Sil - How large are the holes in the pistons? In order to eliminate compression in the unused cylinders, in theory, the whole piston must be removed. Perhaps the piston holes are small enough to act like a jake brake and require a lot of power to turn.

How about a compression check of the good cylinders. I'd also be interested if you get any readings in the dead cylinders.

How fast does the engine turn when you try start it? Can you measure the RPM with a dwell meter or something like that? I'd like to know what the cranking speed is?

I had a '56 Ford that would start instantly if the battery was up, but not start if it was off at all.

Also - How about running the engine on one carb? Perhaps there is not enough vacume to operate two carbs! You only have half an engine. Try just blocking one of the carb inlets.

When it chugs, does one of the exhaust ports get warm? - if so, the other cylinder is the one that needs attention.

Is there any indication that the dead cylinders are getting any fuel?

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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 415,000 miles put on 9 bricks