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Sounds like you need a valve adjustment, if it is popping thru the carb, the intake valve is open at the wrong time, this can be caused by three things, too much gas, timing is wrong (stretched chain) or valves too tight not allowing valve to close. I would adjust valves first.
Have a trained tech service and properly jet the carb and set idle and idle mixture.
If you have spark, compression, and the valves are adjusted properly the only thing left is the carb. The FCR carb is as complex as the entire engine!
This can be attributed to numerous issues, popping through the carb can indicate timing issues, valves out of adjustment, or a number of other things. Bad gas in the carb could also be a part of it, did you replace the fuel filter? Also, make sure you set the gap on your plug correctly and that you replaced the plug with the correct replacement plug.
Basic setting for idle adjustments is ~1-1/2 to 2 turns CCW from CW stop. New stock (paper) air filters don't require re-jetting--only K&N foam replacements require one size bigger main jet. Adjust each carburetor idle screw for smoothest idle. Each screw should be about the same adjustment--if one is non-responsive, that carburetor may need internal cleaning. Make sure you have good spark plugs and the ignition points are clean and set to proper clearance. The ignition coils on these old Honda's were typically weak--try to find a modern replacement. The carburetor slide needles should have the 'C' clips in the center groove. Make sure the retainers are down tight. Check the engine valve clearances (about 0.003 " cold) for both valves when the crankshaft is set for TDC when that cylinder is coming up on compression.