Why Carbureted Cars Are Hard to Start When Cold

[paulo57509]

Originally Posted By: parimento1
I always wondered why this was the case. My father's 78 Ford LTD and uncles 84 Cutlass would be major pains to start in winter. FI cars start right up no matter what the temp - why is that?


IMO, for those model years, carbs were calibrated ridiculously lean, even when on the choke.

 

[lexus114]

My favorite sound from a carb,was the good ole Rochester 4bbl.

Ya just cant beat that sweet sound!

 

[paulo57509]

Originally Posted By: lexus114
My favorite sound from a carb,was the good ole Rochester 4bbl.

Ya just cant beat that sweet sound!


You haven't heard the sound of a WOT Tri-Power equipped Pontiac/Chevy/Olds, have you.

 

[lexus114]

No,never got to hear one of those. But a good ole oldsmobile rocket 350,(with the air cleaner lid turned up side down.)

 

[Kestas]

Originally Posted By: parimento1
My father's 78 Ford LTD and uncles 84 Cutlass would be major pains to start in winter.

I had an 82 Omni 1.7L that started up easily even in the coldest days of winter. (Yes, this was the VW engine).

 

[01rangerxl]

Originally Posted By: CivicFan
FI is just more unnecessary electronic mumbo-jumbo. They need to get rid of these and go back to the good old days of easily serviceable carburetors.


No thanks. My EFI is easily serviceable...just replace the fuel filter every 30K miles and forget about it. Using decent quality gas will do the rest of the work.

 

[rszappa1]

My 1980 Cordoba with a 318 engine and a two barrel carter would always start up in the winter.... If your care was tuned up they worked fine. My 1968 charger with a 383 and the six pack set up would always start in the winter also... just remember to set the chock first...

 

[lexus114]

Originally Posted By: rszappa1
My 1980 Cordoba with a 318 engine and a two barrel carter would always start up in the winter.... If your care was tuned up they worked fine. My 1968 charger with a 383 and the six pack set up would always start in the winter also... just remember to set the chock first...


With all of that carburation,it should start!

 

[addyguy]

I had a 1986 Civic with a carb'd 1.5, and a manual choke.

It was a nightmare to keep running in damp weather, no matter what the temp, until it warmed up. I tuned/cleaned it within an inch of it's life, and it never got any better. One pf the main reasons I replaced it with a Toyota.......

 

[lexus114]

Originally Posted By: addyguy
I had a 1986 Civic with a carb'd 1.5, and a manual choke.

It was a nightmare to keep running in damp weather, no matter what the temp, until it warmed up. I tuned/cleaned it within an inch of it's life, and it never got any better. One pf the main reasons I replaced it with a Toyota.......


Probably needed to be re-jetted or something.

 

[Vikas]

does your snow blower starts in cold? i think it has a carburetor on it

 

[lexus114]

Originally Posted By: Vikas
does your snow blower starts in cold? i think it has a carburetor on it


It does!!

Holy.... I`m glad you told me!

 

[severach]

The choke and choke pull off required fairly exacting adjustments to start and run well. As the carburetor adjustment requirements shift over time the position of the choke should also change slightly. When not so good mechanics (like me) adjust what they don't know how things get worse. Eventually I found a way to rapidly determine the proper choke pulloff setting. I set it and it started with one pedal pump and ran fine when cold for the rest of the time I had the 1979 Omni/Horizon with the 1.7L VW engine.

Even the best choke setting is a compromise. Too little for super cold temps, just right for average cold temps, and too much for summer temps. The coolant temperature sensor takes the place of the choke and sets the exact start mixture needed for any temperature. The sensor doesn't jam up or go out of adjustment. That's why a FI engine starts perfectly and high idles at the same RPM no matter how cold or hot. The ECM can lean out the mixture rapidly based on engine temperature or oxygen sensor input instead of the fuel wasting 5 minute choke pulloff bi-metal heater.

When engines first switched over to FI I liked carbs because that was what I knew best. Once I discovered that it was possible to make a FI engine run like new for its entire life with almost no replacement parts I completely lost interest in carbs. FI also made engines last about 3x longer than ever before.

