At what period of time parts like chain, spark plug, battery, airfilter , brake shoes etc., need to be changed in order to get proper mileage and pickup. problem: my motorcylce gives around 45km/ltr. are there any tips to be followed in order to get better mileage and instant pickup

An engine needs three things to run..fuel, spark, and compression. These also have to happen in the right order, but with you having the timing chain changed you should be able to mark this one off. You need to make sure your have spark at the plugs and have fuel proper fuel pressure at the fuel rail and that the injectors are metering. And you also need compression.

Check tyre pressures . check brakes for drag . check wheel bearings for play . get the fuel map checked also spark plugs and timing
Main thing drain oil and check for extra metal in it
Airfilter may also be dirty
Change your riding style to a more economical style

Many things can cause excessive fuel consumption. First, make sure that none of the brakes or transmission is dragging, or that the transmission is shifting properly. We had a car in the shop recently that had poor fuel mileage and one of the front calipers was dragging against the rotor. (also check the parking brake). Next, is everything up to tune? Good spark plugs, clean airfilter, good PVC, good Oxygen sensors, check for codes, etc. Check if there is a vacuum leak - (use a vacuum gauge). Lastly, if you have access to one, use a emission tester in the exhaust to see what the levels of hydrocarbons are. This will at least tell you if the engine is running clean. Sometimes poor fuel mileage might be a combination of things which all add up, like under-inflated tires, spark plugs fouled, parking brake slightly dragging and poor driving habits. I can always tell the customers who get poor fuel mileage by how often they need new brakes. Someone who lets the car coast and isn't on the brakes much usually gets much better mileage. Those who speed right up to a red light and then jam on the brakes at the last second usually have at least 20% worse mileage.

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Depends what it needs, what problems it has. If no problems oil change for engine and trans primary, oil filter, air filter and spark plugs are likely all you would need. Depending on mileage you could/should find out what inspection is due, if any and do what is on the inspection sheets. If you have laced wheels check the spoke tension and drive belt and primary chain tension/deflection/ check the brake pads, rotors for wear etc and if the brake fluid has not been changed for some time you may want to flush the systems even though it is DOT 5 fluid which is not hygroscopic. Check air pressures, lights, horn etc etc

are the spark plugs gap set to manufacturer specs?

Follow your owners manaul, it has all the services needed according to mileage, of course if you havent been following the book, it doesnt do much good, and you are overdue for Coolant, Trans fluid/ filter, belts, filters, ect. Your car should have a timing chain.

hi you dont say how many miles the bike has done, the normal things to replace are oil, oil filter, air filter and spark plugs, you may want to check all wearable items like chain and sprockets, brake pads, brake fluid change front and rear, poss fork oil change, heck tyre condition, steering head bearings , lubricate all moving parts including chain, cables, footrests, etc, most time consuming part changing the spark plugs no1 and no 4 plugs require removal of engine mount, suport engine as it can move just enough to make refiting the bolts arkward

for mis firing case, need to check the valve timing by aligning the O mark in the cam shaft sprocket and T mark in the rotating magnet, and for the mileage there are several reasons, pls have a check on below things, 1. dont change the fuel station. 2. allways find a good fuel station and have a regular filling. 3. check the airfilter and clean if required. 4. check tyre pressures every 5 days. 5. check chain play is with in spec and also have proper lubrication. 6. check both brake if it is having regular contact with wheel even not holding conditions, 7. check any dust entry in carburretor. 8. Tune the carburretor. 9. check idling RPM is running 750 almost. 10. check tappet valve in right postion. 11. check engine oil condition and quantity. 12. check clutch cable condition and adjust if required. 13. check the mileage test by maintaining reserve to reserve ratio.

When you hear some tapping, that's why you need -valve adjustments. At 137,000miles you probably need more than that to continue your trouble-free drives.

Your vehicle is equipped with a timing chain. There is no periodic maintenance schedule fr the timing chain.
If your spark plugs have never been changed, now might be a perfect opportunity to change them. Ensure that you properly gap the plugs before installation. You will find gap specs on the engine information tag/sticker under the hood.