atc70 engine question.....

[knsmodels]

Had a friend of mine do a rebuild on my son's 70......I put it back in and got everything hooked up and it wont start....got spark got gas no run.....it seems to me that the exhaust is coming through the carb and when I put my finger over the sparkplug hole it does not blow it off.....I am thinking that the timing is out 180.....does this sound like the problem??? how much work is this to correct now that it is all together.....Thanks in advance......

[NewfieBish]

yeah it sounds like timing, im not really sure how the atc70's work but i know when the timing was off on my old 200S i used to just take a small case off the side of the motor, without even taking the motor out of the bike and move the timing chain over the sprocket.. if you really want to know if your bike is off timing, take the small bolt out of the side case, it should be on the left side, facing upwards, on the base, and if you remove it you should be able to see the flywheel moving inside of the case if you pull over the motor. on the flywheel there should be some marks, one of these (mine was a T) once this mark is in the hole the piston is top dead centre, and at this point, both valves should be closed, and there is a mark on the cam shaft sprocket to show this, so you have to make sure the mark on the cam shaft lines up at the same time the mark on the flywheels is in the hole.

[KASEY]

well he is working on a 70 not a 200.


you have to pull the little circle cover off the cam side of the head,, you will see the cam sprocket. then pull off the pull start sidecase ,, there is a "T" and a "F" mark on the flywheel... there is also a mark on the center case,,, with the "T" lined up on the case mark the circle on the cam sprocket should be straight foward between the notches in the head,, in the first pict you will see a circle on the cam sprocket,,, and the correct position for it,,,, there is just a casting line on the head to line it up with,,, in the second picture you will see the F AND T on the flywheel,,, there is a notch in the case where i drew a line that is the correct position for the "T" mark to line up on.
http://i38.tinypic.com/acev6s.jpg
http://i33.tinypic.com/w20g9h.jpg

[knsmodels]

Thanks.....I will check this next chance I get......if they dont line up how difficult is this to correct???

[KASEY]

if its not an 85 just back off the tensioner and take the bolts out of the cam. then slip the sprocket off the cam and move the chain the proper amount of teeth and put it back together,,, pretty simple