Just 20 years ago, putting a motorcycle away for the winter months took a lot more deliberate effort, but thanks to modern advances three off months sitting in a garage is no big deal. However, not everyone is lucky enough to own a late model bike, with electronic fuel injection, sealed evaporative system, and modern computer controlled everything. And many aren't lucky enough to have a garage, or room in it for a bike.
With pretty much any fuel injected modern bike, all you need to be ready for the first warm day is to air up the tires, and charge the battery. Yes, modern gas goes bad quickly, but in a sealed tank away from moisture, it should fire right up and get you down the road for a full tank of premium.
Air it out
Depending on where and how your bike was stored, you could have any number of different varmints and critters who have moved in. In warmer dryer areas, it is mostly black widow spiders you have to look out for, but snakes or scorpions can get in there as well. Up north it is more typically mice and other rodents who find a tight safe space and make a winter home.
Uncover the bike (you did cover it so it wouldn't get scratched or taunt you all winter, didn't you?) and roll it out into an open, brightly lit area; outside, or in a more open part of the garage is fine. Just the light and air should scare away anything that has taken up residence but give them a minute or two to pack their little bags while you collect your tools.
Charge it
Batteries have come a long way, but many bikes are still using the wet cell, lead acid type that have been around for 100 years. New formulations and manufacturing has lead to improvements, but you are still lucky to get more than two years worth of use out of them. If it is time for a new battery, look into the more modern absorbent glass mat (AGM) batteries, which are much less prone to failure due to vibration or evaporation.
It will likely take several hours to bring the battery up to full charge if you have the typical, low amperage, motorcycle battery charger. So take the battery out and charge it while working on the rest of the list. This will also give you the opportunity to clean the terminals and any acid residue in the battery box.
Check it over
Now, before you actually want to go ride somewhere, is the perfect time to give your bike a complete check from front to back, and top to bottom. Lubricate the throttle, clutch, and brake cables (where applicable) and controls with a light spray lube, and if you have older mechanical, cable driven instruments, oil them up too. Pop open the gas cap and look inside with a flashlight to check for signs of that evil villain, rust. This is a perfect time to lubricate the gas cap hinge pivots, and latch mechanism too.
If you have an older bike, with the simple, manual petcock, spray a bit of lube on it, so it seeps into the pivot mechanism and rubber seals. Check over the rubber lines from the tank/petcock to the carburetor or fuel pump looking for cracks or other signs of degradation. While you are in the neighborhood, lubricate all the rest of the throttle linkage too. Pop open the air box and make sure no one had made a nest in there, then check if the filter needs cleaning or replacing.
Move to the front wheel, and check for tire wear, proper inflation, and brake pad life. Turn the handlebars from side to side and check for any notchy feeling in the steering stem bearings. Jack and support the bike so the front wheel is off the ground. If the steering bearings are in good shape, properly lubricated and adjusted, the wheel should flop over easily from side to side with just a little push. Grab the wheel and check for any play in the steering head by trying to push it front to back, and side to side. Finally, look at forks where the tubes meet the sliders and look for signs of a blown seal; you can usually see an oily residue with dust stuck to it.
Now move to the back wheel, and check out the rear tire and brake pads for wear. Check the condition and tightness of the drive belt (where equipped), looking for any tears or damage, and make sure it still has the proper tension. On chain driven bikes, look for any seized links that don't pivot freely, clean, adjust and lubricate the chain before going riding. Shaft driven bikes are nearly maintenance free, but you do need to check for the proper level of gear oil periodically. On all bikes, with the rear wheel off the ground, check for side to side movement that would indicate worn out swing arm bushings. Finally, on drum brake bikes, check how far the brake cam arm will pivot to see how worn the brake shoes are; replace the shoes or adjust the free play to proper spec.
Maintain
Did you catch up on all the maintenance your bike needed last year before putting it away? Then you pretty much just need to put the battery back in and roll!
The reality is that the proper time for oil changes and valve adjustments is before you put the bike away for the winter, especially oil changes. Oil builds up water and contamination over time, especially on bikes that aren't ridden hard or often. Changing it before you put the bike into storage keeps things from corroding inside of the motor while it sits for a few months. Brake fluid should be flushed and refilled every other year as well for the same reasons.
Check your manual for proper valve adjustment intervals (you may be surprised at how frequent they are) and procedures. On many older bikes valve adjustments can be done by a home mechanic with nothing more than a set of feeler gauges, sockets, screwdrivers, and wrenches. If the adjustment involves shims it is a bit more involved and you will either need a shim kit, or to measure everything precisely and buy just the needed sizes, which you may be able to do from your local shop.
If the bike is liquid-cooled, the coolant is typically good for five or even ten years, but be sure it is always topped off. But don't forget, if you do a track day and replace the antifreeze with pure water, you need to drain and refill with the proper coolant to lubricate and protect the internals when you are done.
Carburetor cleaning
Did you turn the petcock to "off" and run the bike completely out of gas before putting it away? That and a shot of fuel stabilizer is often enough for three or four months of storage.
The most dreaded part of waking an older bike from winter hibernation has always been the carburetors. In the old days of carbs with float bowls vented to the air and easily evaporated fuel, the float bowl would be covered in varnish, or worse, full of corrosion come springtime. Cleaning them required removing them, soaking in a solvent, and making sure all the tiny fuel passages were clear.
Fuel doesn't evaporate as readily these days, and the bowl vents typically go to a charcoal filter which limits how much moisture can get inside, so things are easier on more modern bikes. Take off the float bowls and look inside and you will either find some old fuel or the varnish-like residue of it. On occasion, if the bike was stored outside, you may find signs of water contamination.
Dispose of any fuel you find properly, clean the bowls with carb cleaner and set them aside. If the bowls look good, you can likely get away with a few shots of aerosol carb cleaner in the jets, and the float needle valve. On an older bike without a fuel pump, turn the petcock and check that a dribble of fuel comes out of each carb.
As we always say, "Assembly is the reverse of disassembly". If possible, put a small amount of fresh gas in the float bowl before replacing it on the carb.
Fire it up
Now all that is left is replacing the battery and pushing the button, or kicking the starter lever. If all goes well, you should be off to the races after just a few minutes of warm-up and throat clearing.
