just got a new bike last week, havent been on it for more than 15 miles give or take and am changing something with the back wheel, i put the bolts back on and tighten then i spin it(the bike is on the saddle and handlebars on the floor) and the chain tightens, then slacks,then tightens each rotation by a GOOD amount, what is causing this and how the hell doifix it? its a brand new chain, thank you.

My guess is that most likely a not very round chainring.

My first thought would be an out of round cog or chainring. If you bought a lower-end complete it isn't that unlikely.

Or you're unknowingly using a Biopace

You may just need to center the chainring.

You can try adjusting the position of the chainring on the cranks. It takes a lot of patience, but it's a good skill to have if you like to mess around with gear ratios.

https://www.sheldonbrown.com/fixed.html. See the section on Centering Chainwheels.

its not going to cause me to crash or anything though is it? its only about an inch of give per rotation then it tightens back up.

As long as the chain doesn't get so loose that it can come off the chainring or cog, then it's not a problem. Position the cranks in the position that makes the chain the slackest and try to remove the chain from the chainring. If you can't, then you should be ok.

Yes this could cause a crash on a fixed gear. If your chain gets so loose that it can fall off, it can wrap itself around your cog and bad things happen. Your wheel can lockup, and you will almost certainly mess up the paint on your new bike.

You should get this fixed if there is a large difference in chain tension. If you are setting the chain so tight that it binds, you will wear out everything much faster. First try repositioning the chainring as mentioned Sheldon's link. If that doesn't work you probably need a new chainring.

If you bought this bike from a shop, take it back and have them fix it. It is completely unacceptable for a brand new bike to be sold like this from a shop. If you bought it online or something, you will have to fix it yourself.

its a vilano. doesnt surprise me.

Well my concern is that is wasent doing this previously, took it out for a couple miles today and took it home and BAM it started doing it after i took the rear bolts off to adjust. it wasent doing it previously... and the jump from tight to loose isent enough to throw the chain. Is there anyway i had the chain too tight for the past few days ive been riding and somehow it messed everything up? there was no slack in it what so ever, i know you need some but i couldent get the right balance and it looked terrible with the chain slacking so much(a good few inches) so i said **** it and rode about 8 miles with a superrrr tight chain...

It sounds like your chainring bolts worked themselves loose, and the chainring shifted. At the very least, you need to check that the bolts are properly tightened.

I had the same problem with the All City Big Block I just bought. I just changed the rear cog out with an EAI cog that I had laying around and it helped tremendously!! I still do not have perfect tension all the way around but I never have had it with any FG/SS I have had.