Just a few days ago,My forza 300 goes to about 2000km,but suddently it had a problem with it:the motocycle became hurge vibration between 2800rpm to 4000 rpm.I had checked it and found the problem is caused by the transmission part,maybe the clutch or belt .so anybody could give some suggestion for me ?!! tks!!

btw,my english is so poor!!!

If the vibration comes from the transmission/drive part of your scooter you should check the drive belt with more detail. Check if you can see small cracks on the surface of the drive belt.

It not happens often, but sometimes the drive belt of the Honda Forza 300 has a problem. When your drive belt has small cracks all over the belt it will have more space to move and one of the first indications is vibrations, second is losing power while the engine still revs normal...

At this moment we cannot help you with a Honda Forza 300 service manual, but we can help you with the next best thing… what is the official Honda Forza 300 (NSS300) parts catalog.

You can download the Honda Forza 300 parts catalog in English language here:

- Honda Forza 300 Parts Catalog (English)

Where do you live and ride?

Vibration happens when ridding at a steady speed? Or when accelerating from stopped?

Most low speed transmission vibration on CVT scooters comes from dust in the clutch. If you ride a lot in traffic go for a ride in the country and ride at 100 kph for a few minutes to "blow" out all the dust. Yours looks clean but.

That RPM range seems to suggest the clutch. Take the "bell" off and have a look.

IF the bike has high mileage on very rare occasions one of the weights can get flat-sided and stuck which causes vibration. This disappears when the other weights are forced into balance by the rpm.

^ Maybe the OP can tell if it is a fuel hesitation or a vibration. O2 sensor cannot cause vibration I guess it could cause the bike to run rough but not vibration, which is mechanical. Generally if the O2 sensor fails it defaults to rich, which would result in a black spark plug.

Put the bike on the stand an slowly increase the rpm until the vibration starts and then see if it is engine or rear wheel speed or...
Take the CVT cover off and do it again. Is the belt flapping , when the vibration starts? When accelerating or when decelerating?
Do the test again when going for a ride with load on the engine and see. Is it the same as on the stand?

From another forum

Had a very similar problem recently with my Honda Forza (16K on the clock)

Juddering when cold, under load or on an upward incline start.

Took it in to renew the rear tyre last week and asked them to look into the juddering issue?
They removed the clutch plate from the housing, showed me the wear on the pads (still within tolerances) and explained the dust accumulation would be the culprit.

They cleaned out the housing and now its as responsive as new. Juddering gone.

Oil and clutches don't go together.
If all you did was apply a little oil to the pivots etc. you are probably OK. You will be able to tell by looking at the linings.

Your increased fuel consumption could be because you are riding faster now the vibrations are gone.

If you want to clean the clutch and If you can find some brake cleaner aerosol you should be able to clean most of it. Concentrate on the clutch pads/linings. The drum and other bits can be cleaned with petrol then given a little spray.