Spirit 94 excessive gasoline consumption

I replaced the piston rings a year ago, but the compression remained low. I was told it was due to the type of rings. Even so, the fuel economy was between 7 and 9 kilometers per liter, but now it's 4 to 5. It's not burning oil, and the spark plugs are coming out black and carbonized. I gapped them at A30. I hope you can give me some guidance. Thank you.

Hello, cylinder compression depends 1) on the seal between the piston rings and the cylinder, and 2) on the valve closure. In the first case, there is oil consumption, fuel consumption, low power, and primarily cold-start problems. In the second case, low compression results in low power, difficult starting, and excessive fuel consumption. In both cases, the spark plug will come out black with carbon deposits from the excessive fuel consumption. Conclusion: No engine can achieve perfect combustion with low compression; the performance is "poor." We speak of good performance when an engine consumes fuel proportionally to the power it produces.
Regards.

Thanks for the reply. Once I injected 10 ml of oil into each cylinder, and it increased the compression, giving me a fuel economy of 7-9 km/L. But the strange thing is, there's no oil leak, and based on your tips, it all seems like a valve leak. It starts well, the acceleration is slow, but once up to speed, it has good power. If I were to have the engine overhauled, would it be better to replace it with flat-top pistons since it currently has convex ones (from the turbo), or would these pistons achieve my goal? Thanks for the replies.