I am stating the problem below along with relevant details. Need your expert advise to resolve the issue at hand.
Suzuki Margallah with stock G13B Carby Engine Driven 260K KM. No issues with the performance. Maintained on Fully Synthetic 10-40 Oil (suits with better idle and improved mobility experience). Proper regular maintenance at every 5K KM.
Had been using LUCAS 4 TIP plugs and was getting at least 11.5-12 KM/L until May 2014 (sometimes even better).
Car's milage has dropped to 9.5-10.5 KM/L for no apparent reason since last 4 months.
Plugs have been cleaned (seems irrelevant since there is no starting or performance issue any way).
A loose hose pipe (for vaccum) has been replaced on carburator, was making shan-shan noise.
A loose fuel pipe has been replaced.
Fuel system cleaner from STP has been poured.
Carburator cleaner from STP has been poured several times (does improve idle and smoothes the drive). Used once a month any way.
Gear Oil has been changed with Caltex Thuban SAE 90.
Car Alignment has been re done (believe me it does improve the milage of the car - as per my previous experience).
A sympton of some issue that i had been observing is a strong petrol smell (for about 20-30 sec) once there is less fuel in the tank and i turn off the engine. Mechanic says that he couldn't find any blockage in the exhaust of fuel tank.
Haven't seen any improvement in milage it is still between 9.5-10.5 KM/L.
Currently using LUCAS 4 TIP plugs which are in good nick, no issues with starting or idle or acceleration. They are being used for at least 30-40K KMs. Previous Bosch 4 TIP plugs worked 100K KMs without any issue.
Does changing these plugs with NGK platinum (single tip) be of any use and will improve the milage?
Using OEM plug wires came with the car in 1998, should i change these to any good 8 MM or 10 MM wires?
Orignal cylincer came with car Made by Sanki Japan is making small noises like chan chan, should i change it now (since mechanic suggested no need since no apparent issue). I believe if exhaust system is in precise condition it does improve the milage as well.
I will really appreciate your feed back.