1997 yamah yz 125 lots of white smoke comeing out of pipe

Sounds like either a blown motor (rings need replaced) or a bad head gasket or cracked head.
If the rings are bad your car would have felt like it was losing power because the engine will no longer have the same high compression that it's required to turn the wheels. You may have heard your engine knocking or seen a light blue colored smoke coming from your exhaust as a result of your engine burning up oil in the combustion chamber from the rings leaking.
If your head gasket is leaking or your head is cracked you'd likely find milky looking oil when you drain your oil from water/antifreeze being mixed in and noticed a white smoke coming from your exhaust that is actually water vapor coming through the exhaust.
If your car was running rough when you last shut it off try pulling all of your spark plugs and either cleaning them or replacing them all. A bad head gasket or bad rings can both foul spark plugs. A car will run rough with 1 or 2 fouled plugs, but once enough foul it will no longer run at all just sit and crank over. If changing the plugs get's it started for ya, check your tailpipe first for water, if nothing, change your oil. If no signs of water/antifreeze or milky colored oil then it's probably rings.

if your still fouling plugs then you still need to go with smaller # on main jet...are you spooging allot out of pipe and muffler? then your to rich still,smaller jet size!!!! 32:1 is a good mix ratio

A bad crank seal on the right side, if bad, will **** transmission oil into the combustion chamber. This will smoke badly.

Run a B9ES if you don't have a problem with fouling. If you do have a problem fouling, run a B8ES. Both of these plugs are available at auto parts stores for a few bucks each.

The stock plug was a BR9** - the R indicates a resistor plug which is not needed.

Scott

white smoke is an indication of a leaking headgasket. if this is the case the coolant could have fouled out the plugs

first off make sure the oil gas mixture is correct and mixed very well.... have the carb cleaned out very well or even rebuilt, jetted and adjusted...

Hey Ryan! Long time since hearing from you.

When you say "main clutch casing" do you mean the right side cover for the gearbox or do you mean the primary driven gear (AKA "clutch basket") that the clutch boss (AKA "clutch hub") and all the clutch plates fit into?

If you mean the right outer casing > they are slightly different, '97 pn 4JY-15431-10-00 and 2001 pn 4JY-15431-12-00. The entire clutch is the same from 1997 through 2001.