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Lucas K2FC magneto trouble help

9419 Views 17 Replies 9 Participants Last post by  Tony the torch
This is not a call for help, but rather a tech tip that may help you with your K2Fc magneto if you are having trouble with a poor/no run condition. The time this happened to me, it was on a fresh build, complete motor build, complete mag rebuild. And the bike ran like a champ for two weeks before this issue reared its ugly head.

Backfiring out exhaust, stalling out, and eventually a "no-run" condition, only occasional firing of either cylinder. It was much like having very fouled plugs, and having the kill switch "on".

Upon further trouble shooting, it began to run, but only with the cap off (even without the kill wire connected).

The issue turned out to be a slightly loose (not rattling loose, just not completely cranked down) center stud. After tightening the stud, it ran like a champ again, instantly.

I hope this info helps another one of us fools who are addicted to old British iron.

Cheers, Dan.

This is not the mag in question, but it is a K2FC...
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More magneto tips....
On all mags (Hunt, Lucas or BT&H) we use a buzz box to set the static timing for an initial setting point, but we always check that static timing setting by clamping the spark plugs to the cylinder fins and kicking the engine over with the timing light pointed to a degree wheel.
make sure you have the advance unit locked in full advance,
If you don't verify where where it's firing this way at you are just assuming the timing is ok.

Many times on Lucas mags you will get a different firing point and point gap on each cylinder and it is necessary to "tap" that center bolt sideways to correct the centering point and thus correcting the gap and each firing point.
I've had a go at doing this with a strobe,and found I had to kick the engine over pretty fast to get the strobe to light up and so was not able to view the timing disc properly.I was able to see it was firing somewhere in the right area,but couldn't tell what I missing something?
I've been thinking about trying to make a set up for the primary side and strobe with the engine running,but don't really like the thought of primary chains and sprockets getting caught up with strobe cables.
what we do is put a strip of yellow pin stripe tape at the 38 degree mark so you don't have to read the numbers just look for the yellow line
you guys realize while timing a magneto that many strobe timing lights will light up fine on one cylinder and not on the other because they have a sensor diode in the pick-up clip that needs to be flipped over or reversed.
this is because single fire magnetos fire each plug in a different A/C polarity so if you aren't getting a flash try flipping the pick-up clip over
Tapping the centrebolt will only change the radius of the points heel,and it will make the same change on both cam lobes.The gap will increase or decrease the same amount on both lobes.
It will not correct any differences in points gap or timing.
You need to move the cam lobes to correct timing difference.The easiest way is fit a shim on one side,between the cam housing and main body.Even a 0.003" shim can make a big change to timing differences.
you're right Pete,
I had a brain fart, that only works on the unit points ignition.
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