Ignition Timing Questions on E, F, and SF

[Brian_D]

In an older post (H.P. difference between 78 E & later models ) it is stated that:

The 78 had 10 degrees of initial timing and 26 degrees of centrifugal for a total of 36 degrees. The 79 F had 5 initial & 31 centrifugal for a total 36 degrees. Same deal for SF.

From Yamaha's on-line parts catalog, the E, F, and SF all use the same pickup coil assembly (2H7-81671-10-00). Additionally, Yamaha lists the timing plate for the E and F the same (2H7-81672-10-00) but the SF is different (2H7-81672-11-00); and the governor assembly is listed the same for the E and SF (2H7-81653-10-00) but it is different on the F (2H7-81653-11-00)!

Now, aside from wondering how the E and F/SF achieve different degrees of centrifugal timing with the same pickup coil assembly, I'm wondering if the part numbers listed are accurate.

[pggg]

Well these 3H3 & 2H7 units are identical and interchangeable although stamped with different numbers? but check the different sized springs, can't remember if the smaller springs are 78's or 80's, these particular units happened to have the same sized springs, but I always assume that different spring rates give differing ignition curves

[Brian_D]

so, by that pic, the only difference between the 78, 79, and 80 is the size of the springs used?

are the 80 pickup assemblies identical to the 79/79 even though they carry a different p/n (3H5-81671-10-00)?

[randy]

I'll bet that the centrifugal weights are different too.

[Brian_D]

any clue as to why Yamaha lists the same part for the E and SF but different part for the F? would think the F and SF would be the same.

[pggg]

This 2H7 has the sliding brass collar the 3H5 not, but the timing curve doesn't make any difference riding between both even with mixed parts

[79XS11F]

I would also bet that the differences are subtle but there is a difference between them. Bob-weight weight and spring differences would have an affect on at what RPM the bob-weights start to go to work. It's likely a "fine" tuning thing to ring out every possible bit of power where users like to have it.
Rob