S4 REV doesn't go up

[mchou83]

Dear all
I had a S4 a year ago, recently I ran into a engine REV issue. When I normal riding in 1-4 gears, the throttle turn smoothly, but the RPM can only go up to 4000-5000 then stay there, can not go up higher. Unless I ease the throttle a bit, then it will go higher then before.
The video I took is in station. It's the same situation when i riding. Video @ the 15's I turn the throttle, the RPM can only goes to 3000 then goes down, but my hand still turning the throttle.

Anyone can identified the issue? my local shop can not help alot with this problem...
sorry need to here, don't know how to embed a youtube video yet, please click the following link
https://youtu.be/ORnOEj5hOdM

Many thanks

[ducpainter]

When was the last time the bike was serviced? New plugs...valves adjusted...fuel filter...belts?

It sounds, to me anyway, like it's running on one cylinder then the second cylinder cuts in, but it's hard to tell.

[mchou83]

Last big service was 1000km from now, checked the spark plugs, belts.... but not too sure about fuel filter and fuel pump.

[ducpainter]

If the fuel filter hasn't been replaced in the 5-6K miles...8K...start there.

[stopintime]

If the fuel filter hasn't been replaced in the 5-6K miles...8K...start there.

if it simply has a problem getting fuel, also check the overflow tube from the tank (vacume in the tank can hold back fuel)

[mchou83]

alright,,, i will find a time to disassemble the fuel supply unit.. Hope just the fuel pump issue.