Your cars were hard to start because you didn't take the time to figure out how to adjust the chokes and keep the ignition in top shape. After a certain age your car is either fixed by yourself or by nobody. At flat rate prices noone can afford for a mechanic to do all the necessary detail work to keep old jalopies in top shape. Those without mechanical skills will have much better luck with fuel injection because fuel injected engines are entirely self adjusting based on a single sensor: the oxygen sensor. Compared to a carburetor an oxygen sensor is neither expensive nor hard to replace. Easy enough that a caveman flat rate mechanic can do it.

You people and your noisy cars. To me noise is a sign of weakness. The quieter my engines the more powerful they are.

I wouldn't run a manual choke. The automatic chokes were easy enough to fix and I didn't need to worry about other people forgetting to push them in. It was hard enough to get them to unlearn starting via pedal pumping. Starting every time with a single pedal pump wasn't good enough for them.

 

[Kestas]

I worked on carburators long before I ever learned to work on brakes. I have a simple system... disassemble the carburator completely... clean... then reassemble with new gaskets from the $10 kit... set everything to spec. Every time I did that the car ran like new.

 

[artificialist]

Originally Posted By: Kestas
I worked on carburators long before I ever learned to work on brakes. I have a simple system... disassemble the carburator completely... clean... then reassemble with new gaskets from the $10 kit... set everything to spec. Every time I did that the car ran like new.

Many carbs built during the 1980s and part of the 1970s were not like that, due to the need to pass smog tests.

 

[Jim 5]

But why do you have to richen the fuel mixture with the choke?

If I'm not mistaken it is because a sub-freezing intake manifold (in carbed days usually cast-iron) will cause the atomized fuel/air mixture to condense out onto the cold metal. This explains why there are coolant passages running through the intake manifolds on old-school cars. This cold intake dramatically lowers the amount of fuel in the air once it gets into the cylinder, making it necessary for a choke to richen up the mixture to compensate.

In a carbed car, the fuel/air mixture has to run the entire length of the intake runner before it gets to the intake valve and this creates more opportunity for the fuel in the air to drop out before it gets into the cylinder. The inaccuracy of the automatic choke just accentuates this. As the runner heats up, the amount of fuel drop-out changes and requires a different enrichment/choke setting.

This problem still exists with early TBI EFI systems but the metering accuracy from the interaction between the O2 sensor and the EFI system would have been enough to overcome it and all of the flat spots that would occur in a carbed engine as the intake manifold warmed up.

Once you get to TPI EFI, the distance that the correct fuel/air mixture has to trave before it gets into the cylinder is dramatically shorter depending on the intake but I'm guessing it would be around 6x shorter, resulting in less opportunity for fuel drop out due to cold temps. Further, the area closest to the intake valve/fuel injector will heat up faster than the entire length of the intake runner.

Finally, DI EFI systems have none of these problems and theoretically should be the best starting engines in cold temps.

 

[fdcg27]

+1.
With a carb rebuild, a car would run like new.
The three carbed Hondas we had were exactly like that.
Automatic choke?
Why?
Just give it a few shots with the accelerator pump, tap dance the throttle pedal for the first few seconds, and the beast would idle on its own even when well below zero.
I really never had a problem with the carbed cars we owned, but then I've never had FI troubles either, not even a fuel pump, knock wood.

 

[caprice_2nv]

Choke not adjusted properly is the #1 reason. My previous winter beaters with a quadrajet carb started up just as easily in -25 as my current TBI. Only difference is having to press the throttle once to set the choke. They have to be finely adjusted though and pulloff has to work.

 

[Kiwi_ME]

Many cars sold in the UK even as late as the 80's had manual chokes. It was a cultural thing - drivers didn't trust automatic chokes.

Methanol and ethanol are far worst than gasoline at cold weather starting, one reason you will not likely see an E100.

I believe the ECU in FI cars will wait until a certain cranking RPM is reached before firing injectors. Carbureted cars I've owned typically started more-or-less instantly while the FI cars have a noticeable delay, with the exception of the Saabs with Bosch CIS, which is mechanical. Same with diesels that are ECU controlled rather than mechanically injected.

 

[chrome]

Originally Posted By: Kiwi_ME
I believe the ECU in FI cars will wait until a certain cranking RPM is reached before firing injectors. Carbureted cars I've owned typically started more-or-less instantly while the FI cars have a noticeable delay, with the exception of the Saabs with Bosch CIS, which is mechanical. Same with diesels that are ECU controlled rather than mechanically injected.


Could be intentional by the manufacturer to build up some oil pressure before the engine fires and high idles.