Ok, apart from what makes you as a horse. When the vehicle is parked with the engine on, pull explosions like the ones it makes when walking through the exhaust tube? You mentioned in your post that the compression was bumping; Would you mean what your mechanic did a compression test?
Your failure can be reduced to only these causes; Air input, gas problem, electrical problem, and mechanical problem related to the time chain if your vehicle brings that system (if it is of Correa, this option is elected).
I advise you to do a elimination process. You start with the easiest and cheaper and work towards the most difficult and expensive. Your mechanic was already part of cleaning carburetor, filter, and spark plugs (ask here, you teach your mechanic in which condition came the previous spark plugs?).
Tell him to check if the engine has air input, and replace the distributor and cable layer and rotor; You have not done this and it is basic engine maintenance. Bad electricity conductivity affects the type of spark that spark plugs produce and can cause detonation which could give you explosions too.
Finally, the difficult thing would be to make a compression test and compression leakage test; With this you can get to know if your vehicle has a problem with the time chain, because if your chain is too lazy and needs change, basically the valves of the head are not closing in time when the piston rises to compress the mixed air with fuel and can produce explosions by the exhaust pipe. With that you would eliminate this option.
If your mechanic is of experience, know how to do that; If you do not solve, I advise you to look for a second opinion with another mechanic.
Let me know about your results.
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