Here is how to read “Base Advance” and “Max Advance” just by reading the flywheel.
The “T” mark is Top Dead Center
The “F” mark is Fixed/Base Advance at idle.
The “| |” mark is the range of Maximum Advance.
When the timing is checked with a timing lamp, The “F” mark should appear to be lined up with the TDC mark on the engine case when the engine is idling.
The TDC mark on the engine case is lined up between the two marks “| |” at maximum advance. (Usually medium to high revs)
Above is the flywheel of a Pitbike Lifan 140, the TDC mark is the little notch on the case.
By printing a Timing Tape with the help of this great website, you will be able to directly measure base advance and max advance on the flywheel.
1) Print one Timing Tape.pdf according to the circumference of the flywheel.
(ie: pdf for a 110mm diameter)
2) Align the “0” of the timing band with the “T” mark. Scotchtape the ruler.
3) Note the degrees value facing the “F” mark. This is “Base advance.”
4) Note the degrees value facing the “| |” mark. This is “Max advance.”
Base advance is 15° BTDC at idle (“F” mark).
Max advance is between 33° to 37° BTDC at high revs (“||” mark).
You can also use the ruler to measure the length of the tab.
<Base Advance> + <Length of Bar> = <Max Advance>
This tip is particularly useful when the flywheel doesn’t have the “| |” marks engraved: Just add the length of the bar to the degrees read at “F” mark to get the Max Advance.
Below the length of the bar is 20 degrees. 15°(“F” mark) + 20° = 35°