Will run on one cylinder, but not two!

[ttrand]

‘51 plunger Flash. Was having lots of trouble with starting and idling. Found out that I had the wrong carb (also an Amal 276). Throttle slide was worn and so I bit the bullet and bought a new 276 from Burlen. Just installed it but still no dice. When cold, it starts right up, but still wont idle. Starting after this won’t happen until it cools down again. During the plugs in/out, trying various choke/tickle/ throttle position combinations, I got it to start and idle… on one cylinder only! I’d accidentally forgotten to put the plug cap back on one side. As soon as I re-attached the plug cap, neither side would start!

Background: mag produces big fat blue sparks, Ive set the timing very carefully and am sure its good. New plugs, caps, HT leads, I’ve serviced and gapped the points, carb is new with all jets settings at spec. Just done a top-end with new pistons/rings, valve guides etc. 150 PSI compression on both.

I’m at a bit of a loss, and assume that there’s something with the mag I need to figure out. Anyone here point me in the right direction? Cheers all, and happy holidays!

[ellis]

Hi ttrand,

Magnetos can cause this problem. I would have it checked by a magneto specialist.

ELLIS

[CheeserBeezer]

Almost certainly the mag and from your description most probably caused by new, poor quality, pickup brushes. Take the pickups off and replace the brushes with some original Lucas if you get hold of some. Have a look in the pickup window so you can see the slip ring. I use a dentists' mirror or borrow the wife's makeup mirror It has probably got a thick black line round it. Clean the slip ring by wrapping some medium emery around the end of a piece of rubber hose. Press it against the slip ring and kick the bike over repeatedly until the slip ring is clean. Replace pickups and see if that's cured it. You can even use the crappy pickups initially but they will foul your slip ring again within a few miles. I got fed up of telling you-know-who to stop selling these. Some of the magnetos that come in for repair have this problem and nothing else. The pain that these crappy pickups cause is criminal.

[groily]

The pain that these crappy pickups cause is criminal.

Too darn true, too darn common and, worst of all, constructive complaint has always been met with a wall of total indifference.

[Swarfcut]

   See if it sparks on both sides at the same time, an indication that a conductive track exists around the slip ring. Following CB's plan should eliminate this, as any such track is carbon  from the poor brushes embedded in the surface of the slip ring. A good clean out of the slip ring location with a paper towel worked under the slip ring will also help matters.

 Swarfy.

[Rex]

Remember to put a piece of card or paper (or hold down the cut-out) between the points or you'll get a sharp reminder of what the mag is for..

[ttrand]

Almost certainly the mag and from your description most probably caused by new, poor quality, pickup brushes. Take the pickups off and replace the brushes with some original Lucas if you get hold of some. Have a look in the pickup window so you can see the slip ring. I use a dentists' mirror or borrow the wife's makeup mirror It has probably got a thick black line round it. Clean the slip ring by wrapping some medium emery around the end of a piece of rubber hose. Press it against the slip ring and kick the bike over repeatedly until the slip ring is clean. Replace pickups and see if that's cured it. You can even use the crappy pickups initially but they will foul your slip ring again within a few miles. I got fed up of telling you-know-who to stop selling these. Some of the magnetos that come in for repair have this problem and nothing else. The pain that these crappy pickups cause is criminal.

Cleaned the slip ring (it was filthy) started right up! The pick-ups look very old and I noticed that the slip ring has a section of shiny brass, and the rest looks like ceramic or something similar. It this normal, or is it worn out? BTW Im not sure who "you-know-who" is, and I don't want to buy bad pickups, should I only go with Lucas then?

[Superflash]

In this day and age Lucas is nothing more than a name. If I remember correctly the Lucas brand name was bought out by Wassell and it's been all down hill from there.
If the pickups look fairly old you may be lucky and have originals. If not too worn then keep them.
There are 2 types of slip ring. Ask me how I know... the one you have is for twins, and the ones with brass ring around entire circumference is for single bangers.
HTH
Cheers

[groily]

I don't want to buy bad pickups, should I only go with Lucas then?

