How do I replace sidestand cutout switch

sidestand cutout switch sticking...

Replace the steel plates you sanded down. These wear down as they are being used, so you have basically taken a couple of years use off them. You might want to make sure the engine is breathing properly- petrol and air filters. If the engine is stalling when you put it in gear then the engine is either not running right or there is a safety cutout switch somewhere that is telling you the sidestand is down. Also check you have the idle set properly.

Okay.....I think you have a sidestand switch problem.
Do you notice that if you leave it in gear after it stalls....that even with the clutch in it won't crank the starter?
The sidestand switch is a plunger that presses in when the sidestand is down. The interlocks on the RS require that to start the bike...with the sidestand down, it must be in neutral. If you place it in gear which the sidestand down, it kills the ignition to prevent riding off and snagging the stand on the road etc..
So if you had the sidestand up before placing it in gear.....since the bike sat for a year...I suspect the plunger for your sidestand switch is stuck partially in (its been pushed in for a year!)
Find the switch down by the sidestand pivot....have someone hold the bike or support it so you can raise the stand, and spray some WD40 on the plunger and work it in and out letting it snap out several times then try it again.

You don't mention the year and model...but here are some general ideas.

Most Yamahas have various safety interlocks designed into the wiring system....typically a neutral switch, a sidestand switch and a clutch switch, a tipover switch and a kill switch on the right handlebar.
The design basically is to prevent riding off with the sidestand down....so if the bike is in neutral, the neutral switch grounds to light your neutral lamp and allows for ignition and starter operation.
Is you place the unit in gear...if the sidestand switch senses the stand is still down, it kills the ignition and starter.
If the bike is in gear, starter will not operate, unless the clutch is pulled in and the clutch switch detects this happening.
Tip the bike over and the tipover switch kills the ignition and fuel pump if it has one.

So...is the igniter (black box/brain etc) getting supply voltage...if not check the ignition fuse, and the handlebar kill switch .
Is the neutral light working....if not...try starting with clutch in and sidestand up.

worth checking the sidestand cutout switch as they're a known issue with many bikes

try driving it around stop at a few places...do not put kickstand down...then see if it starts, does it start every time? if it does, then you have a bad kickstand cutout switch. hope this is the problem. let me know
Thanks.

First guesses are a weak battery or starter relay going bad. Next time it does it, keep pushing the start switch rapidly and see if it catches. If so, the relay is going bad.

What make bike???? there is an automatic shutoff switch on kickstand on Honda Bikes when put kickstand down automatically shut engine off If bike sitting in damp envirmoment over winter may cause it to shoot off soon as you put it in gear SO CHECK KICKSTAND SWITCH...HOPE HELPS

Sidestand must be retracted and sidestand switch functioning or the engine dies as a safety feature to keep you from riding off with the sidestand down. If the sidestand is up and it still dies, disconnect the sidestand switch and put a jumper in there. If the problem goes away, your switch is faulty.

new battery in itturning over nicely after chasing down a few bad grounds but have very weak spark.I had cam2 in it even and couldnt get it to fire.I suspect coils or possiblly grounds still .Question iswhere can I get these electrical parts for the bike?(dont all answer at once now...)I think I need pickups for the bike as well but am going from memory on that one.ThanksHave you tried changing the ground from the coils to go straight to the frame and NOT through the sidestand cutout? I don't trust that little fella. I've rewired mine so it kills the satrter motor instead - can't start the bike with the sidestand down - and as I never get off the bike leave the engine running with the sidestand it's not a problem. It does mean though that if the switch gives problems (i.e. in the wet) it does not kill the engine.,,,