Starting and running a 1947 16h

A few mins running static? A little way down the road? Or directly after starting?   Air lock in fuel tank, fuel flow restriction, electrical breakdown due to vibration or heat? Will it restart directly after failure? Plug, points, kill switch shorting? Contaminated fuel/ fuel lines.

Bit more background and someone will have the answer for you :)

J  

If it fires and fails... have you removed the jet block from the carburettor and made sure the pilot circuit air passages are all clear?

When it conks out next time, whip the plug out and check for a spark, could be the mag breaking down   

Spark length is dependant on pressure. So a screwed out plug can give a spark but the higher pressure in the engine needs more voltage to get a spark. I somewhere read that a 1/4" gap shall give a spark in free air for a healthy magnet at kicking speed. More on high compression engines.

Though never experienced it myself, it is quite common that old magnetos fails when warm. Check for carbon residue inside the pickup. If breaker points are clean and not pitted and have correct gap, the condenser is often the culprit. Other problems exists too.

I remember when I was a teenager running a CB125S, a friend having an RS125 which did exactly this, it would run a mile then conk out, good spark, plenty of fuel in tank etc, after checking it would do another mile, then repeat.

Of course it was the breather hole blocked in the tank filler, with polish etc.

Sounds like it needs more fuel. Though sending all notes with the 16H I sold years ago, I think I had to go up one step in main jet size from factory specs.

I've always understood that magnetos should have a 15thou  plug gap. 25thou is for coil/points.

Hair spray sound a bit drastic, all that varnish going in to your engine!

Dear Al,

Please could you expand on your understanding that magnetos require a 0.015 gap at the spark plug and coil/points 0.025?  One of my friends has a contact in racing who used 0.001 with reasonable results, the theory being that the magneto has to do a lot of work to get the spark to jump across a wider gap.  

Regards, Colin.

... is a compromise between being small enough for the spark to have enough energy to jump across it and big enough to ensure that when it does there is a decent chance of some mixture being in the gap to catch fire....

I've always used .018" for magnetos. I'd be surprised if a .001" gap would work in a 16H.

A Magneto always has lower HT than coil/points.Hence 15 thou (18thou) plug gap. Coil/points was always aimed at 25Thou. Once you go to electronic ignition as the voltage will be greater you can run a greater gap. RITA was always said to be 30 thou. But let us understand plug gap! For town work, cool running stop starting then a smaller gap until it fouls up which it will do with cool running plugs and dirty mixtures. At which point you need a bigger gap and perhaps a plug that is actually running warmer (to burn off the muck) ie as you would rushing down the motorway. 

My 1940 16H WD was exactly like this when I finally got it together in mid 1990s - looked like a good spark on kicking over, but the engine never ran more than 2 minutes.  It was the original, un-restored 1940 mag of course, warming up and then giving up.  A replacement (not refurbed) 1960s mag has been going ever since.