Nope. You should get them from one of the accredited magneto people who sell decent UK-made non-leaky ones, and brushes that are OK too. Brushes taken from red 'Lucas' boxes are OK. Brushes sold as part of the deal with a cheapo lightweight pick-up are definitely not. I probably have a hundred 'duds' that folk were conned into buying, it's just theft frankly. The main thing is that the brush shouldn't 'write like a pencil' (after a few strokes to clean off any dust on the tip). If it does, too soft, but will work as an earth brush if need be.
A caveat needs adding though, that good quality 'two-screw fitting' pick-ups for K2FC and later K2Fs aren't available from the preferred UK-made source and haven't been for a good while. This can be a PITA because although the ones from you-know-who are OK cold, quite often a serious 'hot' test shows a huge increase in rpm is required to get good sparks out of them. Ie, they can leak. Got a box of them as well, darn things.

Sliprings also need to come from one of the proper sources - they won't be Lucas either. But if your slipring has cleaned up nicely and there aren't grooves and ridges, if the brass segment is shiny and the rest is clean, you ought to be OK now. You don't want to have to replace that unless you have to. The one you've got will be the right one - which is part # 455361 for a  Lucas anti-clockwise drive twin-cylinder mag with the slipring fitted at the contact-breaker end of the armature. There's another two-cyl version (454497) for clockwise drive for eg Vincents, but if that was in there, it wouldn't work!

(The reason it can be confusing sussing which you need on a given mag is that both the above parts are used on instruments of the opposite rotation where the slipring is fitted at the drive end of the armature. Hence, vendors tend to say 'check what yours looks like before ordering' - or state what exact mag it's for! It is made worse by the fact that on some BTH single cylinder mags, they used sliprings with just a 90ish° brass arc like on twins, although any single (or 4 cyl) mag will be good with a 360° brass track.)

[CheeserBeezer]

If you send me a pm and are prepared to pay by paypal I'll send you some which I know to be OK. I even have some genuine Lucas n.o.s. Glad the fix worked!.... I knew it would... been there, done that a thousand times!!

[bikerjohndavies]

Cleaned the slip ring (it was filthy) started right up! The pick-ups look very old and I noticed that the slip ring has a section of shiny brass, and the rest looks like ceramic or something similar. It this normal, or is it worn out? BTW Im not sure who "you-know-who" is, and I don't want to buy bad pickups, should I only go with Lucas then?

Andrew was referring to the carbon brush with spring that fits into the pick-up that are the problem. Fit a decent set and problem should be fixed.

[CheeserBeezer]

There are quite a few brushes around. The most common ones fall into three categories. Type 1, total crap, can be distinguished (usually) as a component of new, white box, pickups. These brushes have dark grey and polished appearance and, when new, have flat ends. The end where the spring fits is parallel. You can draw with them. They feel smooth when you slide them over paper. Type 2, satisfactory, sold by Wassell as spare brushes, often in boxes of five, and also (usually) as a component of pickups sold by Wassell under the Lucas brand. These brushes are grainy and almost black in appearance and, when new, the ends are rounded. The end where the spring fits is mushroom shaped for the spring to clip into. These brushes have a powdery surface which you can draw with initially but is best rubbed off on paper. They feel rough as they slide over the paper. I've used lots of these and they are OK. Type 3, the best, original Lucas brushes, identifiable by a slot along their length and having long, very light springs. These also have a grey/grainy appearance, not powdery, and you can't draw with them. They are very hard and, if the ends are flat will cut into paper as you drag them across. Even if contaminated with oil it's worth soaking them in a degreaser, cleaning and drying them and abrading the ends as they're probably still better than any you can buy. There is also a 'rogue' brush which pops up occasionally, which is used as a resistor in car distributor caps. It has about 50k ohms resistance when tested along its length so it's always worth checking for continuity from the brush to the end of the spring before reusing old brushes; this also exposes rusty spring contact with the brush. Lesson over!

[JulianS]

These are new old stock real Lucas.