fuelcock/petcock replacement

[dpep]

Vacuum petcock test


I ordered through Amazon Prime (no shipping charge) three vacuum petcocks for my '81 GS850G. Each was from a different vendor and had a different price. I ordered them all from Amazon so shipping cost could be omitted from the comparison. The price you see in the pictures is as listed on the site before taxes (7% in Florida). I could have used ebay or most any motorcycle parts vendor and gotten the exact same item.

First I will familiarize you with the state of the art testing facility utilized in making these comparisons.




Siphon hose, drain hose, 10mm socket & wrench, portable light



For each petcock I siphoned all of the gas in a nearly full five gallon can into the gas tank. I then put a bucket under the petcock. I put it in the ON position for 12 hours after which I put in the RESERVE position for another 12 hours.

After that I connected a hose from the petcock back into the five gallon can and switched to PRIME to flow the gas back into the can. When the tank is almost empty it helps to tilt and shake it to get as much of the gas as possible through the petcock and out of the tank. That will help keep and remaining fuel from leaking out of the top when you turn the tank upside down to swap to the next petcock.



...Continued

[dpep]

Once all of the petcocks arrived and were out of their boxes the first thing that struck me was how identical they were in appearance. Even the boxes and sealed plastic bags they arrived in were identical. This was the same petcock being sold by three different vendors. I was careful to keep each of them in or very near their boxes which I had marked. Otherwise I would not have been able to tell them apart.



The included gasket was just a tad oversized but could be fitted into the grooves. The gaskets for all three were off in exactly the same place by exactly the same amount which adds to the evidence they all came from the same place.



Though I am too lazy to research it I suspect there may be only one Chinese company churning these things out. If there is more than one they all work with the same specs and tooling. The only observable differences were in the resistance to moving the lever. One was initially a little easier to move but after hitting them all with some penetrating oil and working the lever back and forth a few times that difference became minimal.

The most expensive of the three included a hokey pair of vinyl gloves in the box. It was the one that was initially easier to turn but it was also the only one that had a noticeable machine flaw. There was a thin tab of metal partially covering one of the bolt holes. It was easily flicked out with a screw driver, but it dispelled any curiosity as to whether the higher price bought any additional quality control.



Results

They all worked. During the three test sessions not a drop of gasoline hit my catch bucket. If I were to again need to replace a petcock I would definitely take one of these finished assemblies over the rebuild route. They are cheap enough you could buy two and test as I did. The odds that both would be bad have to be tiny. More likely you would just have a spare for possible future use.

And you can buy cheap. The only thing you MAY get by paying more is faster delivery time. The cheapest of these three performed as well as the most expensive. But it was sent USPS and took three or four more days to arrive than the other two which were Amazon delivered.


For me a bonus from this testing exercise was learning about this new (to me) style trick siphon hose. All you do is jiggle it down in the liquid for a few seconds and it starts flowing. No pumps, no drills, no gasoline in the mouth. Now that is progress.



...

[rphillips]

Yep, another reason to love this place, thanks

[93Bandit]

Thank you for the excellent testing, Sir! That looks like the check ball style siphon, those things are great!

I only have one question about the valves: will a vacuum source affect how these valves seal? I wonder if they only sealed because you didn't apply vacuum to them yet?

[Gorminrider]

Thank you for the excellent testing, Sir! That looks like the check ball style siphon, those things are great!

I only have one question about the valves: will a vacuum source affect how these valves seal? I wonder if they only sealed because you didn't apply vacuum to them yet?

Good-thought! it occurs to me a vacuum test comparison could be done with a large syringe and a hose to suit...the amount of vacuum needed for flow is gauged by the pull required...

as to "single-factory", personally, I rely upon it across Amazon, ebay, ali-express..if it looks the same- it is the same (usually the same picture is used) so beyond price and shipping I would recommend perusal of feedback- I pay a little more for the best feedback as a ratio per seller's number of sales...

[rphillips]

Vacuum shouldn't have anything to do with the valve sealing back, vacuum pulls the valve open against the spring pressure & the lack of vacuum only releases the spring so it can reseal the valve. Takes very little vacuum to open valve, put on a piece of hose on the vacuum nipple & gently suck on it with your mouth, you can actually feel the valve open & close. No gas in mouth unless there is a hole in diaphragm. Amazing how little vacuum it takes.

