialing it in for someone else having trouble.

[86Woodgrain]

I edited my post above FYI in case you didn't see it all.

Good idea, I will check for continuity. I know the Sole-Vac from the parts Eagle was pretty dirty and I didn't clean it up before putting it on.

[86Woodgrain]

Is there a document from the TSM or elsewhere that outlines all the conditions when the SolVac operates? I looked in Eaglopedia that is my usual go-to source but didn't see full theory of operation.