AVB, Grumpy, Funzo and ODK members,
Here are a few pics of the difference between the earlier and the late model jet setups on the pulsa prime carby's.
The first pic shows the later model one with the jet removed on the left, notice how the hole is much larger.
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And here's the jet.
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Last pic with the jet fitted.
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Funzo, the jet goes in with the tapered side going into the tube.
I'm still not convinced the carby is not the reason it's not starting although it doesn't eliminate the fact there may be a problem with it.
If you prime the carb, and you have spark, the motor should run for a second or so at the very least. I think a new plug would also be a good starting point. Just because it generates spark at atmospheric pressure, i.e. outside of the engine, doesn't necessarily mean it generates a spark under compression.