Fluttering/rattling Noise From Engine While Under Load At Half-Throttle

[adg44]

I have noticed that my bike makes a rattling noise when I'm at WOT around 5 or 6K rpm before the VTEC changeover. At first I thought it was the airbox flapper, but I fully removed that the other week (literally I tore it out, makes for a very deep engine note) as well as installed a K&N filter. If I stay at WOT for the VTEC changeover, the rattling goes away. The bike also smooths out when VTEC kicks in, so perhaps it's actually something on the motorcycle that is rattling, although I haven't found anything that is loose. It almost sounds a bit like valve clatter, but the noise I'm hearing is slower and not as high pitched as valve clatter usually is.

If I rev the engine in neutral while at a stop, it's completely rattle free. Oil level is good and there is only about 1k miles on the 10w40 synthetic I'm running. Bike has 4,100 miles as of today.

I read through some threads and heard about the cam chain tensioner, but that doesn't fit with what I'm describing. Perhaps this is just a normal sound - I haven't been able to compare it with another VFR.

Any ideas?

- Anthony

[Aeromagic]

Could the engine be pinging under heavy load with WOT and slow engine speed? I'd try a higher octane gas for a tank or two and see if it changes.

[adg44]

Could the engine be pinging under heavy load with WOT and slow engine speed? I'd try a higher octane gas for a tank or two and see if it changes.

Nah, the sound isn't pinging. Also, I had to fill up during my ride, and I was running 93,then refilled with 87 and it acted the same.

[adg44]

OK, I just updated the title of this thread because I rode another 120 miles today and figured a few things out.

1) It only does it at half throttle, regardless what gear I'm in, and whether or not VTEC has kicked in yet.

2) The lower the engine speed, the slower the fluttering. The higher the engine speed, especially when in VTEC, it is much faster and not as apparent.

I think it's either something physically on the bike that is making the noise because of vibration from the engine. At half-throttle the bike vibrates the most, so it's possible. Or after removing the flapper and snorkel from the airbox and installing a K&N filter, I'm flowing a lot more air and it's upsetting the fueling. Given that at WOT and quarter-throttle it doesn't flutter, this is also a possibility.

OR - it's completely normal and I never noticed it before because I always ride with ear plugs. It's only on the last few times I went out that I didn't put in my ear plugs.

Thoughts?

[adg44]

To update this topic again, I spent an hour troubleshooting today. I thought the grounding cable that connects the fuel tank to the frame could be rattling caused by the increased airflow with the flapper removed. I added a washer to each mounting point to secure the cable and keep it from moving. Unfortunately, this didn't work.

I removed the top of the air box, removed the K&N filter (which had leaked a few drops of oil onto the right rear throttle body) and checked to make sure each valve was opening fully when applying the throttle. Everything seemed fine.

I also adjusted the chain (slightly tightened) to ensure that it was at 30mm of slack. This didn't make any difference, either.

I'm out of ideas, so I'm going to continue to work backwards. I'm going to order a new air box and another Honda OEM air filter and install it into the bike. Then if it still makes this rattling noise at half throttle, I can completely rule out any air box mods as the cause. I'm quite perplexed...

[Piperdown]

Hey adg, I've been noticing something that could be similar on mine as well. I haven't put my finger (literally or figuratively) on it either. I've never heard anything but then I almost always wear plugs. It's more of a feel in the pegs or the pants that it's running a little harsh/off. Just like your's it's in the mid-rev range, but it seems better at times than others. Quite strange.

I think this was there before but I had to recently put a stator in so I'm intensely paranoid for the time being in case I screwed up or there is another screw up to deal with related or otherwise. I just don't recall the vibration feeling as noticeable before. Oh well, just going to keep checking things like you are.

The only other thing I could think of was that I might have a bad injector (which is somewhat common I understand) and it's not fueling properly. I used to have a strong gas smell after a ride but that's no longer the case lately so not sure if that's a bad thing and now a worse thing? Who knows.

If I come up with anything, I'll post asap. Wish I could help you but that's all I've got for now.

[Lint]

Hey all, FWIW, I have this with my bike, even when I just picked it up at 6600 miles on it. I think it is a VTEC thing.

[adg44]

Interesting replies. One thing to note is that mine doesn't vibrate or feel like it's running poorly. In fact it is running extremely well and power output is fantastic.

Interesting to hear that someone else has the same issue. Wish we could figure out what is causing it. Is your airbox completely stock?

[Piperdown]

That's the thing. I would probably say it's normal if there wasn't a distinct difference. Like yesterday morning on the ride into work it ran awesome with no vibration whatsoever. Then on the ride home, it had the ol' vibration (or what I perceive it to be anyway) back to the usual.

My air box has K&N and snorkel and flapper deletes. It's been like that for a few years now and the only difference was the sound.

There's another recent topic on leaky injectors so I'm going to have to do some more research on the diagnostics for that.

[NakedViffer]

Since you own a couple boosted cars I assume you are familiar with the sound of detonation? I know you said thats not it, but I'll be damned if what you're describing doesn't sound exactly detonation.

