RPM bouncing at idle

2014 VFR800 with ~4900 miles (recently sat for 2 years)

I've had this bike less than a week, and am still going through it and getting used to it. After adjusting the throttle cable today I noticed the RPM wasn't holding steady at idle. I hadn't noticed this before, so I assumed maybe the adjustment had something to do with it, so I increased the slack. Problem remained. This happens when the bike is both cold and warmed up.

 

Mine is a sixth gen. I am pretty sure it has reacted in a very similar manner since new when I bought it still in the crate. I am wondering though. I can't see the engine temp on your gauges in that video clip. Is the bike warmed up and at normal running temps when you took the video. If so, I think it is idling a little high. When warmed up, the bike should idle between 1000 = 1200 rpm. Maybe the 8th gen is supposed to idle higher I don't know.

 

The bike was warming up, but hadn't fully cooled from an earlier ride this morning. The temp in the clip was in the 115 range. It was in neutral. I'll be paying closer attention now, but I think I remembered it idling closer to 1200 the day before.

 

it's possible (likely) that throttle plates need synching.

 

That idle, around 1,500 RPM, seems high. Have you looked into the owner's manual or service manual to see what the correct idle speed is?

The up-down-up-down movement of the RPMs looks like the ECU making tiny changes to the injector pulse width in reaction to feedback from one or more sensors. If there's no "FI" light showing up to indicate a sensor problem the ECU is just going about its job as per normal.

I'd start by confirming and adjusting (if necessary) the idle speed then see if it still does the bouncy idle.

 

Someone with more knowledge than me can correct me, but I think that little fluctuation you are experiencing is nothing to worry about. Like I said, mine has done that since birth and I have >210,000 km on mine now. Curious though. What happens if you apply slight throttle to it? Like maybe to increase the rpm via throttle by 1 o3 2K? Does it smooth out?

 

Such a tiny fluctuation. Nothing to be concerned with.

 

Yes, I don't see why the throttle plates wouldn't be a possible factor. I'll keep that in mind when I have the occasion to go tearing into things.
This morning there was no slack in the throttle cable... weird, because I fixed that before bed. I fixed it again, and rode to my appointment (this time brought wrenches). When I parked on arrival I had a few minutes to locate and adjust the idle knob. Adjusted to wnl. Bounce remains, but you guys are telling me not to worry, so I'll take your advise for now. Then I noticed the throttle cable was too tight AGAIN. Upon further inspection I realized that when the bars are at left full lock (to engage steering lock), all the slack is taken out of the throttle cable. I suppose the cable could be run incorrectly, but nothing was obvious to me in the parking lot. Another thing to verify once my service manual arrives.

 

It is not unusual for the throttle cable slack to change when swinging the bars through a full arc. As long as at the tightest point there is still a trace of slack (i.e. the throttle doesn't open) then I'd say the slack is correctly set.

 

Good to know, thanks. It caught my attention because my other two bikes didn't have this issue.

 

I’m no expert, but I would say that is not normal and Honda wouldn’t release a bike with idle like that. How come on cars ECU can control it perfectly?

On my 3rd Gen this is caused by either carbs not being in sync or vacuum leak. I would look into syncing throttle plates if that is a thing. Are they not electronic throttle bodies?


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Cool, thanks for the diagram. From what I can see with the fairings on, it looks like the picture.

 

M sorry I k how this is an older thread but I'm hoping there was a resolution.

I'm noticing the same with my 6th gen but I can hear the slightest miss every few seconds. Also the problem persists even adding throttle. If I hold 1/4 or 1/2 with no load I continue to see and hear this. Additionally I'm experiencing power loss up above 5k under load.