by Bill Unger
Advance = the amount of angular
measurement that the spark happens before the piston reaches top dead center (TDC)
on the power stroke.
is less amount of advance
combustion engines need to start the combustion fire before the piston reaches
TDC because it takes an amount of time to get the gases burning. The spark
happens before TDC, this is called BTDC. If you donít start the gases burning
BTDC a lot of the energy will be lost. Obviously making the burn happen at the
right time is important in the production of power.
automotive engines have a mechanism to change the ignition timing as the
revolutions per minute (RPM) goes up. The faster an engine turns the ideal time
of ignition varies (the faster it turns the more advance is needed). Yamaha RDs
do not have an ignition advance mechanism. Some automotive engines have
mechanical advancers and some have electronic advancers. Your bike has neither.
The specification from Yamaha is that the ignition happens at 2.00 MM BTDC. They
could have said 19 degrees of crank angle but that is harder to measure. You
would need some kind of degree wheel attached to the crank to measure degrees.
With a dial gauge you can measure 2.00 MM BTDC, which is a very good substitute
for angular measurement.
how do I time the bike??????
you have a dial gauge you use it to make sure the ignition marks on the rotor
and stator window line up at the time you want ignition to occur. If you do not
have a dial gauge, I guess you have to trust Yamaha that they manufactured the
bike with some quality controls in place and the marks are at least close to
correct. Before you attempt timing you need to make sure the ignition points are
set correctly. Why? Because the
coils need a minimum amount of time to saturate (gain full charge). The manual
suggests a point gap of 0.3mm. Make sure the points are all the way open before
measuring and adjusting and make sure they are clean. Wipe them when they are
closed with a white business card (you know the kind that a businessman has with
his name and address on it). When the points are closed, open the points with
your finger and insert the card (.25mm white card stock will work) close the
points and slowly remove the card without tearing. Do this until the points
leave no mark on the white card stock. Timing the bike you want the points to
open at exactly the same time as the timing marks come into alignment. If you
have timing light this is easy to do. But in case you donít have a timing
light you can use an ohmmeter to do the same thing. Hook up the meter and watch
it and the timing marks at the same time. As the marks come into alignment the
needle on the meter should swing from 0 ohms to infinity ohms. Oh you donít
have an ohmmeter?????????? Try this little trick; the ignition switch needs to
be turned on for this trick to work. What you do is hook up a small light bulb
(12V) to the ignition points as one connection and positive terminal of the
battery as the other. The points are closed sending electricity through the
condensers to earth, hence the bulb doesnít light up. When the points open the
coil fires and your bulb lights up at the same time. You want your bulb to light
up as the timing marks align. Simple?
next frontier. Since you do not have an advance mechanism on your RD you have to
chose a number and live with it. 2.00 MM will be OK both top and bottom. You
have to decide what is best for you. Be careful about advance. Some gasoline
works better than other gasoline. Some like advanced ignition timing(93 octane
and more), other gasoline does not like advanced ignition timing(87 octane).
Hence if somebody says retard your timing they mean make it fire closer to TDC or with less advance.