Why Carbureted Cars Are Hard to Start When Cold

[Propflux01]

Originally Posted By: chrome

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


That may very well be, because as soon as it fires, it is immediately brought to a high rpm to fire off the Cats.

 

[65cuda]

Actually I've had a few that started better than my fuel injected cars have. The 69 cutlass and 78 Chevy van 4 barrel quad were two of the best. Start right up in the coldest of weather and be good to go. Of course on the other hand the 65 barracuda with the commando v8 was every bit the exact opposite. I tried and the mechanics tried but it NEVER started worth a darn in cold weather.

 

[johnd]

Problem is with carbs that there weren't that many people that were any good adjusting them. I had 5-6 carbed cars in the 60's and later and they all performed flawlessly as did the ones owned by my dad. They do require some maintenance and periodic adjustment but during those days you had to do more maintenance anyway. Spark plugs were 3-5K miles in those days. In fact, I'm so used to maintenance activities that sometimes I feel like I'm ignoring the needs of my newer cars. I have one right now with no grease fittings on it anywhere. Feels weird.

 

[lexus114]

Originally Posted By: 65cuda
Actually I've had a few that started better than my fuel injected cars have. The 69 cutlass and 78 Chevy van 4 barrel quad were two of the best. Start right up in the coldest of weather and be good to go. Of course on the other hand the 65 barracuda with the commando v8 was every bit the exact opposite. I tried and the mechanics tried but it NEVER started worth a darn in cold weather.


I hear that! My older 3.8 liter GM cars would barley crank and fire right up! My RX cranks a few times before it fires? Warm,or cold.

 

[Vikas]

Honda was one of the last hold out until they went to FI cars. I had a Prelude few decades ago which was dual Mikuni carb'd. As long as you pumped the gas pedal "correct number of times" for the outside temperature; it would start right up. Sometimes, I had to do little bit of pedal dance.

- Vikas

 

[lexus114]

My brother in-law had a prelude. He still talks about that car.His was fuel injected though i believe.

 

[440Magnum]

I'm going to give a two part semi-self-contradictory answer.

First- when everything is adjusted correctly carbureted cars light off darn near as well as EFI. It DOES require operator intervention- one or two pumps of the pedal to let the choke snap shut and squirt a priming shot of fuel into the plenum... but they'll light right off and run. However, they'll be ill-tempered even when things are set right- the idle will be ratty and possibly smoky for a few minutes, and they're prone to stalling.

Second- the reason they're ill mannered is because EFI (multi-port) fires the fuel right at the back side of the intake valve just as its sucking the fuel/ air mix into the cylinder, so even if the fuel doesn't want to atomize all that well due to cold, it still gets into the cylinders in the right proportions. Carbureted cars introduce the fuel in one spot, and it can condense out and get poorly distributed along the way with some cylinders drowning in raw fuel and others running lean. Throttle-body injection is prone to that also, but since the fuel is forcibly sprayed (even at idle) in TBI, its not as bad. When the choke is set and a carbureted car is idling, the air/fuel flow is low and the fuel tends to just dribble in out of the main jets due to the choke being set- the idle circuit still atomizes well, but the extra enrichment (due to the choke) doesn't.

 

[artificialist]

Originally Posted By: 65cuda
Actually I've had a few that started better than my fuel injected cars have. The 69 cutlass and 78 Chevy van 4 barrel quad were two of the best. Start right up in the coldest of weather and be good to go. Of course on the other hand the 65 barracuda with the commando v8 was every bit the exact opposite. I tried and the mechanics tried but it NEVER started worth a darn in cold weather.

Is the Commando V8 the one with the cross-ram manifold, 2 carbs, and very long runners?

Those were trouble because gasoline had more time to condense inside the manifold.

 

[440Magnum]

Originally Posted By: GMBoy
Let's not forget, too, that today's gasoline is not ideal for carbs and that just makes matters worse.


You speak the TRUTH. Winter fuel in particular sucks rope. They raise the vapor pressure in an attempt to make it atomize and burn better in the engine, but what really happens is that my '66 will vapor-lock on mildly warm winter days, even though it can tolerate 110+ degree days with the AC running and sitting in traffic during the summer with lower vapor-pressure fuel.

Winter blend gas, IMO, is a scam. Its a way for politicians who don't have a clue about engineering to think they're "doing something good" by mandating it, and its a way for the refiners to get rid of their really [censored] highly volatile stocks that wouldn't make the cut for summer blend gas.

