petcocks

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fabiostar
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petcocks

Post by fabiostar »

now just so i know iv got this right. i fitted a new diaphram to the tank, about two weeks ago during this maddness. all was well.

then only the last few days when iv taken the tank off it pisses fuel. so to me this means the diaphram isnt working? or ripped etc? yet i have no fuel coming out the little drain at the bottom of the petcock?

i have fuel flowing with and without vac applied to the vac take off?

i always thought if you had membrane problems it would leak outa the bottom nipple?
the older i get,the faster i was :lol:
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8541Hawk
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Re: petcocks

Post by 8541Hawk »

Oh, Oh I have an answer......though you just want me to share tit with the other members....(inside joke)
and it also might cause other odd, hard to track down, running issues :thumbup:
Loud pipes don't save lives, knowing how to ride your bike will save your life.
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E.Marquez
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Re: petcocks

Post by E.Marquez »

fabiostar wrote: Mon Apr 22, 2019 6:19 pm now just so i know iv got this right. i fitted a new diaphram to the tank, about two weeks ago during this maddness. all was well.

then only the last few days when iv taken the tank off it pisses fuel. so to me this means the diaphram isnt working? or ripped etc? yet i have no fuel coming out the little drain at the bottom of the petcock?

i have fuel flowing with and without vac applied to the vac take off?

i always thought if you had membrane problems it would leak outa the bottom nipple?
If the diaphragm has got a hole yes you will have leakage out the atmospheric vent.

BUT, if the "new" diagram is not sealing to the valve body (like when ebay craptastic are used sometimes)you can have what you do and no leak.
Or the valve pin / o ring on the diaphragm that moves to open/close fuel flow can be misshapen (craptastic non OEM parts). the O ring not the right size ect.

I use craptastic rebuild kits every month on my 90 bike training fleet, I am buying AllBalls these days, but K&L before that.
90% of the time they work no issue, every once and awhile I'll have a petcock or carb kit installed and something not work right....leak, something not seal, seat, ect.. Most times you notice that on install, toss the kit, open another, install, NO ISSUES AT ALL..IOW not a problem with the hard part. My parts guy does not blink an I...doesn't even ask me for used new kit parts back..just credits my account and makes the claim with his supplier later. That tells me its common enough his supplier accepts it as routine claim .

I will say I've done that less with the AllBalls kits then I did with K&L or other craptistic brands.
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8541Hawk
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Re: petcocks

Post by 8541Hawk »

Good description of possible issues but not the cause of the petcock sticking open. :wink:
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E.Marquez
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Re: petcocks

Post by E.Marquez »

8541Hawk wrote: Mon Apr 22, 2019 8:38 pm Good description of possible issues but not the cause of the petcock sticking open. :wink:
Tell that to the petcocks I've found stuck open due to the issues I described above based on actual experience >>LOL


That's not saying its cause, I never did say or imply that, just possibilities to investigate..
Bu hey you have it nailed already so, really knowledge is power, power is good, another diag tip is welcome no matter where its picked up from so do tell.

Without seeing the bike, failing part, kit installed, observing the issues first hand, how did you confirm the issue and what is it?
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fabiostar
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Re: petcocks

Post by fabiostar »

il take it apart and check it over and also

il check my TIT just to be sure :D .. just thought it was strange why it flowed but didnt have any leaks..
the older i get,the faster i was :lol:
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8541Hawk
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Re: petcocks

Post by 8541Hawk »

E.Marquez wrote: Mon Apr 22, 2019 9:09 pm
Tell that to the petcocks I've found stuck open due to the issues I described above based on actual experience >>LOL
Well I will say this can be taken as rather condescending, especially coming from someone who seems to go on about respecting others opinions.
Also what I post is also based on personal experience, even though your last bit might make it seem different....and the LOL, doesn't really help after the BS from the other place.

With that out of the way here is why the petcock can stick open with a good diaphragm and also just appear and possibly go away.
It also might be the root cause of Robs issues.....

What happens is that in the cover plate with the vacuum nipple, there is a small rubber bit inside the nipple, from now on called the "tit" just because.
What this does is just sit in the housing when at atm.
When vacuum is created, the tit moves into the nipple and blocks it off. I can explain the how and why if needed.
When the engine is stopped, atm pressure pushes the tit out of the way, ready from the next run cycle.

Now it might sound odd for this to be in the cover plate but it is there for safety. If the line was always open and you did have a petcock diaphragm failure then fuel would flow down the vacuum line into the cylinder.
If it happened to get lit off, it would run right up the now fuel filled vacuum line and into the tank......Boom..... :eek2 :redface

So if suddenly you petcock stops turning off and you haven't just installed pattern parts, the issue will be that the tit is stuck in the nipple.

What I now think could be the issue with the blue monster is that the tit became partially stuck. this lead to it being very hard to figure out.
When bench tested it could look like all was well because of 2 reasons.
First is that you normally supply a stronger vacuum signal when testing than when the bike is firing up.
Second, can you really tell the visual flow difference between a fully open and say a 3\4 or 1\2 open petcock?

In Robs case, I believe the tit was hung up and still partially blocking the vacuum nipple. This would cause it to block the nipple before the petcock was able to "see" a full vacuum signal.
Which would mean the petcock was only partially open.

It can also explain why the issues just went away, the tit unstuck itself.
The only reason I came to this conclusion was when it was mentioned that the previously functional petcock suddenly stopped shutting off......and I won't even tell you how long it took to find when it happened to me.

Like I told Rob, sorry but kind of glad it happened so I'm not the only one to have this odd ball failure happen to them or yes I do have a touch of personal experience with these bikes :angel: :thumbup:
Loud pipes don't save lives, knowing how to ride your bike will save your life.
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VTRDark
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Re: petcocks

Post by VTRDark »

l check my TIT just to be sure
You have tits now 8O gawd man how much had you been drinking when Bluey went on strike or is this some kind of voodoo :lol:
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fabiostar
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Re: petcocks

Post by fabiostar »

aahh i see said the blind man, i think. im gona pull this apart again and see if reading this while looking at my tit makes sense to me..i cant explain why i had bother with other tanks fitted but this does make sense in how my engine feels , still just doesnt feel like im getting the amount of juice i need, i think iv masked the problem atm by running the pilots very rich but ,i think the tit needs explored a bit more.
the older i get,the faster i was :lol:
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Pete.L
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Re: petcocks

Post by Pete.L »

Any leaky nipple can cause embarrassment


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