Please help

Hi all, i have a 08 WR250X. Only mod is an FMF Q4 with servo eliminator, 1200 miles. The issue im having is if i let bike sit for a month or so, its really difficult to start. Battery seems fine, use a tender, fuel pump primes. When pressing start button it just keeps trying to start. Finially after giving it a bit throtte it will start. Sometimes a backfire will occur. It will idle fine. All seemed ok....this was in April. Now since then i would just go out to garage and fire it up every few days and it would start right up.
Today i wanted to take it for a spin. It fired right up, i let it idle for 5 min. Started down the road and it died out. Tried to start up and had trouble again. Once i got it started i had to keep throttle in it or it would die out. Now it doesnt want to idle or keep running unless throttle is on. I know about kick stand sensor etc, put fresh gas in April when 1st having issues.
Any ideas or suggestions would help guys.

Check air filter compartment. Make sure it's clean and clear of things like mice and nests and such.

April gas is old gas. 

Drain it, use it in lawn mower or car or something. 
Get fresh, new gas. 

Bikes that sit for long periods of time get gremlins. 

Wires get chewed, hoses dry rot, and things clog.

Thanks for responding, the air box is super clean, freshly oiled K&n. Bike its self super clean. I keep it in a super dry garage.Just changed oil in April. Im kinds clueless at this point

Have you checked your plug and coil?

No, Thats my next thing i guess i can look at

One guy here once had a cracked spark plug.

There's plug between the gas tank and radiator that's given a person or two fits over time. 

You absolutely sure the battery is good?

Does the bike have the original fuel pump?

Orig fuel pump. Its priming when i turn on key.
Yea i think batt is fine, doesnt have that weak feel when starting bike

These bikes are REAL finicky when it comes to electricity and batteries. 

Considering you have a bike that's between 5 and 6 years old with only 1200 miles on it you're not riding it much. 

Not saying the battery IS your problem, but "guessing" it "feels" right isn't ruling it out completely either. 

Thanks again guys, im gona start with Battery and also just go ahead a change plug. Will advise

Ok today i pulled the plug and ready to install a new NGK CR9EK. Got to run to store and grab some anti-sieze.  Yesterday ordered new YUASA battery.
Will advise if these fix my issues.