So, you are a biker enthusiast or DIY mechanic or a kid learning to drive around with your parent’s motorcycles. Welcome to the fantastic world of bikes! This simple and easy 2 step guide is put together to help you with tuning your motorcycle engine to achieve the maximum power delivery and the best fuel economy. This guide is primarily for two-stroke and four-stroke carburetor type engines and not the FI types like Kawasaki Ninja 400. But you are welcome to read on and get to know the old-school method of engine tuning.
Let’s go through the motorcycle basics again
By now, you would have noticed that the bike has an Engine and has a carburetor attached to it. Check your engine entirely and see if there are any oil leaks, damaged cylinder heads, weird noises, etc. If there are any of these issues, stop here. Get it fixed and then come back to this guide.
Now we assume that your engine is live and in good condition. If your bike is brand new, then ensure to clock at least 2000Km or 1200 Miles on it for “running-in” your engine. Post which, get the engine oil replaced. This check is vital for your motorcycle engine’s life. After this, fill up your tank with your usual grade of Petrol or Gasoline. The engine will need a retune if there is a drastic change in fuel grade. Finally, check your motorcycle’s air filter. Clean or replace it, if necessary.
Ride your Motorcycle to warm the engine before tune up
Take your motorcycle out for a ride around the town. Ride around at a decent speed for at least 10 to 15 minutes. Doing this will warm up the engine, and the lubricants will flow more smoothly through your engine assembly. Once done, mount your bike on a center or a paddock stand. If you have neither, a side-stand would be fine as well.
Let’s get started on the Engine Tune-Up
Step 1 – Identify the air/fuel mixture screw location on the carburetor
There might be two, depending on the carburetor. One of these is “Idle Speed” Screw, which is attached to your throttle – to control the idle speed of the engine when the throttle is released. We will get to that later. The other screw controls the air/fuel mix ratio for the engine. Usually, this screw will be of golden color (at least in cases of Mikuni brand carbs).
Now for your motorcycle die-hards, this screw would be an Air-screw for a two-stroke engine and a fuel-screw for a four-stroke engine. The primary difference: Fuel screw, when turned in (clockwise) gives an Air-Fuel lean mix and turned out (anti-clockwise) to provide a rich mix. Likewise, Airscrew, when turned in gives a rich Air-Fuel mix and turned out (anti-clockwise) to give a lean mix. DO NOT FORGET THIS.
The Lean mix means more air and less fuel enters into the engine, whereas the Rich mix means more fuel and less air enters into the engine. DO NOT FORGET THIS EITHER.
Step 2 – Turning the screws for the ideal mix ratio
Remember the “Idle Speed” screw mentioned earlier? Turn the screw clockwise, so that the engine RPM touches 3000rpm on the tacho. Now gradually, turn the air/fuel screw to get the leanest mix as possible. As you do this, you would notice the engine RPM reducing as well; this is normal. While you make the mix leaner, ensure that the motorcycle engine does not stall, by turning the idle speed screw for higher RPM.
Once you are at the leanest air-fuel, mix, you can notice the engine RPM fluctuating with the tacho needle swinging. At this moment, start turning the screw for a richer mix, 1/8th of a turn at a time. As you do this, the engine speed will become more and more stable and steady. When you are about 3-4 turns done, the engine RPM would have become constant. It is at this point; you stop turning the screw. This mix is the ideal “Air-Fuel” mix stage.
Post that, start turning your “Idle Speed” screw anti-clockwise to get the engine speed back to around 700 to 1000 RPM. Now, give the throttle a quick twist. The engine response should be crisp and fast without any stall or hiccups. Turn the motorcycle off and then try to start it again. The engine MUST start in a single kick or self-start without much trouble. If there are no issues till now, and your engine is sounding smoother with better throttle response – Congrats, you’ve completed the tune-up of your motorcycle engine!
Final check on the tune-up
After any change or modification to your motorcycle, its good to go for a ride, feel the engine performance in all gears at all speeds. Depending on the feel, you can go for minor re-tune of your motorcycle engine. It is okay to do it over a couple of times before you get to that sweet spot. Also, try to figure out the fuel mileage change.
Frequently Asked Questions (Section For Newbies)
The engine dies while tuning
Set the idle speed screw for a higher Engine RPM speed and then try to start tuning again.
The engine response is weak at higher gears and the pick-up is weak
This could be due to a lean air-fuel mix. Try to make it a little rich, again 1/8th of a turn at a time.
Engine heats up too much
The mix is either too lean or too rich. Try to make it richer or leaner this time.
Whenever I give the engine a quick throttle, the rpm increases fast but comes down to idle speed very slow
The mix is not optimal, probably towards the leaner side. Try adjusting to make it a bit richer.
Too much low-end torque and the engine sound is very Beaty/thumpy.
You must be a facing a mileage drop as well, especially at low-speed cruises. The tune-up is on a richer side. Make it leaner and your problem should be fixed.
Gear Up and Enjoy your ride
When the above steps are done and settled, Gear Up and go out for awesome rides. If you’re happy with the tune-up or facing any issues, do let us know in the below comment section and we’ll help you out!
While we are avid fans of long motorcycle trips ourselves, we recommend you to stay at home during these troubling Corona / Covid19 times. Practice Social Distancing to keep you and your loved ones safe!