4 Reasons why Motorcycles Struggle to Start in Cold Weather

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The snow finally melts, the salt is finally washed off the road, and the weather is a crisp 40°F, but there’s just one problem. Your motorcycle doesn’t start. So why do motorcycles struggle in cold weather?

Engines can struggle to start for a variety of reasons, but if you notice that your motorcycle only has difficulties in colder weather then this article is for you. Some of the reasons why motorcycles are harder to start in cold weather are:

  • Cold air is denser causing lean fuel/air mixture in carburetor motorcycles.
  • The chemical reactions in a battery happen slower at lower temperatures.
  • Oils has increased viscosity (thickness) in cooler temperatures, which causes more friction.

1. Carburetor has incorrect fuel/air mixture.

Most motorcycles that struggle in colder weather or not fuel injected but use a carburetor instead. The difference between the two is the timing between when the air is mixed with the fuel inside the engine. In a fuel injected engine, the air and fuel do not meet until the fuel is directly injected into the intake manifold. The valve on the intake manifold will open allowing a mixture of fuel and air into the combustion chamber. Carburetors work differently than fuel injection. Fuel and air will mix inside of the carburetor. The carburetor sends this mixture to the intake manifold. The intake manifold divides the mixture among the intake valves, and then it finally enters the cylinder and is ignited.

Cold air is much denser than warm air. The carburetor isn’t able to automatically adjust for differences in air density. What will happen is that the carburetor will pull in the same volume of air, but because the air is denser there will be more air molecules in that volume. The increased air molecules will affect the air to fuel mixture. This could possibly cause your motorcycle engine to run lean.

2. Chemical Reactions in the Battery are Slower

Batteries really struggle in cold temperatures. AAA defines the lifespan of a battery as 3-5 years. In fact it has been determined that a battery will lose up to 35% of its strength at 32°F. Another issues is that the chemical reactions inside the battery occur much slower in a cold battery. This means that the starter motor will have less power to crank the engine.

There are a few signs to determine if your starting issue is related to the battery:

  1. Grinding or clicking noise when attempting to start
  2. Engine turns over very slowly when starting
  3. Headlights dim at idle but brighten when the throttle is twisted

If you experience these issues, especially number 3, the culprit is most likely your battery. There are a few signs to look for when trying to determine if your battery is on its way out or dying:

  • Rotten Egg Smell
  • Swollen Battery

A rotten egg smell coming from the battery most likely means that battery has been either frozen, overcharged, or has an internal short. If you smell rotten eggs coming from your battery, have it replaced as soon as possible.

The second sign is a swollen or enlarged battery. Batteries can fail when exposed to extreme cold or heat. Inspect the battery for bulging or swelling around the battery housing. In cold weather the battery can discharge and freeze. If you notice that your battery has frozen and bulged, do not attempt to charge it, rather replace it.

3. Cold Weather increases Oil Viscosity

Viscosity is a measure of a fluid’s internal resistance to flow. In cold weather viscosity (resistance) increases. This change in viscosity makes it harder for the motorcycle’s oil pump to lubricate the engine. This increased viscosity causes increased friction in the engine. The increased friction makes it harder for the starter motor to crank the engine.

4. Gas doesn’t Evaporate as easily in Cold Temps

In order for a motorcycle to run, it has to vaporize the gasoline in the cylinder where it is then ignited. Cold weather causes the gasoline to evaporate much slower than in the summer time. This has the greatest affect on the engine at startup because the engine is cold, and a large amount of fuel is required at startup. Generally winter gas uses a slightly different that is more volatile and evaporates faster than summer gas. However, most people winterize their motorcycle with a summer gas, so they do not have this benefit when trying to start on cold spring days.

How to Start your Motorcycle in the Cold

There are a few ways you can keep your motorcycle warm which will make it easier to start. One method is to remove the battery in the winter and maintain the charge of the battery on a battery tender. This will allow the battery to be taken into the house in a controlled temperature, and the battery tender will keep it charged.

Heated garages are one way to keep the bike warm. A second option is to use a heated motorcycle cover. Another option is to use an electric heater and a fan to transfer the heat to the bike’s engine. If you do this option give at least 15-30 minutes time for the heater to warm the bike up. A heated garage is a really nice option as well, but not a very practical solution if you don’t already have one.

What are your favorite tips for cold weather starts? Let us know in the comments below.