Buzz between 4K and 4500 -- much worse!

Greetings!
I have read 4-5 posts about buzzing, rattling, whatever, and mine buzzes between 4K and 4500. I think it is the baffles in both mufflers. With a rag draped over them to keep them from 'ringing', if I rap them with a knuckle they buzz pretty good. So what can I expect to pay for a new pair, and is the 'rap test' sufficient to know if a used set are any good?
Thanx

update -- added post below with new symptoms

 

Re: Buzz between 4K and 4500

Actual Yamaha NEW=nearly impossible to find. Take 'em off and shake them, you'll find out if anything big is broke loose inside. Most likely you'll be 'mail ordering' your replacements in some fashion (eBay or whatever) and won't get to "rap test" them, you will end up depending on the honesty of the person you bought them from. As far as what you can expect to pay---good luck. For my two 550 Seca projects: (1) for the '81 cost me $125, it is perfect. The other was $90, it's fine with a small scratch. Then I found a near-perfect PAIR for the '83 for $135 for both. I got both sets from (different) online motorcycle salvage yards, but the collector and the head pipes for the '81 came off eBay.

 

Re: Buzz between 4K and 4500

lol honda pipes always work nice!

 

Re: Buzz between 4K and 4500

bigfitz52 -- super thanks. Sounds like this is going to be a tough one. Thing is, I know it's just gonna get worse.

 

Re: Buzz between 4K and 4500

Harley pips are another cheap alternative, I really need to upload a few pics of mine. I love the sound and they almost look like they belong there. My bike has a pretty good buzz that I can feel in my seat in that same 4000-4500 RPM range. Above 4500 it goes away entirely and she's VERY smooth. I am guessing that is a factory design issue, but if it is audible (you can hear it) then I'd say you have something loose. I can't hear mine, only feel it.

 

Me again,

It may be that the xj750 is just louder than my other bikes, but the buzz seems to have gotten much worst all the sudden. The biggest thing is it starts and stops like flipping a switch. It only happens when I am going over 40 MPH, and it is related to engine speed, not road speed. If I pull in the clutch I can rev the engine through the buzz zone and make it come and go. I noticed this first changing gears because it happens when clutching and it is truly loud.

Weird, and kinda worrying. Suggestions? Thanks!

 

I have a buzz in mine from 4-5k, but its my gas cap vibrating.

 

The 750R has a collector box, like the 550s. My '81, which has 23K on the bike and a pre-owned collector box with probably a comparable amount of miles, HOWLS at certain RPMs, whereas my 8K miles '83, with its original collector box (and "new" pre-owned mufflers) doesn't have the same howl.
The collector box has a baffle system sandwiched into it; if it's not something in one of the muffler cans I'll betcha you might have some collector box baffle erosion going on. I'm pretty sure I do. (I've got a spare but I'm too lazy to swap it to find out.) Make sure you don't have an exhaust leak at the head or where the pipes meet the box, too.

Check your gas cap too just in case...

 

I have a buzz in my 84 FJ which scared the crap outta me when it started...4-5k it starts letting out like no other. I filed it under the things I never noticed category. I have the Cali model and I through narrowing it down I think it comes from the clamp that goes around the gas vapor canister on the left side of the tank...long story short, stuff is gonna rattle.

 

Thanks again guys --
Seems y'all think its not serious. I'll check out the gas cap and collector box for my peace of mind.
I turned around and rode home the other day, worrying that it was something inside, cam chain or something, but I will put it on my 'ignore list', stop worrying and just enjoy the ride.
-- clh

 

My 82 750 max buzzes between 4500 - 5000 after that it quits. The way it feels it feels like harmonics. I also notice when my bike is in its ZEN mode, (when every thing is in tuned with each other) it is less noticeable.

 

It might be an early sign that you'll be needing Exhaust Donuts soon.

Also, at 4,500 Rpm's ... +/- 500 Rpm's ... Everything is turning at almost 1:1 ... with the Bike's Engine and Wheels turning at the same revs.

At low Manifold Vacuum you can hear everything. Particularly, the Middle Gear which ... depending upon what Oil you use ... will be be a softened gear mesh noise to a Banshee Howl depending on viscosity of that Oil.