Hard starting after sitting around

Hmmm. My bike has been sitting unstarted since April. Today I had a hot flush and decided to ride it. Plenty of fuel with stabiliser in it, bike had been running well until I put it away (except for hot-weather cutting out), but it refused to start. The fuel pump whirred up every time as it usually does. The engine ran for a couple of seconds occasionally, then went dead, then crank, crank, crank again and nothing. Finally it ran and kept going just as the battery was dying (was fully charged with trickle charger), so I rode it hard on the highway and secondary roads for a few hours. Ran perfectly. This happened once before last year after sitting around, and eventually ran perfectly that time as well.   

These bikes don't seem to like not being started fairly often, it seems. Maybe it's a result of lots of slow running during work periods. My ancient TTR250 couldn't care less. It will ALWAYS start, even if it's been left 6 months. Ok, with some smoke I admit, but that clears...  

Btw, can anyone tell me whether the WR midrange flat spot is due to to the airbox flapper doing it's ADR thing, or whether the bike is simply lean there. Give it some more throttle and it gets through it, though.

Not just a WR-250R can do this , but more like lots of bikes, especially with the make-up of today's gasoline.
My 2013 TT-R125L, with an old-fashioned Mikuni carburetor, did not start after sitting just 6 weeks.
Taking the carb apart and cleaning the jets and passages cured it (as I knew it would).

I believe that adding fuel stabilizer doesn't mean the gasoline will be something you'd want to run the bike on after sitting for months, but is there mainly to prevent gum and varnish from plugging-up the works as it sits.
I'd drain that old stuff out.

I'm with him ^   

It's the gas.

Just drain the old gas out if bike has sat for months, and use fresh from the pump gas.

I hear you. But refer to TTR250 comment - it starts every time, without fail. Just leave the fuel tap on for 30min, and it's all go. Its fuel is as old as the WR.

Possibly new tech is a lot fussier than old tech... 

Carburetor in TTR perhaps?   

Fuel in the wr250 lines might have evaporated and it could take some time to get all the air out and the gas flowing.   

One trick I use on my bikes with carburetors is to let them run and then shut off the fuel petcock to let them burn off as much gas in the carb as possible.  If there is a carb drain then I open that up to drain the fuel from the bowl.

Doing this along with some fuel conditioner and a decent inline filter I have not had a problem letting a bike sit for 6 months or so on a tank of gas.

With my FI bikes, WeeStrom and the WRR, I typically ride them all the time so they are not sitting any more than a few days with new gas going into the tank about once a week. However as the OP states I have had instances with both these bikes starting after they have sat for a few weeks. Usually they sputter for a bit and then I have to crank away. In both cases I end up going to WOT to get the bikes to run. After they start they usually run like crap for a few minutes and then things sort themselves out. The air in the fuel lines is an interesting theory.

It I lived up north with a partial riding season I think I would probably drain the tank before putting the bike into storage since the fuel pump sits in the fuel tank.

Not that this helps you, but I left my '10 WRX in the garage from Nov 16th to mid April (5 months) without any fuel stabilizer and it started first shot with zero fuss.
Tank was full of 91 pump gas.

I have the same issue.
Over the last month there have been two occasions where the WR would not start. After cranking a lot it started both times. in both cases it had set for at least two weeks. Last week it covered 1,600 miles without an issue. Tonight after running two days ago it would not start. The bike has 26,000 miles on it. I replaced the fuel pump at 18,000. The pump runs a couple seconds until it reaches pressure then stops. I have tried cycling the pump several time before trying to start, but to no avail. A new plug was installed at 22,000 miles.