Hi all, I am at a loss in my search for a mysterious and annoying buzz somewhere in the engine area (I think). This sounds like a very vague description I know, but I can tell you all, I have searched far and wide, long and hard to find this damn thing.
It comes in around 3900rpm and is gone at around 4400 rpm. It is not the famous fuel line check valve ball rattle as my 1988 K100rt does not have this item (that I can locate). I originally removed various fairing components in an elimination process, all to no avail.
I am suspicious that it may be some sort of resonance developing inside the inlet plenum housing. Is this possible ? Maybe something contacting the plastic side wall ? Or, is it known that anything can cause this noise within the air flow meter ? I would think not, but maybe a long shot.
So any advice or suggestions will be most appreciated, thanks,

Dennis

I just went through that with my 1985 K100 and one thing that was mentioned is the muffler heat shield. I had a buzz coming from mine but did the fix and it's fine now. The factory screw holding the heat shield to the muffler are sometimes a bit too long and when they are tightened up they dead end into their threaded socket but are not completely tight on the heat shield . I put an extra washer behind each screw and the buzz went away.
It's worth a try, Doug

Thanks for your input, but unfortunately this problem is already known to me and I removed the heat shield and polished) the exhaust some time ago. To protect the L.H. pannier I glued some aluminium coated kevlar to the underside, it works well, only needing to reflect the heat when the bike is at standstill.
The buzz continues !!

I had a high pitched Buzz and traced it down eventually to a wrongly routed fuel pipe. Feed /return were routed together and close to the rad hose. As it heated it closed the fuel pipes and a high pitched buzz was there.
Check that the run of the fuel pipes are separate from each other.
It drove me up the wall until I found it.
Ajays

Reading Ajays reply makes me think that it could also come from the fuel pressure regulator mounted on the back of the throttle body.

Yes, I've been wondering about this as well. I presume the regulator consists of a spring and a diaphragm. So iy may be that at certain fuel pressures the spring gets some type of rattle happening in response to the pressure on the opposite side of the diaphragm. Very difficult to access of course, but the sound does sound as though it is coming from well down around the engine rather than up high in the fairing.
I may need an assistant to hold the engine revs steady with the bike stationary while I search.

It should be easy to keep the engine revving steady.
The K100 has a locking screw on the throttle handle. Some model may not have the screw but the threaded hole is there.

Bert, not all handles have the threaded hole fitted. I don't know it it was something particular to government models or not. Of the three I have only one has the hole. Put a rubber band between the grip and the housing if you don't have the hole/bolt?
I would propose otherwise eliminating the regulator by removing the hose from the throttle valve and plugging it with a rubber plug like the other three and run it through the revs. You still have the odd chance that there is a part in there that vibrates, but it is an easy test. If you hear the vibration you can listen to the vacuum hose.

Dennis,

I think I have a similar buzz emanating from my machine, 1991 K100LT. I thought it may have come from the timing chain. I removed the 3 covers and had a bo-peep, but all looked pristine. Mine is a metallic type buzz, between 3000 and 4000 rpm. At this stage I'm trying to ignore it and hope it goes away. I'm eager to learn if you come up with something.

The spring on the none return valve i have seen mentioned a couple of times, is this where the petrol return pipe connects to the tank?

Do i have to undo the nut thats there and will i then see the spring etc as mentioned?

thanks
I also have an annoying buzzing and wanted to check this first.

badgerdid wrote:The spring on the none return valve i have seen mentioned a couple of times, is this where the petrol return pipe connects to the tank?

Do i have to undo the nut thats there and will i then see the spring etc as mentioned?

thanks
I also have an annoying buzzing and wanted to check this first.

That is what it was for me but I was lucky enough to get a replacement brand new and very cheap.
And yes it is as simple as undoing the nut and either replace or repair.

Otherwise the options are a fuel tap which I gave up on or a GOOD set of quick disconnects which would be the best although more expensive option.

Does my 1991 K100 have one of these non-return valve doo-dads?

Thanks everone for the info so far. My bike has the threaded hole for the throttle stop, which I have installed, so that can be used to hold the engine revs steady. I will begin searching in earnest for this buzz very shortly as it is really annoying.
Just to clarrify though, is the elusive fuel line check valve external to the tank, because if it is then I'm almost certain that my bike doesn't have one (being a 1988 model).

Dennis,

The return check valve is inside the tank.
I think the gas tank was modified in 1986 and the newer models don't have it. On the newer models, the return pipe is internally going on the top of the tank.

Thanks Bert, that's what I thought. I am going to investigate the fuel pressure regulator. I also have another regulator on the original engine from the bike, but it looks quite difficult to access with the engine installed. Nothing like a challenge though !

Regards, Dennis

Bert ,
You are correct as usual ..but...the return check valve is outside of the tank on the early models and can be removed.
It was to retain the fuel when removing the tank. Later ones have a higher tube as you say.
It was noisy so the dodge was to remove the spring or remove it altogether.
Ajays.

Ajays wrote:Bert ,
the return check valve is outside of the tank on the early models and can be removed. Ajays.

