Noise from engine/tank area at 5000 rpm and 6500 rpm...

Greetings from London fellow Viffers!

I have just bought a 2006 800 VTEC with 20,000 miles, in great condition. Everything works as it should... I think, my worry is that when accelerating briskly (half to WOT) in low gears I'm getting a strange buzzing noise... briefly at 5k rpm and as VTEC kicks in. This lasts only a second or so, and becomes less and less audible the slower I accelerate... if I'm gentle there's no buzzing sound at all. Sounds a bit like running a wooden ruler along metal railings, quickly, raspy, buzzy.

The flapper valve appears NOT to be working... I have also tried disconnecting it (blocking the hose, taping the pipe) and there's no difference. I've tried disconnecting the PAIR, left the pipes in place but disconnected the electrical block above the rear right cylinder, no difference. Removed the black metal exhaust plate behind the right hand footrest/rear brake hanger, put some silencer packing between it and the pipes to dampen it, no difference. So I'm thinking it must be valve noise, but wouldn't it rattle at all engine speeds? Doesn't do it in neutral if I rev the engine, nor in gear ditto at a standstill, only when we are making progress at a rate of knots. Or is it normal??? I've replaced the air filter and changed the oil. The valves were NOT checked at 16,000 miles, according to the service history.

What do you guys think? Get a valve job done quick? The bike is otherwise smooth and goes like it should.

Thank you for reading this, and I'm grateful for any input!

Sam

 

The flapper uses engine vacuum to open, but that is controlled by an electric solenoid, by the ECU. 5500 rpm is where it should operate. I don't understand why, but the flapper only operates when the bike is in gear so you won't get it to activate in neutral on the centrestand. If you pull off the neutral switch connector on the clutch cover, then the flapper will operate in neutral. Suggest you do this and rev the bike up, at least you can visually see if the flapper operates in conjunction with your noise. The solenoid can be disconnected using it's connector.

If it is not this, then one of the cam chain tensioners may have failed, apparently not too uncommon on a 6th gen, and not expensive or difficult to fix.

 

Thanks Cadbury! I did unhook the neutral switch, and there was no sign of life. It's not the flapper valve itself cos I sucked on the end of it. Mysterious. If it was the cct wouldn't it be noisy at idle, etc?

 

The 3rd gen bikes (90-93) have a resonant vibration between 5k and 6k rpm. Honda put weights on the footpegs to try to damp it out. It buzzes like it's coming out of the fuel tank, but nobody has figured it out.

You are on the right track to try to isolate components and use rubber sheet to fill in gaps, etc. Sorry not much help but feel your pain...

 

Thanks KB. A mechanic whom I trust is going to give it a spin tomorrow and see if he can diagnose. I'm thinking along the lines of the solenoid valve for the non-functioning flapper valve... that could be noisy, and the noise is chiming in when the flapper should operate... I really don't think it's a cct, idle is smooth and quiet.

 

Funny KB, i get that sound on one of my gen3 nikes, the 91. The 93 does'nt make that sound you mentioned. Makes me like carbureted bikes more and more. Hope op sorts oot his problem.

 

Howdy Rider, maybe they got it sorted oot and fixed by 93, which is after all the best year vfr ever...

 

So the mechanic says it's definitely induction noise, not valves. Phew. He also thinks it's likely related in some way to the non-functioning solenoid valve that connects to the flapper. So that's ok then. Thanks for all your input, guys!

 

So it's not another case of missing tank "buffers", the rubber 1" pieces on each side between tank and frame ?

 

No sir, they are present and correct.