Misc: Ignition Mysterious Meteor misfire - what am I missing?

[Bill Thomas]

That sounds like the "D" Distributor Vic, You can still get them on e/bay ,
£100 ish Most spares you can get from a bloke in Devon, UK,
Some from The Spares Company
I got some Bob weights from Devon to change a triumph twin to a Vincent Comet single,
With me grinding one cam lobe off,
And for a Twin, if you fit the Twin spark coil, You can't put the HT leads on wrong,
You don't need a rotor arm.
Thanks to Len Matthews for info.

 

[SteveW]

Several weeks ago I headed out for a ride on my '50 Meteor. The tank was full, the sun was shining and all was right with the world. The bike had been running fine since a rebuild about a year/1000 miles ago.

I was riding at 50-60 mph and, after about 45 miles of riding, the bike started to misfire. At first, just every now and then (at constant throttle). It got progressively worse and I eventually turned around and went home. The bike starts up fine and idles without problem.

It never got so bad that the bike wouldn't make progress - it just surged and bucked. It didn't seem to matter whether I was accelerating or under constant throttle or if I were going 45, 50 or 60 mph (or slower). I opened the filler cap to make sure there was no vacuum and opened both taps. It made no difference. I put in fresh plugs (both NGK B7EVX and Champion N4C) - no difference. When I got home, I replaced the small coil and HT lead for the new type BTH "magneto". I also verified that the ignition timing had not slipped. Also checked valve clearances. All checked out fine. I opened up the kill switch on the handlebar and made sure the connection was good and not shorting to ground.

The carb is a new Premier Amal Mk 1 32mm unit: 0.106 needle jet, 250 main jet, needle clip in the middle groove.

I have not drained and refilled the fuel tank yet since, if bad fuel were the problem, why would it begin to start misfiring after riding for 45 miles on the tank. I've only used non-ethanol fuel in the bike.

I'm running out of ideas for things to check. What am I missing? Anything else the group can suggest? I'm flummoxed...

Thanks in advance for any help you can offer!

Sounds like a problem I had years ago, the mag was failing under increased compresson. Start, run fine until I hit a certain speed then it would sputter, buck, etc. Overhaul the mag and your your problem will go away or at least be isolated.