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Purpose of oem petcock diaphragm

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What exactly is the purpose of the diaphragm and vacuum line to petcock?

Contemplating deleting while having the tank off and drained and fixed. Previous owner put to long of a bolt in the radiator shroud and shoved a hole right into the tank and just found that out today. People these days I tell ya!

ImageUploadedByThumper Talk1447380196.977005.jpg

But yeah just curious on the pet cock setup , I've always had non vaccum fuel valves on my dirtbikes.

Thanks!

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I would guess to pass emission requirements due to being street legal due to the way it operates.

I ditched the aweful vacuum petcock for a Yamaha raptor manual petcock.

https://www.thumpertalk.com/shop/Yamaha-FUEL-COCK-ASSY-1-5LP-24500-01-00-p1000322768.html

Edited by Kx250FRiDeR651
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not sure the over-all purpose, but it doesnt free-flow without a vacuum signal and this makes the fuel system more reliable over time on a carb setup imo .. the chances of the crankcase getting flooded are reduced and if it sits alot, less fuel is distilled out of the carb which equals less junk buildup ... on a regular petcock you could of course just turn it off .. and on .. if you remember ..

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Ok, thanks for the info guys.

Has anyone or a lot of ppl had problems with the oem vaccum style petcock? Just debating if I should delete.

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The diaphragm is what allows vacuum to open the valve allowing fuel to flow. You will hear a lot of people swap them out for a standard manual petcock. They can fail over time, but they can also work fine. If your carb is good shape (mainly the needle valve and seat o-rings) it doesn't matter much until you need to remove the tank. 

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I would guess to pass emission requirements due to being street legal due to the way it operates.

 

 

 

Ding Ding Ding!!!!!!  :D :D :D

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I think your all wrong!!!

 

The companys are just covering their a$$, if someone started up their bike, rode down the street and it stalled in an intersection cuz the carb ran out of gas and they got clobbered, the companies would  be afraid of being sued.

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Also for safety reasons...If you crash & bike stalls, fuel shuts off.

 

 

This is the reason, and its probably more for environmental reasons than safety. Gotta keep the greenies happy. They don't care if you crash and burn, just don't trample any bushes in the process.

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OEM's have been using vacuum petcocks since the late 70's/early 80's. It may have been a safety item, but I had always thought it was just convenience. 

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I think your all wrong!!!

 

The companys are just covering their a$$, if someone started up their bike, rode down the street and it stalled in an intersection cuz the carb ran out of gas and they got clobbered, the companies would  be afraid of being sued.

Yep, liability...pretty much what it sums up to.

Edited by Throttle5

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OEM's have been using vacuum petcocks since the late 70's/early 80's. It may have been a safety item, but I had always thought it was just convenience. 

 

That's the other thing CONVENIENCE,  people just want to be able to turn the key jump on and go.  It's bad enough for people that can't walk and chew gum at the same time to have to pull the choke, pull in the clutch, kick stand up, turn the key, hit the starter button, without also having to turn on the gas petcock.  Man, at my age it's amazing I can remember to do all that. haha.

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lol thanks all for the replies. Love hearing the feed back.

Since my bike is low mile and ultra clean my carb is in good shape. I'll just keep the oem set up for now and have the spare manual petcock sitting in the garage for when and if this one ever fails.

Oh btw don't pull the tank with it on PRI lol found out what that was for the hard way. Stands for PRIME! So for ppl that don't know when you pull your tank you can leave on ON, and gas will not come out because it needs vaccum to come on!

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I think your all wrong!!!

 

The companys are just covering their a$$, if someone started up their bike, rode down the street and it stalled in an intersection cuz the carb ran out of gas and they got clobbered, the companies would  be afraid of being sued.

 

 

It's been an EPA mandate going on ten years.

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It's been an EPA mandate going on ten years.

Who would know that $hit, you must work for the EPA, lol

 

But, as Bandit pointed out they have been using them since the 70's. And I believe at the top of their list for using them, back then, was liability and customer convenience. :ride:

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Who would know that $hit, you must work for the EPA, lol

 

 

People who have been lifelong bikers and pay attention, LOL.

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This is the reason, and its probably more for environmental reasons than safety. Gotta keep the greenies happy. They don't care if you crash and burn, just don't trample any bushes in the process.

Or this, LOL !!

1447948074063.jpg

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