By on March 3, 2013


As long as it’s still the winter season in the Northern Hemisphere—more wintry for some than others, here in the U.S.—it seems appropriate to stay on that topic for a while longer, here on the “Memoirs” page.

Having spent much of my career as an auto tech and shop owner in the Southern California area, I really didn’t get much of an opportunity to solve cold-weather problems on customer vehicles—mainly because there just wasn’t (and still isn’t) much of that stuff going around, down there.

Moving to New York—and then Louisiana—in the ‘80’s quickly changed all of that.

Of course, most vehicles had carburetors back then; and compared to those equipped with fuel injection, they tended to be more susceptible to the cold—especially when accompanied by high-humidity conditions (of which there is no shortage in either locale).

This fact led to a number of personal cause-and-effect revelations, which, while unfamiliar to me, undoubtedly were familiar ones to the locals. They were interesting revelations, nonetheless; and I’m going to relate a couple of the highlights right now.

When it came to choke systems on most typical carburetors of the day, I found that choke setting was not terribly critical in SoCal, as long as the plate was fully open when the engine was warm. Yes, setting did become a bit more critical on “emissions” carburetors—and British vehicles always had to have a fully functional choke (technically referred to as “cold-start enrichment”), even on the typical Los Angeles “cold” start.

But drop the temperature down to anywhere at or below freezing, and any flaw—however subtle it may have been—made its presence known in no uncertain terms. Choke plate not closing enough? You might have to pump the living daylights out of the accelerator pedal just to get the engine fired and keep it running long enough to warm up, and run without stalling at idle. Choke vacuum break not operating (with a properly adjusted choke plate)? Sure, the engine would start right up, only to be shortly followed by pronounced “chugging” and massive amounts of black smoke out the tailpipe. On later “emissions” engines, the thermo-vacuum valves controlling this process would fail and cause the same sort of conditions. I personally owned a Honda Accord that experienced that problem. On GM cars of the day, even a “no-charge” alternator condition would cut power to the choke heater coil, and the choke would fail to open quickly and completely.

Unlike the “repair wiggle room” prevailing atmospheric conditions in the Southwest afforded, attempting some kind of witty bypass maneuver in true winter climes got you into more of a mess than biting the bullet and just making the O.E. system function by the book.

Another problem I ran across—especially during the winter in Louisiana—was a malfunctioning intake air control system wreaking havoc with vehicle driveability.

The customer would claim that they’d be motoring along without a problem—often at a steady state highway cruise—and the engine would lose power, and eventually sputter and shut off! If they’d let it sit for a few minutes, they could restart without problem, and resume cruise for about five to ten minutes before experiencing the power loss and stall all over again.

Now in Los Angeles, the only problem I had experienced with TAC (Thermostatic Air Control) on carbureted engines, was when the air door would stay closed off to cold air, and engine “ping” followed by “vaporlock” when returning to idle would ensue, due to excessive heat in the intake air. Yes, that problem would also occur—probably even more acutely—in the Deep South. Usually, the quick and temporary solution to that problem was to make sure that the air door stayed open to cold air only; without much concern for any consequence involving the need for hot air, at any point.

The strategy worked in the City of Lost Angels, but not in the State of LA. At least not for year-round vehicle use!

What would happen during the winter, if the TAC system was not providing enough heated air to the carb vis-à-vis the air filter housing, was the formation of ice around the throttle plate. If the ice buildup got heavy enough, it would literally shut off the engine! In the state of LA, it didn’t have to be really cold for this to happen, either. It could get so damp down there, ambient temperature only needed to drop to around 50F for that to happen!

The customer would always be surprised when they learned that this was the sole cause of the problem!

Stay tuned for more “revelations”, next week.

Phil ran a successful independent repair shop on the West Coast for close to 20 years, working over a decade before that at both dealer and independent repair shops. He is presently semi-retired from the business of auto repair, but still keeps his hand in things as a consultant and in his personal garage.

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14 Comments on “MEMOIRS OF AN INDEPENDENT REPAIR SHOP OWNER: Cold-Weather Cause-And-Effect (not “Tall Winter Tales”) ...”

  • avatar

    It is not the throttle plate that ices up it is the venturi(s) which then cuts off the flow of fuel.

    • 0 avatar
      Phil Coconis

      Sure, it all starts in the venturi (see photo), but eventually it spreads to nearby component parts of the carb (like the throttle plate). Experienced this frequently with Honda products of the day; as I worked @ the sDealer in Lafayette then…

      • 0 avatar

        It is the venturi(s)icing over that causes the engine to die as that is what shuts off the fuel flow. I’ve seen it many times as the conditions in my area frequently are perfect for causing carb icing.