Just to avoid any confusion: Don't look for this valve outside the tank.
You have to unscrew the return line connection on the tank, and pull the valve out. The check valve is part of the connector.
To remove the ball and the spring, just use a screw driver to pop up the washer on the top of the valve (This is the stopper for the spring).
I first tried just removing the spring but it did stop the problem. I removed the ball too and the noise was gone.

I also have odd noises that I am trying to track down.
I took off the fuel return check valve and looked inside it.
There was NO SPRING, just the ball.
Now does that mean the previous owner removed the spring?
Do I finish the "job" by removing the loose ball?
Of course, with-out that ball, I would have to siphon drain the tank before I could remove it, is that the only downside to the ball removal?

Thanks in advance,
Rick

Yes the ball is normally spring loaded.
On my bike, I first removed the spring, but the ball was still bouncing and the noise was still there. I finally removed the ball too and installed a manual shut off valve. The fuel pressure should be minimal or inexistent on the return line.

I fitted an inline gas valve from a snow blower. They are heat resistant as on most blowers, the gas tank is located over and very close to the engine.
I did this mod 5 years ago.

Bert,
Thanks for the detailed info on the fuel check valve, but I must admit I haven't studied the fuel circuit in enough detail. I have checked closely both tank fittings and they are both welded in, there is no screwed fittings and both hoses are clamped on. This is a 1988 RT so I'm assuming there is no check valve ? Or is is in fact inside the tank and must be accessed by removing the fuel pump etc ?

The check valve was removed in 1986. You don't have one on your bike.

Just removed mine, and the spring was still in so hadnt been done before.
Recently when i started the bike i could smell petrol too, when i removed the check valve it was all rusty? and the ball was stuck in the hole, i had to hit it out with a screwdriver to get it free.

Im hopeing this is why i could smell petrol as it had no where to go, i think some must have been returning as i could hear the buzzz but have not taken it for a run yet as im tarting a few bits up.

Hopefully it might do a bit better mpg now.

Thanks for all the addvice on here my bike is starting to be more enjoyment every day

Good for you!!

Sometimes you smell a bit of petrol as the tank vents underneath and with the warmer weather and the fuel circulating close to the radiator it can heat up considerable.

For interest, yhou have removed the check-valve now. At which rpm's did you get the buzz from the checkvalve. It is completely gone now I assume? Appreciate your info.

Bikes still waiting to be put back together so will let you know when
I have taken it out for a spin. Can't remember what rpm it would start
at, when I would be cruising along I could hear this annoying vibration/rattling
noise over the hummm of the exhaust. Hopefully now sorted.

Took it for a spin today and the noise has gone, yahooooo.

Also the bikes running a lot better, i think because of the fuel not returning it might have been over fuelling before, now she runs sweet.

I'm going to try the same fix, no ball at all.
I'm waiting on parts though for my water/oil pump at the moment.
I should have it all buttoned up by Friday.

Glad you got your bike running sweet, and mystery buzzzz is history.

Rick

Dennis wrote:Hi all, I am at a loss in my search for a mysterious and annoying buzz somewhere in the engine area (I think). This sounds like a very vague description I know, but I can tell you all, I have searched far and wide, long and hard to find this damn thing.
It comes in around 3900rpm and is gone at around 4400 rpm. It is not the famous fuel line check valve ball rattle as my 1988 K100rt does not have this item (that I can locate). I originally removed various fairing components in an elimination process, all to no avail.
I am suspicious that it may be some sort of resonance developing inside the inlet plenum housing. Is this possible ? Maybe something contacting the plastic side wall ? Or, is it known that anything can cause this noise within the air flow meter ? I would think not, but maybe a long shot.
So any advice or suggestions will be most appreciated, thanks,

Dennis

Hello Denis, today i wrote a post about buzzing. You can find it in Frame, wheels part of forum. Ma nick is Nino. Check, maybe you have same problem as me.

Regards

Hi, I chased down a couple of buzzing issues on my 87 k100rt, first was the heat shield acorn nut, next was the ball valve in the tank, and the last was the spring that works the glove box cover holder on the throttle side, drove me nuts, it was really hard to tell were it was coming from.I put a small piece of foam under it and all is well.

Brian

Dennis wrote:Hi all, I am at a loss in my search for a mysterious and annoying buzz somewhere in the engine area (I think). This sounds like a very vague description I know, but I can tell you all, I have searched far and wide, long and hard to find this damn thing.
It comes in around 3900rpm and is gone at around 4400 rpm. It is not the famous fuel line check valve ball rattle as my 1988 K100rt does not have this item (that I can locate). I originally removed various fairing components in an elimination process, all to no avail.
I am suspicious that it may be some sort of resonance developing inside the inlet plenum housing. Is this possible ? Maybe something contacting the plastic side wall ? Or, is it known that anything can cause this noise within the air flow meter ? I would think not, but maybe a long shot.
So any advice or suggestions will be most appreciated, thanks,

Dennis

Hello Denis, when engine is hot just listen on 2000 rpm and more. I am shure you will hear the buzz under the instrument cluster. If it is so "buzzer" is tube of front brakes which goes through frame head. Tube in tube - metal to metal and buzzing is here. My advice is to isolate the brake tube with plastic tape, then put it all together and check the result.
regards