2008 dr-z400sm. Always started first time, no problems. Bike has not been used for 3 weeks, battery has been on trickle charge. Bike will not start on choke, battery is fine, is it the carburetor - do I have to drain it then fire it up.

The primary requirement apart from a healthy charging system is a healthy battery and it is the problem with little used vehicles and other battery powered equipment is few people remember to periodically charge them - a battery will self discharge over time and when connected to a vehicle with an electronic system that is always "on", the discharge rate will be greater.

A battery that is left partly or completely discharged for even a few weeks will be permanently damaged or completely ruined.

As a matter of diverse interest, a vehicle "charging" system is a massive misnomer as firstly it isn't designed to recharge a battery but to keep a fully charged battery fully charged (and usually doesn't do that very well) and because of the design of the system, the "charge" rate quickly drops to a trickle charge and few people drive constantly for the large number of hours it takes to recharge a battery that is being trickle charged - a large car battery can take a week or longer...

First remove the battery, charge and test it...

As this point you can't get the bike to turn over is this correct? If the engine is turning over but won't start then yes the gas is most likely the problem. Gas after sitting for even a month can evaporate from the fuel system and it leave a fouls smelling deposit behind that clogs up everything. It stinks and it's a mess to clean out. To prevent this from happening use a product that is called "Fuel Stabilizer" in the last few tanks of gas before you put the bike away for the winter or a dormant period. If the motorcycle is in a hot climate or heated garage this foul smelling gas can happen within a few weeks.

It sounds like the battery you are using doesn't supply enough power to start the bike. Using jumper cables starts the bike because of the additional power you are supplying it. Make sure you are using the correct battery. Check to see if there is a more powerful battery available for purchase.

You have many options.
-bring it to a dealership and have them charge / test it.
-buy a charger yourself and charge it.
-buy a trickle charger and charge it yourself.
-buy a brand new battery and not worry about it for a couple years

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

sounds like the battery doesn't have enough power.
Battery may be bad, or your charging system is bad.
If the bike was sitting for a while not being ridden (longer than 3 weeks) then the battery is probably dead.
go to a local powersports shop and ask them about a "trickle charger" this is what you plug the bike into when you park the bike for a long time like the winter. You can dfind a cheap charger for about $20. It has to be a trickle charger not a regular battery charger otherwise it could overcharge and the battery could explode or even catch fire. This will keep your battery from dieing everytime you park the bike for an extended period of time.

No, the battery should charge at 14.5 to 15.0 volts. No problem. The 12.5 to 13.5 is not high enough to keep your battery charged especially if you do a lot of night time riding. You're fine.

Good Luck
Steve

Replace the plug. You should always have spare plugs on you with that bike

they make a charger called a battery tender which keeps your battery topped at all times with a trickle charge. get one and your batteries won;t die.

trickle charge 16 hours on a 1-2 amper charger /after that keep battery charged regularly ie once weekly

Your trickle charger has killed your battery. Replace the battery and all will be well.

kfx 450 is fuel injected
needs good battery to start
not enough info to diog
does the starter turn over
is it getting spark
or is fuel pump working
need more info