Theprevious owner went form the stock 45 to a 43 rear spocket. My chain is very loose and past the red mark on the swingarm. CanI order just a new stock chain?

 

Look on the side of the chain, there is a number stamped on the chain every two or three links. Probably 520 or 525. Count the links (for grins , lets say you have 100 links), call your local dealer, tell them you need a 100 link 520 (or 525) chain with master link for the mystery bike you didn't specify. Make sure you tell them that you need nothing less than o-ring, as a roller chain will wear out QUICKLY on the street without proper maintenance. Problem solved.

 

its a DID 520 gold. Spocket is a vortex 43. both look almost new. Maybe he kust made it too long?

 

520 Gold is a great chain, I have one on my Ducati. If you are positive it is new, you could remove a link where it meets up to the master link, and replace the master link with a new one. Again, only if you are sure it is new...looks can be deceiving, and chain snap isn't pleasant. Also, make sure you are removing it at the master link, two masters on one chain isn't good at all...back to weak links and chain snap. Or, if you have hand tools/grinder, do it the way I do. Remove the old chain and put your back wheel the whole way forward in the adjusters. Get your new chain too long, wrap it around the counter shaft sprocket and stretch it tight to the rear sprocket. See where the chain meets itself, cut there, add master link, ride. That's the cliff notes version, if you need more detail just ask.
Also, I was hasty on my first reply. If the stock chain is 100 links on a 45 sprocket, you want to take out 2 links (one inner, one outer), making the new chain a 98 on a 43 tooth sprocket.

 

so what tool do I need to do the job? going to cycle gear now.

also is this waht i need?
http://www.sprocketcenter.com/p/1037...ster-link.html

 

If you don't have the tools, ask for a "clip-type" master link...those can be installed without special tools. Just make sure the clip is installed with the open end away from the direction of travel. People may say you don't want to use that style, but they've been used since chains were invented, they work just fine...don't let them sell you something you don't need.
Also, your new chain will have a master link with it, you do not need to buy another one. If you are just shortening your chain, the DID Gold DOES have a clip-style master link available...I know this because that's what's on the Duc...don't let the dealer b.s. you.
If all you can get is the rivet style (clip type may not be stocked), I have had success installing them with vice grips and/or c-clamps. Takes a bit longer and is a royal pain, but is possible.