I have a 2001 model honda 100cc motorcycle. My problem is that the engine is somehow noisy maybe because of 8~9 years running. What do I need to do to solve it, do I need engine overhauling?

'year make model' in all questions please!
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It depends if it is a four stroke or a two stroke engine? Two stroke exhausts are tuned to provide back pressure to push any unburnt fuel back into the combustion chamber. Four stroke exhausts are just a muffler.

You will also need to change the carburetor.

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You should get nothing to the engine if the kill switch is in the no run position. It sounds to me like you are saying the starter is running but not engaging with the engine. This condition is typically the result of (a) low battery (b) weak spring on the starter. First thing to check is the voltage at the battery, start solenoid and then the starter. If voltage is good ... 11 or more volts, suspect the starter.
How old is the battery, BTW? Original? Batteries are typically good for up to 5 years ... let me repeat ... UP TO five years. Check all connections for tightness and that are all clean.

Hope this helps.

The Honda CRF100F 2003-2005 has a 100cc engine and uses a spark plug gap of .7 mm.

The Honda CRF70F 2003-2005 has a 70cc engine and uses a spark plug gap of .7 mm.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Quote your frame number to your local Yamaha dealer they will have the search data you need

Hi. What you are notice from your scooter is just a normal noise of the scooter because on the first start of the engine it is cold, when its getting hot the noise will gone. So before you run your scooter have engine exercise first as warm up. Also you need to change your engine oil because you already reach the 500km.

Hi. What you are notice from your scooter is just a normal noise of the scooter because on the first start of the engine it is cold, when its getting hot the noise will gone. So before you run your scooter have engine exercise first as warm up. Also you need to change your engine oil because you already reach the 500km.

Hi, Flaxman_spoo and the usual suspects are:
1. Dirty or clogged air filter.
2. Faulty spark plug.
3. Bad Gas.
4. Improper oil level.
5. Improper chain adjustment and lubrication.
6. Low tire pressure.
7. Dirty or contaminated carburetor needs cleaning and tuning.
8. Broken carburetor spring.
9. Carburetor spring on backwards.
10. Vacuum leak on carburetor or intake boot.
11. Too much slack in the throttle cable
12. Clogged or faulty fuel pump filter or injectors.
13. Faulty pressure regulator.
14. Improper valve adjustment.
15. Slipping clutch.
16. Improper timing.
17. Low compression.
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I would.