rgrent

I need any and all advice on this one guys.I have a stock 914-6 (1991 cc "T" engine). A couple of years ago on a long trip into Missouri, the engine started popping and backfiring substantially. I managed to nurse the car back home to Canada with the help of Octane booster and replacement plugs and points. Since then, I have replaced everything I can think of which may cause the problem: carburetors(still exactly the same problem), all carb gaskets, needle valves, complete exhaust system, relays, CD box (I have tried three different units), ignition wires, points, rotor and cap, coil, distributor, plugs (many times with Bosch WR5DPs and NGKs),alternator and regulator. I have removed all of the carb jets and adjusters and ensured they are clean. I have run every type of carb cleaner through the carbs I can think of and run Dextron III transmission fluid through the cylinders to try to clean out any excess carbon. I have set the timing numerous times and adjusted the valves at least twice, once with the engine out of the car. Nothing I have done has made a very significant difference. I did a compression check (not sure I did it correctly) and got readings on all of the cylinders between 100 and 118 PSI. I suspect that I should have held the throttle open while cranking the engine (any feedback is welcome). I am completely at a loss as to what to do next. Help!