Cold dogs, hot wife and Subaru mystery

My 1984 Subaru GL wagon almost didn’t start yesterday, temporarily stranding my 3 dogs, wife and me at a relatively remote location in Southwest Montana. The car has been starting an running well all summer, yesterday I loaded dogs and wife into vehicle and motored to a building with water and power, but no phone service and wood heat only. The car sat in a fairly brisk wind (20 mph) at roughly 32 degrees F for 4 hours. Went out to start and it cranked briskly, but no hint of ignition. Plugged the block heater in for about 90 minutes after wrapping the hood in some tarps. Cranked it over using normal starting procedure (no pressure on gas, clutch depressed) and no joy. Check fuel in underhood filter, no problem. Finally, tried cranking with gas pedal fully depressed, and car reluctantly started and would run very roughly at about 300 rpm for 15 to 30 seconds with pedal floored. After about 10 of these starts, car would run with less depression on pedal. Tried starting in normal fashion and car ran normally. Drove home without problem. Car is an 1800 cc, overhead valve, pushrod, normally aspirated, Hitachi carburated 4WD wagon with 84000 miles. Only known problem is oil leak from oil pressure sender, replacement is on order. I’m guessing that the problem is a failed temperature sensor somewhere in either the feedback carburation spaghetti or connected to the ECM. Any suggestions would be welcome, my wife has taken to looking at car ads.

I would suspect a carburetor problem, possibly with the choke. It may be time for a carburetor rebuild or a new carb.

I can reproduce the problem by pushing the car out of the garage and letting it sit outdoors for a couple of hours when the temperature is below 35 degrees. Pushing it back in the garage and letting it sit for a couple of hours at roughly 50 degrees and the starting problem is gone. So 10 feet of distance and 15 degrees are the only two variables. Both the garage and drive are level.

I assume the electric choke on the carburetor is governed by temperature. I’d focus on the choke circuit. If it’s not working, it could allow the engine to start normally at higher temps but prevent it from starting normally at low temps.

As a first step, you could take off the air cleaner and look at the carb to see if the choke is engaging at low temps. If the choke isn’t engaging regardless of temp, something is wrong.

Here are some diagrams that might help you with the choke:

I think you’re overthinking the problem a bit. Make sure when the engine is cold that the choke flap is completely closed but operates freely with the touch of a finger.
As to ragged running upon startup, that could be due to a failed choke pull-off diaphragm. That is the vacuum pod near the top of the carburetor that is designed to open the choke slightly during a cold engine start. It has a rubber diaphragm so it wouldn’t surprise me that given the age of the car the rubber has decided to go south.

Also check the choke flap and the inside of the air cleaner for heavy sooting as that can affect carburetor/choke operation. Any heavy sooting could be due to a faulty ASV, or Air Suction Valve.

From the tone of your post, I take it you were at altitude. How high was the Subaru for this start?

It sounds like the carburetor was not compensating for the thinner air at altitude. The choke would definitely have been over choking. When you put the accelerator pedal to the floor, you did a ‘choke clear’ but as soon as you got it running the mixture was still too rich. Once the choke element got warm enough to release the choke, it would run better.

This engine does not have a O2 sensor and the ECM connor go into closed loop. The emisssions system does have an altitude compensator that adjusts the mixture through the air bleeds on the main and idle passages. As you may have already seen the emissions system is a spagetti factory of hoses. So go over all the lines and make sure that there are no split or weak hoses of the system. I don’t know what the procedure would be to check the calibration of the altitude compensator. Between the carburator and the emission control system this might be a bear to trouble shoot.

Hope this helps. Good luck on this.

You might want to consider a new(er) car, 30-year-old vehicles will have problems. Or use it around town, but have something more reliable for trips into the boonies.