[supercrouton]

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.

Symptoms:
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...

 

[Loffer]

Good tip Dan , ill have to remember that one.

 

[hillbillyhell]

I'll have to get all these Lucas mags out of the drawer where I throw them to see if that stud is loose! hahaha

Good tip, that's one of those things that could drive a guy nuts.

Clay Rathburn; Too American for Lucas Products since June 7 1974.

 

[Ducbsa]

That would make sense, since i think you can use an ordinary points type test light to see when the points open if you remove the screw and depend on the taper to keep the assembly in place. This is for static timing only, of course.

 

[supercrouton]

Yep. it's often the intermittent problems that are the toughest ones to solve, and this one was pretty random. BTW, since you are too American for those Lucas mags, you can ship 'em all to me. It's my way of helping you maintain your high level of American-ness You're welcome!

I'll have to get all these Lucas mags out of the drawer where I throw them to see if that stud is loose! hahaha

Good tip, that's one of those things that could drive a guy nuts.

Clay Rathburn; Too American for Lucas Products since June 7 1974.

 

[Tony the torch]

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.

 

[supercrouton]

Thanks Tony! That makes perfect sense.

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.

 

[Mr.Pete]

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.

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.

 

[Ducbsa]

Do you mean that you wedge a shim between the OD of the cam ring and the bore it fits in?

 

[Mr.Pete]

Do you mean that you wedge a shim between the OD of the cam ring and the bore it fits in?

No,don't try to shim the OD of the cam ring.
Put the shim into the faces between the cam housing and main body.It will tip the cam ring slightly on an angle (or straighten it up,if it was at an angle).If you put the shim near the cam lobe with less point-gap,the gap will increase and the timing changes.

 

[Ducbsa]

That's an interesting approach.

 

[mad dog mike]

This past year I have been pulling my hair out trying to get my 1958 TR650 back on the road. I had made a big mistake letting the bike sit for a couple of years since I was riding my Harley all the time another story back to the K2F mag problem. I finished having the valves ground down and the jug milled due to the head gasket blowing between cylinders and I installed a new carb. After reassembly of the engine the bike was back firing out the exhaust, thinking I had a timing issue I proceeded to re-time the mag. I found that the bike would start right up 1st or 2nd kick but after running for a bit it would start back firing upon acceleration. I was then thinking that the K2F mag had to be the issue even though it appeared I was getting really good spark. I removed the mag and set it up the my bench and using a drill was able to spin it to check the spark of each plug. They both where firing with a very nice blue spark, confused at this point I removed the points cover performed the same test and I noticed that the points where firing twice but 180 degree apart. I replaced the capacitor with a new product EasyCap Retested and found the points only firing once during rotation. The Bike is running like new. Hope this helps any ? drop me a note. Cheers Mike

 

[supercrouton]

Yep, the product mentioned above definitely works. See this thread for more info on the EasyCap

 

[Quaffmeister]

A buddy of mine rebuilds mags as a bit of a sideline, he's had a lot of trouble lately with repop pickups made in India.
First off the brush carbon is too soft and leaves a bad case of skid marks on the slip ring. Secondly and a little harder to spot is cracks in the pick up body, starts and runs fine, only breaks down when it's hot.
Just because it's new don't mean it's good any more.

Joseph Lucas, keepin' motorcyclists guessing since 1902​

 

[Tommo]

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 degree....am 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.

 

[Tony the torch]

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 degree....am 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

 

[Tony the torch]

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

 

[Tony the torch]

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.