1980 gs550e - fuel tap / tank noise

[Agemax]

what carbs have you got, BS or VM, your first post you say vac pipe is on #3 carb and now you say its on #2 carb, so which is it?

[ukjules]

Petcock vacuum goes to carb 2
Bs carbs

(I won't be near bike till later today )

I'll do some tests later and strip the
petcock. ( I'll also re for my one I had to use on long trip
in an emergency as can't remember if that too had the noise issue )

But for years it has done this .
But the diaphragm in the petcock must
open / close almost every second.


Note:
The bike runs like a dream. Tuned spot on.
Does not have a fuel filter (no room or it would)
Totally standard bike.

[tatu]

No, when there is vacuum then the valve opens, when there is no vacuum the valve closes, ie one cycle per engine on and engine off.

Have you tried opening the fuel cap to see if the clanking goes away?

[ukjules]

I will redo tests later this afternoon!

I have taken the fuel cap off a d clanking remains.
Let me check again ...

Re the petcock from z1 enterprises.
It looks to fit as they have emailed. Same dimensions as mine
I'll check prices etc and might try it .

Tests:
-Good sealing vacuum pipe
-Fuel cap off , running along
-Vacuum pipe off but blocked off tank end ?

Any other analysis I can do this eve .
I can also strip it and check internals.

[ukjules]

Bare with - I have some success but using another
fuel tap.

I'll update later with pics but my internals
on the petcock were broke again , the metal bit on the diaphragm

pic is original petcockgs550e standard petcock - no prime.jpg

[ukjules]

Update:

status as was: I am sure this was the original petcock, it might have always done this.
It was clanking along with the pulses from the vacuum tube.
Clanking as the diaphragm for some reason was doing this:

Analysis:
-Riding along with fuel cap off - no change
-engine running on and res position – no change
-it always seemed to be bad when nearing reserve. However when I pushed it into running out on reserve and the clanking pronounced it has been a lot worse.
-Engine running – static – pull vacuum pipe of tank – clanking stops .
the pulses from the vacuum can be felt sucking in (1 a second)
-tried a tighter fit vacuum pipe –no change

Stripped petcock:
As you can see from the picture – the diaphragm metal disk has split in two.
-So we can say that this was the issue. BUT I renewed this from a petcock kit a while ago. (I am afraid I cannot remember the result and if it solved it for a while)
So I must assume it rattles when the diaphragm metal washer is broken only.
And that it broke as was a cheap petcock kit ?

Not good analysis BUT read on:

I have a GSX250e 1980. the fuel tap has res/on and a prime screw.
Fortunately it has 50mm outside to outside bolt holes and m6 bolts.
the internals are also the same diaphragm as the original gs550e petcock.

GSX250e one on and it works fine – no clanking.

Q) If you remove the vacuum pipe you will feel the pulsing ?
(When you put it back on a working fuel tap it sucks in and remains open )
gs550e standard petcock - internals - disc broken - tapping pulse.jpg

[ukjules]

My bike with the gsx250e 1980 petcock.

It works fine (for the last 3 miles)
and has the reserve screw !! so needed when the bike is left for a while !!!

m6 screws
50-50mm outside to outside holes
gsx250e 1980 petcock on a gs550e 1980- fits and works - has prime screw.jpg

[ukjules]

Update:

I am convinced I have heard the tapping again using another
petcock. The gsx250 one I used. It's slight but it's there.
I am flummoxed !

I will not stop until I get to the bottom of this.

: I have ordered a petcock kit and will
put that in my original one ( the one with just
On and Res).
I will then test like that and we must assume it will
be fine.( For a while at least )

: When I do that I'll strip the one in now ( the gsx250
one , that seems to have started tapping
( We would expect here the petcock diaphragm beginning to break )

Notes:
The gsx one is old and the internals were 20 plus
years old and diaphragm might be old , inflexible )

I am assuming the above as it simply cannot
be the vacuum ruining the diaphragms in the petcock ?

I use good quality fuel only !!!

I'll report when I do the above and then
put down full analysis.

But I'd someone has a gs550et 1980 this has to have happened
before ?

[ukjules]

Update:
A 200 mile camping trip and bike was fine.
Using the gsx250e 1980 tap with prime.
It works a treat but I am sure I hear tapping but only when 3/4 full.
Madness.

Whatever it works . Might help others with these petcock locating issues.

When the repair kit arrives I'll inspect .

[egleaves]

Ukjules, I have the same problem and the same petcock as your original.

I started out chasing a tapping noise that I thought was originating from the valve train, but turned out to be the petcock. Before I heard the wisdom of the sages I had already ordered a rebuild kit for my 1980 gs550e. Kit arrived...diaphragm wasn't even close to what I needed. Ordered a whole new OEM petcock from local shop for my 1980 gs550e. Part arrived....not even close to the petcock I just took off my tank. I'm not sure what year my tank is.

Tomorrow when I get to a real keyboard i'm going to start a new thread with more details and some pics. Our mysteries have a lot in common.

[Gorminrider]

I haven't had this but trying to think what this could be! Yes it'll be rythmic to the valves of course if it is the vacuum function creating it ...Stil,l disconnecting AND PLUGGING the vacuum line when on prime should confirm it is the vacuum of engine.

hmm. Any chance the spring against the diaphragm is on the wrong side? (it holds the piston and its oring to close fuel...)

I was also thinking it's possible that the vacuum piston is tapping on the doodad circular bit that holds piston from sealing when turned to prime but not in ukjules case because he has the ol'style prime screw...

[Gorminrider]

I bought a petcock at the scrapyard today...and tore it down to fix it. I figure it dates from 1983 -1985? when we were getting 450 T's in Canada
IT reminded me of this thread....it may have an answer why some make tapping noises: its diaghragm has two layers of thin "rubber" that sheath a thin round disc inside them..this disc pops in and out like the old oilcans (if you know the ones I mean- if not maybe squeezing a beer can will duplicate it)
Anyways, it makes a definite noise as it "pops" when vacuum is applied... to pull the plunger back from the fuel passage..In fact, when vacuum is not happening, the petcock stays open awhile before popping back to the original closed state. This might be its purpose... but I can get it to make quite a racket sucking and blowing on the vacuum line . If there were sufficient backpressure on every pulse of the valves, then I can see this being a cause...

It is a design of diaphragm I've never seen before-never seen one with this internal metal (or is it plastic? ) If one of you have this you'd know it -it's stiff except on it's edge that is under the metal petcock assembly. Everything else is the same as my other petcocks, including the thin metal backing disc on the outside of the diaphragm...