Someone gave me a poor way of checking if the dizzy is OK. Now I need the diameter of the pulley. Does anyone have one handy to measure?
I have a good functioning basic Gunson Supastrobe. It must be at least 35 years old.
Regards, Sujit
If your timing
light does not have zeroing function (some have a knob to adjust the
light back to the TDC in order to count degrees of advance), then try
the following, which requires a little simple geometry. Measure the
diameter of the pulley. Pi * D = circumference. Let's say the diameter
is 5 inches. That makes the circumference 15.7 inches. Let's assume
maximum advance (centrifugal and vacuum combined) is 28 degrees. Divide
28 by 360, which gives 0.078. Multiply 15.7 * 0.078, which gives 1.22
inches. Measure clockwise (looking at the pulley from the front) along
outer edge of the pulley 1.22 inches from TDC and put a small paint
mark. This is your max advance reference. Start the engine and warm it
up, and then gradually raise the rpm while watching the timing marks.
If the paint mark gradually moves to the pointer as the rpm rises, then
all is probably well. If it only partially rises, then the problem is
with the vacuum advance, the centrifugal advance, or both. Disconnect
the vacuum advance and plug it. If you get the same result raising the
rpm, then the problem is with the vacuum advance. If you get less
advance with the vacuum port plugged, then the problem is likely with
the centrifugal advance. If you get little advance at all, then both
vacuum and centrifugal advance are suspect.
I have a good functioning basic Gunson Supastrobe. It must be at least 35 years old.
Regards, Sujit
If your timing
light does not have zeroing function (some have a knob to adjust the
light back to the TDC in order to count degrees of advance), then try
the following, which requires a little simple geometry. Measure the
diameter of the pulley. Pi * D = circumference. Let's say the diameter
is 5 inches. That makes the circumference 15.7 inches. Let's assume
maximum advance (centrifugal and vacuum combined) is 28 degrees. Divide
28 by 360, which gives 0.078. Multiply 15.7 * 0.078, which gives 1.22
inches. Measure clockwise (looking at the pulley from the front) along
outer edge of the pulley 1.22 inches from TDC and put a small paint
mark. This is your max advance reference. Start the engine and warm it
up, and then gradually raise the rpm while watching the timing marks.
If the paint mark gradually moves to the pointer as the rpm rises, then
all is probably well. If it only partially rises, then the problem is
with the vacuum advance, the centrifugal advance, or both. Disconnect
the vacuum advance and plug it. If you get the same result raising the
rpm, then the problem is with the vacuum advance. If you get less
advance with the vacuum port plugged, then the problem is likely with
the centrifugal advance. If you get little advance at all, then both
vacuum and centrifugal advance are suspect.
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