Mine came to me with a block heater. If It is away from a power source it usually needs a sniff of ether.
Ether is a powerful drug, it must be used in moderation. I spray at the air intake. By the time it passes through the filter system, the engine gets a very small dose. That is all it should have.
If that doesn't work I start a generator & use a heat gun in the air intake. Open the hood, remove the paper filter & heat the intake with a 1500 watt heat gun.
It is critically essential that two batteries be in excellent condition. Cables get overwhelming, but remember each point where two conductive object touches another, it will oxidize. Where wire (stranded) joins with a terminal it can oxidize. Copper oxide offers resistance. Each pressure connection will oxidize over time & give resistance. New, or well protected connections are needed all the way from battery to starter & back. Most machines use engine block & frame as one way current path. The faces of these connections will oxidize over time. Take the trouble to ensure each metal to metal contact is perfect. In some cases this involves adding a "ground" cable to the starter frame from the battery.
Starters need full voltage.
Batteries are able to give 60% as much power at 0 degrees F they would at 60 degrees F. The health of your batteries is very important.
In two or four battery systems the batteries must be identical.
I've heard extreme practices such as draining oil, storing it inside, removing batteries, storing inside. Even my uncle's system of building a wood fire under the engine to warm it.