 

[440Magnum]

Originally Posted By: artificialist
Originally Posted By: 65cuda
Actually I've had a few that started better than my fuel injected cars have. The 69 cutlass and 78 Chevy van 4 barrel quad were two of the best. Start right up in the coldest of weather and be good to go. Of course on the other hand the 65 barracuda with the commando v8 was every bit the exact opposite. I tried and the mechanics tried but it NEVER started worth a darn in cold weather.

Is the Commando V8 the one with the cross-ram manifold, 2 carbs, and very long runners?

Those were trouble because gasoline had more time to condense inside the manifold.


Youre' thinking big-block- the one you're remembering was made in 383, 413, and 426 CID displacements. The ones made for street use actually were not too bad in the cold because they had special exhaust manifolds that bolted up to the bottom of the intake right underneath the carb to heat the floor of the intake very quickly and help fuel vaporization. Kinda detracted from ultimate performance, but sheesh- those things had power in reserve and didn't need every gnat's wing of advantage.

The Commando that a 65 Barracuda would have had is the smallblock 273 Commando- single 4-barrel on a conventional manifold, and one STOUT little motor. The Mopar smallblocks always were especially ill-tempered in the cold for some reason. They threw enhanced manifold heat (exhaust crossover), electric-assist well chokes, and all sorts of stuff at them, but never really made them where they'd light right up and run like the big-blocks did. I've owned and love both, but the only way to get a smallblock Mopar to run right in the cold is to go with an electric choke on something like an aftermarket Edelbrock (Carter clone) or Holley carb. When I was driving my smallblock, I discovered that you could bolt a modern Edelbrock electric choke kit right on a stock Carter AVS or AFB carb and it changed the whole personality of the engine.

 

[severach]

Originally Posted By: Kiwi_ME
I believe the ECU in FI cars will wait until a certain cranking RPM is reached before firing injectors.

It's because the engine must crank about 1 time around before the ECM knows the crank position. Not firing at all is better than firing at the wrong time.

 

[artificialist]

Originally Posted By: severach
Originally Posted By: Kiwi_ME
I believe the ECU in FI cars will wait until a certain cranking RPM is reached before firing injectors.

It's because the engine must crank about 1 time around before the ECM knows the crank position. Not firing at all is better than firing at the wrong time.

Depends on whether or not sequential injection is used.

Some batch injection engines only have a cam sensor on the distributor, and it injects fuel on all cylinders each time the spark fires on one cylinder. Those engines would not have to wait.

Some banked injection engines use only a crank sensor, and 2 injectors are fired simultaneously the same way that the waste-spark coils are fired.

A cam sensor failure in a sequential injection engine with individual ignition coils or waste spark coils can (in some designs) revert to firing 2 injectors simultaneously.

 

[mechanicx]

On GM SEFI all the injectors fire once simultaneously for a priming shot and then 1 or 2 revolutions is counted to allow the fuel to get drawn in. After that the injectors start firing in sequence.

 

[cousincletus]

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.


I was a little bit lazy about rebuilding my carburetors. I would just replace the accelerator pump and top gasket w/carb still on the car. Check the bowl for trash. If there was any, slop it up w/paper towels. Slap it together and it would run as well as a rebuilt carb. The pump is what goes bad on those things anyway, so I felt there was no need in making extra work for myself.

 

[65cuda]

Yeah you are right that it was the 273 engine. It ran great once you got it started and it started good in warm weather. I was told it was because of the cam lift that it didn't start good, but evidently that wasn't so. Thought about changing it to a manual choke but got rid of it before the next winter came along. Driving the 4 speed in town got a little old after a while. Still though I kind of wish I had it now along with the Cutlass.

 

[mechtech2]

With a carburetor, the fuel is far from the intake ports and combustion chambers.
On some vehicles, the manifolds are pretty horrible about this.
A straight six with a one barrel carb, for example.
When you pump the pedal , the squirted gas just sits there. In the cold, it does not vaporize readily. The engine is starving for fuel.

When the engine is warmed up, the fuel is not liquid in the manifold, but vaporizes for better distribution and flow. So far less problems occur then.

On carbureted cars in real cold weather, I pump the pedal 2-3 times and let is sit before cranking it over. Give it a chance to vaporize a bit. This is a good way to minimize the inherent problems, and works pretty well.