Lucas K2FC Magneto AAU Advance Curve

[Britstuff]

Hi All:

Recently installed a rebuild K2Fc Magneto in my 1962 650 SS. Thank you Doug at Doug’s Cycle Barn for the rebuild. Was sad to read about the passing of @texasSlick, His instructions regarding how to setup a Lucas K2F Magneto were invaluable.

I decided to use a strobe light to check timing while the bike was running. Accordingly, I marked the stator ring at TDC, 8 degrees BTDC and 32 degrees BTDC. For the most part everything appears to be set correctly: the bike idles at around 8 degrees BTDC and advances to 32 BTDC when given the beans.

However, what I did not expect is that full advance (24 degrees at the crank) was achieved at only 2,250 rpm. Is this normal??? Maybe the springs on my AAU are a bit weak and need changing???

 

[robs ss]

I'm no expert on this, but as far as I know there is no "curve" for the springs, they're just meant to be fully stretched (advanced) before 3000rpm
If it sounds good at 2500rpm then I wouldn't worry. Pinking at this rpm would be a sign of too much advance below 3000rpm.
Cheers

 

[robs ss]

Quote from the magneto section (136 on p58) Norton Service & Overhaul Manual by F. Neill (covers all the Nortons from the early-mid sixties)

"At 1600 engine r.p.m. the unit begins to advance the timing. At 2000 r.p.m. there can be from 10 to 20 degrees advance, and at 2500 r.p.m. and above, the unit moves to the fully advanced position giving approximately 24 degrees."

 

[Triton Thrasher]

Feel free to try other springs. Some are likely to be stronger than others.

 

[Britstuff]

Quote from the magneto section (136 on p58) Norton Service & Overhaul Manual by F. Neill (covers all the Nortons from the early-mid sixties)

"At 1600 engine r.p.m. the unit begins to advance the timing. At 2000 r.p.m. there can be from 10 to 20 degrees advance, and at 2500 r.p.m. and above, the unit moves to the fully advanced position giving approximately 24 degrees."

Thank you for your helpful replies.

Sounds like the rapidity of advance on my bike is nowhere near as odd as I thought. Maybe in fact close to, or normal.

in regards to your earlier question about how it runs…. Running on the center stand, no evidence of pinking observed. Seems to rev smoothly to 3000 + rpm. As soon as the weather permits I will take her out for a test run. Sounds like maybe a typical case of me inventing my own problems!

Cheers!

 

[Britstuff]

Feel free to try other springs. Some are likely to be stronger than others.

Thank you.

It sounds like new spring strength is a bit of a lottery. Have you or ever come across a consistent source?

 

[robs ss]

in regards to your earlier question about how it runs…. Running on the center stand. no evidence of pinking observed. Seems to rev smoothly to 3000 + rpm. As soon as the weather permits I will take her out for a test run.

Cheers!

Before anyone chimes in about "running on the centre-stand" that bike has chopped monoblocs (both carbs fed by the LH float bowl) meaning it won't run safely on the side stand. That's why Norton did not fit a side stand to those bikes.
My '64 650ss is the same.
Cheers