[adg44]

Since you own a couple boosted cars I assume you are familiar with the sound of detonation? I know you said thats not it, but I'll be damned if what you're describing doesn't sound exactly detonation.

I'd be quite surprised if it is detonation. However, I'll run a tank of 93 octane and see if that changes anything.

I'll also then cover up the hole in the top of the airbox from where the flapper module used to sit and see if that makes any difference as well.

[adg44]

I ordered a replacement airbox just so I could put everything back the way it came, and sure enough, at half throttle, it still makes the noise. It's amazing, the minute I move past half throttle, even if it's just 1% more, the noise instantly stops.

When I was riding up and down my alley way behind my house, I was bad and didn't have my helmet on. However, it allowed me to listen to the bike and now this noise sounds more like a squeaking rather than a rattle/fluttering. It goes back to what I thought originally and that something on the bike is making the noise. I spent 30 minutes looking over the bike and I could not find anything that is loose.

Once my phone mount comes in tomorrow, I'll record a video and post it so everyone else can hear the noise as well. I'm all out of ideas now...

[2thdr]

How many miles do you have on your chain? Have you checked it for tight links lately?

[adg44]

How many miles do you have on your chain? Have you checked it for tight links lately?

Bike has 4,300 miles. I just checked the chain and the slack last week, and it seems fine.

[adg44]

I'm going to chalk this up to just a normal noise. The engine is butter smooth and runs flawlessly, so who knows.

[expvet]

I have a similar sound in the same RPM range and found that when it is happening if I pull in the clutch the sound continues, which would suggest it is clutch related. Try it and let me know if the same thing happens to yours.

[PorradaVFR]

I'm surprised I'm the first to mention CCT - I had both go bad (separately) on my former '04 and the sound is certainly "rattling / fluttering" in nature. I too thought it went away under throttle, but I was not considering that the relative noise level was also increasing. Likewise, I perceived clutch in (i.e. throttle off) at lights as a "fix".

I'd suggest looking into the CCTs

[Piperdown]

That's one of the things on my list to check PorradaVFR. I was hoping to leave that for later in the season to check (if nothing else resolves) as I've missed enough of the riding prime time already. I went over some other things on the weekend and nothing yet, so unfortunately the probability is going up. Thanks for your comment.

[PorradaVFR]

That's one of the things on my list to check PorradaVFR. I was hoping to leave that for later in the season to check (if nothing else resolves) as I've missed enough of the riding prime time already. I went over some other things on the weekend and nothing yet, so unfortunately the probability is going up. Thanks for your comment.

No worries. As to the CCT, the noise is irritating but not SUPER likely to create any major issues unless it gets really bad. If the noise isn't causing people to turn their heads and for animals to scatter at your approach I would not think it critical to address it for the time being.

** I am not a mechanic, don't play one on TV, don't assert that my opinion is accurate and urge you to ask your doctor before starting any motorcycling regimen, mileage may vary, results are not guaranteed etc etc etc.

[adg44]

I have a similar sound in the same RPM range and found that when it is happening if I pull in the clutch the sound continues, which would suggest it is clutch related. Try it and let me know if the same thing happens to yours.

How many miles on your bike? And I don't get this through a certain range, it's throughout all RPM as long as I'm not past half throttle. I also noticed that I can faintly hear it in neutral if I rev the engine as well. You may be onto something about this being transmission noise.

[expvet]

I have 3,830 miles. I find that it begins to become loudest near 4,000 RPM. The strange thing is when riding and I hear it if I disengage the clutch and cut the throttle the sound continues. I would describe the sound more as a buzz.

[joemaniaci]

I just noticed this problem just this week.

If I rev up to between 4k-6k rpm in 4th gear or higher and then let off the throttle, I hear this rattling noise. Yet any other time the engine is buttery smooth, cold idle, warm idle, acceleration, etc. I intend to by a mic for my recorder and install it under the tank, because it sounds like it's coming from underneath my tank as well.

[adsrox0r]

I've got exactly the same thing at around 4500-5000 rpm. It's like a sort of rattly-farty-tappy-flappy 'buzz'. It's irritating because now that I've noticed it I end up focussing on it. tbh though, it sounds like it's a perfectly normal trait for these particular beasts. She runs fine, so, meh.

[BusyLittleShop]

Even though an 90º V4 sports perfect primary and second balances they
still vibrate to some degree and the one thing to eliminate if you
feel more vibrations or hear an odd rattle is a loose exhaust system
because it will amplify any of those vibrations to an annoying
level... tap the pipes with the palm of your hand to test if any bolts
points or connections are loose... also check the foot pegs bolts and
anything bolted to the foot pegs...

[adsrox0r]

Update: So I fixed my horrible flappy rattling issue under load....

It was a loose panel. One of the inner 'cheek' fairing panels, the black ones held in with plastic clips, was loose and was tapping away. Re-seated everything in there and put a rubber washer to pack the space behind the clip and voila! After nearly six months of driving me berserk every time I rev through 4k to 5k....gone. All I can hear now is the sweet roar of the V4 again.