Honda Dio sounds like a KTM bike after the owner performs DIY service

The silent Honda scooter noise is accompanied by a throaty growl when the throttle is opened. This sound was not present before my DIY adventure.

BHPian NiInJa recently shared this with other enthusiasts.

Hello all, hope everyone's doing well.

I have a Honda Dio 2013 model that has been passed onto me by my brother who shifted abroad and it has been my toy ever since. For the last two/two and half years it has been running on and off, lying idle for months at length due to Covid and WFH. The scooter used to start after a few dozens of kicks with choke on and once operational, it would start with the electric starter as well. It was working fine for running errands but felt underpowered, had a few misfires once or twice when starting (a big explosion resembling a gunshot from the silencer) or some petrol overflowing (flooding?) from the pipe attached to the carburettor when kick-starting after a long time.

Recently, I developed an itch to do a DIY service on the scooter, just to see what's happening beneath the plastic body. Also, my wife yelling at me to start the bloody scooter so she could drop my kid to offline school is another reason.

So, here's what was replaced:

• Engine oil (HP 10W30)
• Gear oil (Castrol 80W90)
• Spark Plug (NGK)
• Air Filter (Local, could not get genuine Honda part nearby)
• Secondary filter (simple sponge, again not genuine Honda)

The service was uneventful. The air filter was clogged - no wonder the scooter felt underpowered, the spark plug had turned black and the gap had widened to the point that I heard the spark plug thanking me for removing it. And both the oils, well, let's just say I haven't seen any oil as dark like this. It was like soya sauce mixed in clear soup. I was surprised the scooter was still running.

Anyway, after changing everything mentioned above, the scooter became much, much smoother and the wheezing was gone. It can now pull easily up to 60 kmph or pull up an incline with two on-board. The only problem it now has is that the scooter now sounds like a KTM bike (honestly, I sort of enjoy that sound). The silent Honda scooter noise is accompanied by a throaty growl when the throttle is opened. This sound was not present before my DIY adventure.

I had a similar problem with my R15 when the service guy said there was a tear in the rubber pipe that connects the air filter with the intake mechanism. So my first check was to see if there are any cracks or a torn pipe on the intake side.

I have not opened any piping on the intake side, just the air-filter cover from the outer side. I've rechecked if there are any torn pipes but couldn't find any. Even went a step further and tightened the screws connecting those pipes. The carburettor was untouched as well. In fact, I removed both the filters, visibly checked for any torn paper folds, and fixed them again but nothing changed. One thing I wanted to try is to fit the old dirty air filter again but our society's janitors disposed it so couldn't retrieve it.

I don't want to take the scooter to a service center yet. It is running perfectly fine, much better than before save for the KTM noise. Any inputs to resolve this are welcome!

Some notes

• The engine head is wet with oil, possibly due to the misfires but it has not resulted in an alarming oil leak.
• Same with the carburettor, the lower part of the carb is moist with petrol but is not leaking petrol now.
• I don't have any service history of the scooter. The only history I know is that it was not serviced for a long long time.

Here's what BHPian ashishsGT had to say about the matter:

My suspect would be the air filter itself. Most of these local filters use subpar media, which can also have a bearing on the induction note. Since the growl is mostly associated with opening the throttle wide, I'm guessing this could be it. Try replacing it with an OE grade filter and see if it subsides. Just my two cents. Hope it helps.

Here's what BHPian supremeBaleno had to say about the matter:

Possibly due to one of the 2 filters that were replaced?

Any rust/holes in the exhaust pipe/assembly?

BTW, I understand air-filter, but what is the second filter in a bike?

Here's what BHPian audioholic had to say about the matter:

I guess this is with the air filter itself and its seating inside the airbox. When there is a leak in the airbox the scooter will get that growl of the KTM. First, replace the air filter with a genuine Honda one which you can buy in any Honda ASC off the shelf, and if this noise still persists, check the hose that goes into the intake from the airbox. There might be a leakage in this joint as well.

If this is all clear, then the secondary air filter has a vacuum hose that switches the valve on or off. I had this issue where the valve itself would make a clattery noise and then allow secondary air to be supplied even when there was no vacuum, i.e, even while accelerating while it should only be activated when the throttle is closed and there is enough vacuum in the manifold.

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