]Just thinking out loud here, air, fuel and spark are all you need to make an engine run. Lots of air, K&N filters with no obstructions. Fuel, even if the new fuel pump wasn't working and it is, the float bowls are full, I can see it with the jet cover off so there would be enough fuel for a 1/2 min. or so.

Spark, it starts and runs at high rpm, could there be some condition where the spark is less at low rpm or after the key is released?

To see the whole story, http://www.classiczcars.com/forums/help-me/49271-engine-will-only-run-above-4000-rpm-carbs-timing.html#post429569

Thanks, Chris

Get an inline spark checker. I would be surprised if they don't have those at Canadian Tire or Princess Auto.

Where in the GTA are you? I'll probably be up in Scarborough sometime in May.

By the way, just for fun, check the polarity on the coil and make sure you don't have it swapped.