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Main Area => General GS500 Discussion => Topic started by: on February 13, 2019, 11:32:57 AM

Title: Petcock diaphragm replacement
Post by: on February 13, 2019, 11:32:57 AM
Hi, I have a GS500E since 1999 with a wonderful performance.
My question is about the fuel petcock. The original one lasted for 15 years. The second one just for 5, I guess it was an old one, not well storaged for a while.
The problem is the diaphragm.  Seems to be theres is no replacement as spare part so you must buy a hole new petcock (part# 44300-01D21). Besides is easy to buy one, it is not easy to import one in my country: taxes, time, paperwork, etc. if you are lucky and you finally get it. Sometimes it gets lost...

I am wondering if anyone found a diaphragm replacement since I will have 2 petcocks with a broken diaphragm and I will have a chance to have spare ones.
Or, may be another petcock of a new model that fits (that you can buy repair kits). Those that has a diaphragm with a cilinder and an O-ring seems to be better.
Sorry for my English, is not my native languaje.
Title: Re: Petcock diaphragm replacement
Post by: Armandorf on February 13, 2019, 01:52:07 PM
In Argentina we have a national manufactured diaphragm, had not tested it yet. But i will soon. if not i am stuck without reserve switch.Almost ran out of fuel several times.

You can change the petcock. look for the replacement here. I thing it was a crf250 or something like that.
Title: Re: Petcock diaphragm replacement
Post by: ShowBizWolf on February 13, 2019, 06:55:58 PM
I had a bit of down time at work so I did some searching. I remember reading something about a Honda petcock swap at least a few times over the years.

Here's a helpful thread I found about it:

Willie, forgive me if the answer is obvious but if it is, I'm missing it. Which petcock are you referring to, the frame mounted one or the tank mounted one?
Title: Re: Petcock diaphragm replacement
Post by: Armandorf on February 14, 2019, 06:37:10 AM
Frame mounted one, the other i beleive it only has an oring.
The diaphragm vacuum operated by the carbs.(oN position)
89-00 model

Quote from: BK
On your GS, when the arrow is facing down your in the "ON" position.
Yep, this is true for all models.  For anyone who cares, the RES and PRI positions are different from the pre-2001 bikes to the 2001+ models.

Code: [Select]

RES  |


Code: [Select]

     |  PRI

Quote from: BK
Just for clarity, you don't need to use the prime position unless you completely run out of fuel.  All priming does is gravity fills your carbs with fuel as opposed the normal suction filling.
Correct on the gravity-feed nature of the PRI position.  But some folks also use the PRI setting (momentarily) when their bike starts sputtering as it runs out of gas, just before switching to the RES setting.  This is because the PRI setting can be more "quick-acting" than the vacuum-dependent RES setting.

Quote from: BK
If I'm not mistaken if you leave it in prime when you shut the bike off all the gas will continue to run out of the overflow on the carbs and there goes a full tank of gas and your MPG.
It would be more correct to say that "the possibility exists" for an overflow.  As long as the fuel system is clean, this should NOT happen.  But if dirt particles or old, gummy fuel causes one of the float needle valves to stay open, then what BK describes is the result.
Title: Re: Petcock diaphragm replacement
Post by: on February 14, 2019, 11:10:48 AM
hi! what a quick response from all! thanks
well, answering in order:
Im in Argentina and I already tested both types of diaphragms offered without success.
Theres a square one, like the original one. And there is a round type. Both have the same problem or bad design, the manufacurer did not respect dimensions correctly or strictly.
First the external ring is a little bit smaller (decimal of mm) so it doesnt fit well on the notch and second, the prominent part that touches the cylinder where the fuel gets in is not enough prominent to do the work. It is almost flat there, so there is a continous leaking.
Ill try to upload a picture so you can see what I refer to.
Regarding the Honda post, I cant download the pictures, Ill do some search on the web- thanks

Now I see that there is a second type of petcock (2005 models?), so responding to ShowBizWolf I have the first model shown on pictures. Im wondering if the other one can be fixed to my bike and if it has spare parts to be repaired.
a question for the next post, What year was the GS introduced in the US?:
Title: Re: Petcock diaphragm replacement
Post by: Armandorf on February 15, 2019, 06:41:12 AM
Once i had a catastrophic failure, draining my tank and putting fuel in oil.

The diaphragm is broken, (i assume, havent opened petcock yet) So even in PRI all the gas was being sucked by the carburetor in the vaccum line directly into the right cylinder.  Plugged the outlet and i use ON as a closed Position, but lost reserve.

I have a Check valve so thats the only way i would use the vaccum line, having a barrier to stop gas from flooding the cylinder.

I would like to make the vaccum petcock functional because almost ever i left the bike in pri and that could be potentially disastrous
Title: Re: Petcock diaphragm replacement
Post by: on February 15, 2019, 07:26:06 AM
I think the best solution is to buy a new petcock, Armandorf. And be sure it is one pretty new unit because the diaphragm gets older either without using it.
Title: Re: Petcock diaphragm replacement
Post by: Armandorf on February 15, 2019, 08:30:17 AM
Looking the price of the petcock best bet is to put an electrovalve that opens fuel flow as you put the ignition in ON, Maybe seems too sophisticated, but really simple in essence. 
Title: Re: Petcock diaphragm replacement
Post by: on February 15, 2019, 12:30:35 PM
thats true, but it is not so easy to find a small one, that can manage fuel, 12 Vcc voltage.. I already did that search.
I think the BMW GS800 uses that but seems to drain considerable current since it uses a relay. and coming form BMW surely is not cheap...