      • 0 avatar

        Yes, the air expanding inside the venturi causes it to cool somewhat, but the major pressure drop is not across the venturi, but the throttle plate itself. So even without a venturi, there is still a possibility of icing of the throttle plate. This is why most fuel-injected cars use engine coolant to heat the throttle body. I’m not familiar with the newest cars – do they still use coolant or do they use electric heaters?

      • 0 avatar

        Scout-Dude: no doubt you may able to see ice at the venturi. Are you suggesting that the passage at the venturi is totally clogged with ice?

        Squirt some carburetor cleaner into the main jet in the fuel bowl while looking down the throat of the carb and look where the carb cleaner comes out.

        My guess is that eventually the formation of ice will block the discharge tube from the main jet. The main jet discharge tube protrudes into the center of the venturi or a little below.

        Even before the main jet is blocked even a thin layer of ice at the venturi will result in an increased air velocity at the main jet discharge tube – which will cause the carburetor to run hog rich. Hence, a smokey exhaust.

        Add in the turbulence from any ice on the throttle plate and one should be pulling over to the side of the road before ice blocks the discharge tube for the main jet in the center of the venturi.

  • avatar

    I always enjoy your musings Mr. Schmitt .


  • avatar

    Phil – the solution on an old American straight six was to cast the intake and exhaust manifolds as a single piece. At start up on a cold morning most older engine ran pretty rich from the needed choke or enrichment circuit.

    The combined intake and exhaust manifolds doesn’t fly with cross flow heads. So, to provide manifold heat, some intakes had a passage plumbed to the heater hose. Pierce Manifolds used to sell such an intake manifold that worked well with a two barrel Weber. The hot water passing through the intake warmed up the carb a good bit on a cold day, provided that you were using the heater.

    It’s not just icing of the carb that is a problem, carbureted engines with long intake runs need to be heated just keep the fuel vaporized.

    Upon start up for the first time of the day, the engine is not much of a heat source, hence the heated air duct from the exhaust was used to cut emissions by keeping the fuel atomized until the engine warmed up. A thermostatic device was used to shut off the heated air duct, once the engine was at operating temperature.

  • avatar

    Ah, the days of carburetors, when you learned to keep a can of starting fluid handy for these times. Pull off the air cleaner, give it a good shot straight down the bore and stand back as someone tried to turn it over, enjoying the 16 inch fireball that often resulted. I still have a can of starting fluid (ether) around for euthanizing injured small animals found in my yard.

    • 0 avatar

      Use a 78′ Chevy for my daily driver. Keep a can under the bench seat. Don’t need it often, but once every several months it just doesn’t want to start.

  • avatar

    “On GM cars of the day, even a “no-charge” alternator condition would cut power to the choke heater coil, and the choke would fail to open quickly and completely.”

    Choke heater coil ?. Dang that’s getting high tech !. My old 71 Buick just had a bi-metal coil spring on top of the intake manifold with a control rod running up to carb. Rochester 2-barrel, rebuilt it myself without having ever done something like that before just by going off the parts diagram from the NAPA rebuild kit. Never had any cold weather driving problems, except for the secondary vacuum choke pull-off crapping out twice.

    • 0 avatar

      On GM cars, the electric choke coil heater was a major improvement over the engine-heated ones in most cases (they wouldn’t heat up enough – I had several 1960s-70s GM cars with this problem).

      But you couldn’t just connect the electric choke heater power directly to the ignition wire, as one could just sit in the car with the ignition on and the engine not running and the choke would heat up – not good.

      So, ingenious engineers used power directly from the alternator, upstream of the rectifier diodes, such that no power was provided to the choke heater unless the engine (and alternator) was actually running – this way, the warmup profile of the choke heater would match the engine warmup.

      So when the alternator was not functioning for some reason, it was not uncommon for the choke to stay fully on, causing massive black smoke out the back.

  • avatar

    My Chevette pulled that trick on me across the state of Illinois once. The vacuum switch that triggered the warm airflow over the exhaust manifold failed. The resulting temps had me pulling over at every rest area and using the hand dryers in the bathroom to thaw my air filter. The warmth of the engine thawed the carb and I’d head out again, only to be 35-45mph top speed by the next rest area.

    I was on the road and focused on getting home. Knowing what happened now, it would have been a simple procedure to reroute the vacuum lines bypassing that switch and making it home with no drama.

    • 0 avatar

      Yes, in cold weather, there would be no problem with routing full manifold vacuum to the dashpot on the air cleaner intake snorkel such that fully heated intake air via the exhaust manifold would have been used.

      I knew one or two people who used to connect theirs in exactly that manner, for winter months, and then just disconnect it in the summertime.

  • avatar

    I solved this on my ’81 Eagle daily driver by installing a manual choke cable. SOOOO much more reliable!

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