Cheap petcock for GS850s

[Gorminrider]

Well, I filled the tank halfway and Sad news- mine can't hold back the pressure either. My floats and needles generally do ok -they won't overflow with a full tank turned to Prime- but I still want the vacuum tap to function properly!

I'd tested the tap before installation, by sucking and blowing the relevant orifices and it sealed fine before fitting

yes, I did that too as a preliminary- it can definitely be made to seal -but I'm sadly aware how iffy it is trying to duplicate the fuel pressure by blowing and sucking...

so I took it apart and the spring is definitely lighter gauge than my other one. The diameter is smaller too so I can't swap springs. Too bad.
@Grimly, if you end up with two weak petcocks, perhaps you can put both springs in together? I may try winding a spring from...a guitar string?

...Someday I mean to try calculating the varying mass of the fuel column versus the spring and vacuum ....someday

[Grimly]

Yes, it will be interesting to see what's causing the leak on mine. It might simply be a bit of grit either from the tank or inadequate cleaning during manufacture, or as you say, a weak spring.
I'd tested the tap before installation, by sucking and blowing the relevant orifices and it sealed fine before fitting, which makes me suspect a foreign object in the seat, but maybe the rubber has swelled (or shrunk) in contact with the fuel. It wouldn't be the first time a cheap item used the wrong materials.

[Gorminrider]

Tinker's note (to self, really)
... as you know, whatever spring return is important versus the fuel pressure varying between empty tank and full...my thought is, that many, or at least some, bikes combine vacuum taps with fuel pumps (some also vacuum operated ?) for this very reason (empty vs full) . This might indicate some of the difficulties of buying non-oem fuel taps ... perhaps adjusting to a different spring might help but the pressure variation can be large so the bike might operate differently when the tank is empty...

It may also express the difficulties of rebuild kits beyond flaky o-ring seals ...diaphragm thickness for instance.

[Gorminrider]

Thanks Grimly. I'm filling the tank right up today and will keep an eye on mine disconnected overnite to see if this is model is any better.

[Rich82GS750TZ]

That suck Grim, but thanks for taking one for the team. Please keep updating as you discover anything new.

[Grimly]

Bad news about the cheap petcock.
I had reason to remove the tank and discovered the vacuum valve wasn't sealing off the fuel properly, fuel was dribbling out at quite a rate.
Luckily for me I'd left the master stopcock in place in the fuel line to the carb and that was shut off by habit, so I'd avoided the crankcase-full-of-gas problem.
Anyway, I refitted the old repaired petcock and I'm going to strip the new one to see what the problem is. While at at it, I'll modify it for better fitment.
Oh yes, the vacuum brass pipe insert pulled out of the petcock body when I removed the vacuum tube.
So much for the appearance of quality.
The idea's right, but the fulfilment of it sucks.

[Grimly]

Excellent. I'll be ordering one soon, now that you've provided superb guinea pig service.
I'm fairly sure it will be the same as the one I got in terms of quality, only thing that remains to be seen is the longevity.
Right now I'm immersed in AliEx trying to find something that used to be common as muck - radio switchgear extension shafting.
It would seem nobody uses it any more, so I'll have to make do with some engineering plastic rod and file it to suit. Oddly, the latest craze in building 3D printers has stimulated production of small couplers and rodding, so that's all good.

[Gorminrider]

ONE thing to note: The fuel outlets are 7mm versus the 8mm of the fuel line that suits the carbs inlet pipe... However, it was easy to jam some of the pink hose(per stub on the spare outlet) inside as a sleeve and then the fit is then very tight. A hoseclamp might be fitted to stop any splitting later....
No drips I guess a Highway test is required (preferably uphill) but initially in the shed vacuum function is ok over a long enough period of time. the spare pipe..can be tucked away but eventually I s'pose I'll cut it off and plug it if it isnt useful.
gs400E new petcock-trial-20190319.jpg

[Gorminrider]

400Ex-wrongPetcock.jpg

In the commonly * available petcocks, (as presently I have by necessity above) the fuel hose (blue) must come around the back of the frame and even then, the sidecover needs trimming....the tank cannot be lifted until the hose is removed. Also, the fuel line must be routed in a peculiar way inviting air locks..
I think Grimly's ebay cheapo above might also suit the space available .
* I've "seen" quite a few petcocks that purport to fit the L,T and E incuding correct part numbers.... Quite often, if there's a picture included, it's obvious they will only fit the T and L which have the tap located further forward on a teardrop tank.

[Gorminrider]

Arrived! looks pretty good to me. Holes are an exact fit. Vacuum feature functions .
....I'm experimenting with plugs on the unused outlet(there's two outlets-not a great picture-refer to ebay link above))-what's shown is a tirevalve cap..I'll put a dab of seal-all under it until I'm settled on how well the petcock works in action. The extra outlet might come in handy as an option so I'm loath to plug it permanently yet. I guess I'll try an install very soon...
newEbayPetcock-20190318.jpg

in case anyone's wondering, the tank position on the 450E may be even more restricted than Grimly's 850 above..
(next post)

[Gorminrider]

^^yes, I bought one. Looks to suit ANY of my three suzukis... It'll take forever to get here -usually 5-8 weeks China-Canada per ebay ...but I'll report back when it does arrive.

[Grimly]

Here's one from ebay.ca with two outlets, so you get to choose! hole measurements look right and it goes some way t'wards yer question per drilling out another outlet.
New Fuel Gas Valve Petcock Petrol Tap For Suzuki Katana 600 750 GSX600 GSX750 F | eBay

Excellent spotting!
I've put that on my to-purchase list for next week.

[850 Combat]

Thanks. I stuck a 1982 on GS850/1100G petcock on on a 1980 1000G. It was less expensive compared to the correct one. The extra hose routing is a minor PITA.

[Gorminrider]

Here's one from ebay.ca with two outlets, so you get to choose! hole measurements look right and it goes some way t'wards yer question per drilling out another outlet.
New Fuel Gas Valve Petcock Petrol Tap For Suzuki Katana 600 750 GSX600 GSX750 F | eBay

[Grimly]

Now that is an awesome alternative. I’ve been debating between fuel injection swap or something similar to this with maybe some large blowby carbs, either way I could add a small turbocharger if I wanted to.

If you want to turbo (or supercharge) an SU, google information on the Metro Turbo carb. I had a look with the expectation of using an Eaton M45 blower and an RX7 engine in combination with a blown SU. The Metro Turbo installation would have been a good starting point for setting the carb up the right way - surprisingly, there's not a lot to it.