How do you know when the magneto is at tdc? Also, does the spakr plug fire every other stroke, (2 of 4)? If not, how does it know when to fire on only 1 of the 4 strokes?
Thank you,
-Dennis
Take magneto cover off find tdc on the magneto and look at the cams it should be after the inlet valve shuts and goes on the firing stroke just put a rod in the cylinder and see if the piston reaches the top off the bore when the magneto is at tdc then its fine buddy any probz im here to answer
SOURCE: how do i set the timing on a yz450
Set the piston to TDC (top dead center) this is the higest point the
piston will rise before moving on to the down stroke, either by lining
up the marks on the crank rotor or a long screw driver (large handle so
it wont fall in) down the plug hole and watch for the highest point lock
or hold at this point. If cam sprocket has marks line them with the cylinder head surface (sometimes the sprocket bolts) parallel.
The cams should be fitted next on the
'compression' stroke meaing the all valves should be closed when the
cams are seated (no valves being pressed by cams) generally at this
point the cam lobs face away from the valves , next stroke down (ignition
of fuel) valves should be closed with the exhaust cam moving round
ready to rock on to the exhaust valve as the piston rises to the top
again (4th stroke exhaust) as the exhaust valve lobe rocks off the
intake cam lobe should be starting to rock on opening the intake valve
on the down stroke of the pistion.
Trun the engine over by hand to make sure no valves are knocking the piston.
Should be as follows
1.
all valve clearance free/rocking at ' TDC 1st 'down' stroke (ignition
of fuel) valves closed exhaust moving round but not pressing valve ,
2.
2nd stroke 'up' exhaust valve rocking open and closing as piston tops
with the intake ready to rock on as the exhaust closes and piston tops
(exhaust),
3.3rd stroke 'down' (intake of fuel) as the piston moves down the intake valve should be opening.
4.
4th stroke 'up' compression of fuel all valves rocking closed as the
piston rises for the compression stroke back to TDC all valves
closed/rocking free.
Intake, compression , ignition and exhaust. (**** squeeze bang blow)
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