My 1998 yamaha v-star sat for about 3 months and now won't stay started unless the choke is out

SOURCE: Yamaha v star 650 runs with choke on only

That is the problem,You need to clean the carb jets and get the gum out of the bowl.

SOURCE: Yamaha TTR 125 L won't idle

The problem is that your idle is adjusted to low just like mine, you need to adjust your idle

SOURCE: 03 yamaha yz250f runs with choke on but wont idle with choke off

No Yahama No Piano

SOURCE: motorcycle runs with choke only?

You can try a good fuel additive such as "Seafoam" . Put it in the tank. The more the better to "clean out the carbs". Start her up and let it do it's thing. Let it just idle for a while and try to open the choke. If this does not do the trick. Then you will need to remove the carbs and take them apart and clean them-sorry. When you think you are going to let her set up for 2-3 months, run some Sty-byl fuel additive in your gas. 

SOURCE: 2001 v star 650 classic won't idle after being stored

You have a gummed up mainjet. Always store a gas engine with Staybul gas additive to avoid this problem in the future. Now, on to the current problem. Since the bike will at least idle your in luck. Just go down to an auto parts store and get a can of Sea Foam. I usually find it at NAPA it's a white can that looks like it came from a gas station in the 1940's Because it did. Mechanics have been useing it for years. Anyway, dump about half the can in the tank with a couple gallons of gas and fire it up. Let it idle a long time. Then start trying to ride it. You may have to let it set over night if it's really gummed up but it will clean it out. Easy fix, and you can leave it in with no problems. Happy motoring.

Testimonial: "Thanks, got it going and seems to be running fine now."