How to 'Kill' a Lucas KVF Magneto?

[passenger0_0]

Thanks Greg. I'll look into these potential issues. It looks like this mag has a brass bodied points assembly and strangely enough the bike does occasionally hiccup on the open road but I put this down to it's high mileage. Maybe there's something else at play as you suggest? I'll report back my findings.

 

[passenger0_0]

I've been for a ride since I've improved the internal earth connection of the kill button (horn button) to give better contact. With nothing else done it now kills the engine on two cylinders at idle but only one cylinder when cruising at 70 mph. Let's hope my throttle doesn't jam open anytime soon!

I might have to talk to a magneto specialist. ....

 

[Martyn Goodwin]

Thanks for your replies so far.

I've checked the continuity of the kill button and it definitely has no resistance as I had wired in a separate earth wire from the switch to a shared ground to get over the painted handle bar.

Interesting point about the 'cheap' magneto end cap potentially being the problem as I was very unhappy with the quality of the rebuild previously done.

Please keep making suggestions as I don't want to use the valve lifter more than I have to.

Why are you worried about the valve lifter? Remember every Vincent that left the factory was fitted with one and it was intended to be used to help in both starting and stopping the motor. Ignition/magneto cutouts were NOT a factory fitment. If your lifter is set up and used correctly it should not cause any issues.

I have covered over 80,000 miles on my Comet since I became custodian and have always used the valve lifter without any problems at all

Of course if you regularly use the valve lifter to stop the motor from high revs it won't last long - it should only be used to stop an idling motor except in an emergency.

 

[passenger0_0]

Good point.
I suppose I'm worried about the stories of the rollers contacting the exhaust followers coming loose. I didn't put this engine together so I don't know what's in there.

 

[Martyn Goodwin]

Good point.
I suppose I'm worried about the stories of the rollers contacting the exhaust followers coming loose. I didn't put this engine together so I don't know what's in there.

All sorts of things can go awry/fail if they are not assembled or maintained as intended. Correctly set up , the Valve Lifter roller should ONLY contact the lifter when you squeeze (not jurk) the handlebar lever.

 

[passenger0_0]

Well - finally an update.

I purchased a Wassell replacement kill-wire end-cap for the magneto and comparing it to the one fitted during the magneto overhaul it immediately became apparent that the centre carbon brush was much longer and had a much stiffer bronze 'spring' element. It certainly contacts the points centre nut now with some noticeable force.

Anyway - pressing the kill button now with the Wassell end-cap fitted kills both cylinders so problem solved. Now I've just got to sort out those worn out (original? - 72 year old) carbs for the upcoming NZ rally and I'll be all set to go.

Thank you all for your helpful suggestions.

 

[greg brillus]

I've found the best and easiest way is to buy new 276 carbs, cheaper than shadow carb's and work well pretty much straight out of the box.

 

[passenger0_0]

I've found the best and easiest way is to buy new 276 carbs, cheaper than shadow carb's and work well pretty much straight out of the box.

You're absolutely right here Greg. I've been reluctant to replace these as they've got brass bodies. Bike needs two right-hand carbs being an early Series B. I've got a coupe of NOS pre-war Zinc 76 carb bodies and brass slides I'm going to use in the short term while I'm saving up for complete new assemblies.

 

[greg brillus]

I have seen oversize slides about 0.030" larger than stock which fixes them up nice. But new slides are about 35 plus pounds on their own, plus machining and other new parts, starts to add up. I know years ago everyone use to fit Mk 1 or 2 Concentrics or Mikuni's which work well, but none ever look as good as the original side bowl carb's. Cheers...............Greg.

 

[passenger0_0]

All good points Greg and I'm a fan of the 276 carbs. My brass bodied cards were chrome plated sometime in the distant past which I think caused both jet blocks to become a loose fit and leak around the pilot fuel/air bleed hole. This is causing poor slow speed running and difficulty starting..