How does the chain get changed?take off and put on?

How many miles have you put on the chain.
You may just need a new chain and sprocket set.
As these do wear over a period of time.

Have you been lubricating the chain regularly ?
if this is an O ring chain, they rely on the oils in between.
If you need to change the chain, look at an X ring chain, these suffer wear less quickly.

The first thing I would do is check to be sure you didn't trip the chain break.

http://www.parktool.com/blog/repair-help/chain-installation-derailleur-bikes

Or it could be the dreaded mismatch of new chain with worn drivetrain parts...

http://sheldonbrown.com/chains.html

all chain saws have a sprocket that the chain runs on this sprocket is what make the chain rotate on the bar. the bar is the long part that sticks out in front of the motor. you must remove the side cover of the saw to access the sprocket region of the saw. be sure the saw is unplugged and then remove side cover the bar is usually held in place by a couple of bolts. on gas saws these two bolts also hold the side cover in place and must be removed to replace the bar and chain. once you have removed the side cover look for bolts holding the bar in place. if you only want to change the chain then you may be able to only loosen the bolts or screws holding the bar in place.there should be a screw to adjust the bar forwards and backwards. this screw put tension on the chain so when you put a new chain on turning the screw will proberly tension the chain /do not overtighten the chain.
also be sure you put the new chain and blade on the same as the old one that comes off trying to cut with a chain that is on backward does not work. last note if you are replacing the blade because the old one is dull take the saw to a saw shop they can sharpen the exsisting chain and save you money.

Hello yes you can change the timing chain and nothing but but it would be wise to put the two gears on at that time that comes with the chain.

The timing chain is not that fine, nor do you care about advance with the chain. A single link on the chain is more like 15 degrees, and you will have no trouble deciding which is the best fit.
TDC is always 0, and never 4 degrees advanced.
It is the ignition that is advanced, not the chain. To advance the breathing you would need to either change the cam, or get a variable chain sprocket. But again, you can not tell 4 degrees when putting a chain on. It changes that much at least when you take the slack out.

Did you put the chain back on exactly like it was? I haven't seen a timing chain in years, anyway, if you didn't get that thing right, the car won't go 10 miles without causing major damage. Did you mark it some how to the cam marks and the crank marks? If you still have it open, check it out to be sure, line up the marks to the marks on the chain, if it has them, if not, You will have to put the engine at tdc, then roll the cams to their marks, get the chain on there, spin the engine by hand a couple dozen times, pull some spark plugs out to relive the compression. Hope this helps.

your not suppose to change timming chains as long as you do your normal oil changes as such..why are you changing todays cars are having these chains so that you dont have to change a belt wich are getting absolete these days

Wind the chain through the rear sprockets, grab a hold of the rear sprocket and rotate the smaller sprocket towards the pedal, that should give you enough slack to put the chain on the front sprockets

Changing this to chain drive will require some significant expense, you may need to even change the output shaft of the transmission along with multiple case covers. You may be better off running the drive shaft to a differential. I'd suggest looking into some of the newer ATV's that run a differential and perhaps adapt one of them to your application.
The drive shaft sort of limits your ability to adjust the gearing as compared to the chain drive. You may be smarter to find a used Yamaha XS 650 engine and swap all the parts you need out of it to your turbo engine.
On another note, I used to race an OW31 Factory Works Yamaha 750 which was essentially the same basic engine that you are installing the turbo on and I'd like to caution you on cam chains. These baby's eat cam chains if you put more than 100 hp out of them. Dropping a cam chain can be VERY costly, you most likely will destroy pistons, valves, and even bend connecting rods. So if your going to put massive power out of this great little engine make sure you change the cam chain at least before you run it with the turbo. I have seen first hand what carnage happens when you lose the chain.
Best of luck and let me know if you need further assistance.
Regards,
RSelvy