Strange Problem

Indeed your timing is fine for CNG but for petrol it is WAY off. As far as your plugs are concerned I'd suggest having them cleaned and then deciding if you wish to stick with petrol or CNG and then have your timing and plug gaps set according to that fuel. This way you can get the maximum performance from the engine & fuel type.

From the pictures it seems your plugs are fine which tells me that your car is set correctly for CNG (due to your timing setup) and that would mean that you use CNG more often.

If you want you car to go faster you should avoid silly things like body-kits or heavy wheel/tire combinations as well as heavy sound-systems. The lighter the car the faster it will accelerate with the same amount of power.

Do note that the plugs and plug wires do next to nothing when compared to stock units (maybe 0.5hp in your case). If you wish to see some decent result (maybe 2 hp) you'll need to fit some form of spark amplification.

Lastly you mentioned that you have opened up your carburetor fuel jets, maybe that sounds great in theory (more fuel + more air=more power) but it does not work that way as you need an optimum ratio in order for the fuel and air to mix and burn efficiently. it's possible that your car is running too rich due to an excessive amount of fuel (petrol) in the combustion process and it would be advisable to either drastically improve the amount of air entering the engine (by giving the car positive intake pressure like a turbo or supercharger or simply by getting the mixture set correctly by a professional.

If you wish to have more performance on petrol then may I suggest la larger carburetor and/or a better flowing exhaust-system.

There are many ways of getting tiny bits of HP from your engine, (which can add up to alot). Such as having your valves replaced and having larger ones fit to your head (ideally with a multi angle grind/face to them in order to ensure good flow and a tight seal. Sadly this type of modification is on openly understood or available in PK at the moment.

Another trick is to have the conterweighted parts of the crank "sharpened" and then having the whole crank balanced so that the sharpened weights don't bash into the oil in the engine but rather cut through it, and the balanced crank will allow you to rev higher without worrying about vibrations etc.

Stiffer valve springs (or dual springs) can be fit along with a more aggressive cam setup so that your car can keep the valves open for longer which will help squeeze every bit of power from the available air/fuel and to prevent "valve float" at high rpms.

Compression could be raised slightly to make the combustion process more violent and therefore produce more power, or it could be lowered alot more to make room for forced induction (like a turbo).

Connecting rods could be lightened & "weighted" to ensure the engine is more stable at high RPMs. or alternatively you could replace the whole rod(s) with I or H beam rods which are ALOT stronger.

I could go on and on and on as in this game these things never stop.