we have lift off….

buy not at the first attempt unfortunately.

I tried the trick of adding a little petrol down the spark plug hole and a got very short run at the second attempt, then nothing.

Then I tried trick number two and heated an old spark plug as this helps the engine to fire. But to no avail again.

So I reduced the contact breaker gap to try that… and nothing happened.

So I made the gap bigger at the recommended max of 0.018″… and again nothing happened, not a cough or a putt or even a back-fire!

So I tried raising needle in the carburetor, to increase the fuel to air ratio as it did fire with fuel down the plug. But you guessed it – still dead.

In desperation, I then lowered the needle to weaken the mixture, not expecting it to work, and it didn’t!

On the verge of giving up , I checked the spark and it was very weak. There was an intermittent spark on a plug held against the cylinder head. However, a better test is to see how far the spark will jump, as distance is proportional to voltage. A good spark will jump 3/16″ in old units or approx 4 mm. The best I could get was less than 1 mm, so the plug sparked when out of the engine, as the plug gap is 0.5 mm, but would not spark under compression pressure in the engine as the magneto output is too low. Progress, as at least I know why it won’t start; now I need to find the cause so off with the flywheel.

The only thing I noticed was the the Woodruff key was partially sheared. I figure this has happened as the flywheel is not a very good fit on the crankshaft taper and it rocks a little. The purpose of the key is to align the flywheel with the stator coils to get maximum magnetic flux at the point the contact breaker opens. The taper on the shaft is intended to do the rotational driving of the flywheel. However, on this engine, the taper is not mating correctly the key has to do the driving and it’s too weak to take it; hence the partial shear. I doubt this is the cause (wrongly) but make a new key from a suitable washer, as a temporary fix.

By now, I’m lacking confidence it will ever start, so I use my final trick of heating the cylinder head with the spark plug fitted, using a heat gun.

and the results are in the link below:

So the partially sheared Woodruff key was the root cause.

I just need to get it running better now, as I can’t rely on a heat gun to start it when doing Lejog  (Scotland doesn’t have electricity – does it?)

Oh, and I’ll explain “Lejog” another day.

 

 

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