[Gorminrider]

^^^but that is the rub- too weak a spring(too easy to open) means fuel pressure can do the same thing. Fuel pressure in a gravity feed varies while some some petcocks are built for fuel pumps where pressure is consistent. One may work for the other but my experience suggests they may not

[93Bandit]

Vacuum shouldn't have anything to do with the valve sealing back, vacuum pulls the valve open against the spring pressure & the lack of vacuum only releases the spring so it can reseal the valve. Takes very little vacuum to open valve, put on a piece of hose on the vacuum nipple & gently suck on it with your mouth, you can actually feel the valve open & close. No gas in mouth unless there is a hole in diaphragm. Amazing how little vacuum it takes.

I understand the operation. My concern is if it does infact reseal properly after Vacuum has been applied and then removed. Simply put, will these valves start leaking after a dynamic test? The static test performed is very valuable information and has convinced me to try one. I just wonder about the results of a dynamic test?

[sacruickshank]

After my failed attempt at converting the valve from my '81 550T, add me to the list of "just ordered a $20 petcock from AMZN, let's see how it works"

[dpep]

One thing I discovered when mounting on the bike is there a potential routing issue for the fuel line. The fuel nozzle on the oem points to the front into open space. On these the nozzle points to the inside of the bike and on the 850 the opening is less than an inch from the side of the airbox. I first tried routing the line by the most direct route turning it toward the front. Because of the tight space however that created a crimp in the bend.

I ended up routing the line from the carbs over the top of the airbox and down to the petcock nozzle which was still a tight fit but straight enough that there was no crimping.

It is not a deal breaker. Just keep in mind that you may have to do a little work around. I also thought about using some thick walled marine hose that I had in the garage for the line. It is stiff to work with, but it is not going to crimp.
...

[sacruickshank]

One thing I discovered when mounting on the bike is there a potential routing issue for the fuel line. The fuel nozzle on the oem points to the front into open space. On these the nozzle points to the inside of the bike and on the 850 the opening is less than an inch from the side of the airbox. I first tried routing the line by the most direct route turning it toward the front. Because of the tight space however that created a crimp in the bend.

I ended up routing the line from the carbs over the top of the airbox and down to the petcock nozzle which was still a tight fit but straight enough that there was no crimping.

It is not a deal breaker. Just keep in mind that you may have to do a little work around. I also thought about using some thick walled marine hose that I had in the garage for the line. It is stiff to work with, but it is not going to crimp.
...

I bought a pack of 90 degree brass elbows that allow more creative routing without bending the tubes alot. I've had cheap plastic fuel filters break due to the pressure from teh bends

[dpep]

I bought a pack of 90 degree brass elbows that allow more creative routing without bending the tubes a lot.

Good idea. Do you have more detail on the product--picture or link perhaps? Most of what I saw was threaded and/or too thick to serve the purpose; hence the resort to thicker fuel line. But s proper fitting elbow would for sure be the better option.

[Jonesz]

Just received my "Chinese Petcock" ordered through Amazon but believe all sellers are selling the same junk. Before going whole hog and installing the tank on my bike I tried the new petcock. It seemed to hold gas adequately and did not drip when installed in the tank. However, when I applied vacuum with a small hand vacuum pump to check how it operated as it would on the bike, it flowed fuel in Res. & On position. A problem arose when I removed the vacuum and the petcock continued to drip fuel. I now have a new petcock that has the identical problem to the 43 year old one that I was trying to replace. Looks to me like it is a crap shoot when ordering these knock offs. It may well be that you might have to order several before finding one that works properly. I have no intention of using the new one thinking that it will leak fuel and likely drip gas on to my shop floor creating a severe fire hazard. Gorminrider had it right when he asked how the petcocks resealed after vacuum was applied.
Don't know what to do now as I don't want to start ordering Chinese knock offs and waiting several weeks to find out the replacement is just as crappy as the one I received today after waiting over 3 weeks. The one I ordered was supposed to be and was advertised on Amazon as "shipped from Canada" but the seller (Topzan) was fraudulent when posting the ad and it was shipped from China.Really got taken here as I paid extra $ due to the seller stating my order would be shipped from Canada and thus would save waiting time. The ad is here: https://www.amazon.ca/gp/product/B08...?ie=UTF8&psc=1
Anybody have any other thoughts about what to do to repair/ replace my 1979 GS 850 petcock.

[Rich82GS750TZ]

Jonesz, did you look for one here? https://www.georgefixs.com

[Jonesz]

Jonesz, did you look for one here? https://www.georgefixs.com

I had emailed them two inquiries before ordering the chinese one from Amazon. No answer either time. I did see where another poster had recommended Georgefixs but?