does anyone know how to set the timing on a 1999 yamaha yfm 250 it jumpet time an i need to know what marks to line it up with

 

There should be a plastic plug on the top side of the left engine case, and a bigger one on the side, the top one , when removed, is where you will see the timing marks, the side one is where you put your socket wrench on to turn the motor. Remove the sparkplug, this will make it easier to turn over, and relieve pressure that will make it want to "turn over" when you get to TDC. slowly turn the motor CCW with the socket, you should see an "F" followed by a "T", line up the notch in the cover hole with the line on the flywheel by the "T". Then remove the cam chain cover on the side of the head, exposing the sprocket and chain for the cam, there should be a dot on the teeth of the cam sprocket, and at about the 10 or 11 o'clock position on the casting of the head, there should be an arrow or a line, the dot must line up with that when the "T" mark is lined up on the lower part of the motor. That is how it is on my 1995 350, should be the same for your 99 250.

 

if anybody can give me a hint in how to replace my rear sprocket on my 2005 450yfz thanks.

 

If it is the factory chain, you will need a chain breaker to take it off, then you will need to remove the wheel and possibly the hub on that side, the sprocket may not fit over the hub. There should be 4 metric allen head bolts holding the sprocket on,hit them with a little penetrating oil to help loosen them. Then remove the sprocket, if it wont go over the hub, you will need to remove that as well. Install new sprocket, loosen chain adjustment to allow remounting of chain (you will need an 0-ring master link to match your factory 0-ring chain) , put hub and wheel back on, re tension chain, and you should be good.

 

thanks i tought it was going to be a lot easier, but it seems like i might of underestimated the work involve. Thanks again.

 

It's not really that complex, the chain breaker just pushes the pins out of a link so you can take it apart and remove it. 4 bolts to remove sprocket, 1 nut on hub if sprocket won't fit over hub (you can just save steps and remove the hub and wheel/tire as one piece). The hardest part is just compressing the o rings on the new master link so you can put the retaining clip on, then you just bolt the new sprocket on and put the hub/wheel assembly back on. I'm sorry if I made that sound involved, with the right tools, you could have this done in 1/2 to 1 hour, depending on your skill level. If you get a buddy to help out, you should be able to do it easy.