Rebuild 1979 gs 850 petcock

[Jonesz]

I have done a search or two but am still wondering. I am restoring a 79 gs850 (hasn't been ridden since 2000).The petcock initially was stuck open on prime. I did manage to get it freed up but after installation the petcock slowly drips in the run or reserve position. I am thinking that I have to rebuild the petcock and find that there are a couple of seals etc available oem for the petcock. Does anyone know what parts I should order or is there a reputable kit that is better? Would rather have the oem petcock setup than an aftermarket one, but may be convinced to order a replacement (aftermarket if a reliable source can be found) if necessary. What is the current thinking on petcock replacement/ repair?

[cowboyup3371]

Rebuilds don’t work most times so better to get an OEM petcock although Z1 sells a decent one

[Phred]

I tried to rebuild mine and ended up getting a new one. As Cowboy up says rebuilds don't work most of the time. The one I got from Z1 has given me no problems. Had to enlarge one of the mounting bolt holes as it was a 32nd of an inch from fitting properly and i could not get the second bolt to engage the threads. Comes with new gaskets as well.

[rphillips]

May be worth taking apart, these things are really simple. Inspect & clean the seat & seal good & stretch the spring just'a little. Many folks around here don't have much luck with rebuilding them, but I've rebuilt several with ebay kits with no problems. This discussion has been around here for yrs. & it seems most around here recommend a new "Suzuki" OEM ( Not aftermarket ) pet cock, & forget about it for the next 15 yrs.... Decisions, decisions, good luck

[Jonesz]

Thanks to all for the helpful replies. May take it apart, clean and do the spring stretch thing. If that doesn't work then likely a new one will be bought.Nothing to lose right?

[Gorminrider]

...the tiny o-rings on the plunger seal are crucial,IMO... In operation, the plunger wiggles in and out per the vacuum applied from the engine...If the diaphragm seems to be ok , I'd go straight to cleaning the bore out and looking for just the tiny o-ring at the hardware store...I'm not sure "rebuild kits" get this right especially as there's bound to be a teeny bit of wear on the alloy bore too.

[Jonesz]

...the tiny o-rings on the plunger seal are crucial,IMO... In operation, the plunger wiggles in and out per the vacuum applied from the engine...If the diaphragm seems to be ok , I'd go straight to cleaning the bore out and looking for just the tiny o-ring at the hardware store...I'm not sure "rebuild kits" get this right especially as there's bound to be a teeny bit of wear on the alloy bore too.

Will check that as well. Thanx

[Jonesz]

Tried to order an OEM petcock but they are on back order so the dealer ordered me new gaskets and I am going to rebuild the one on my 79 gs850 with only 17,000 kms on it (just over 10,000 miles). Will let you know how it works out when the parts arrive. BTW up here on the Canadian prairies a new oem petcock is $143 Cdn. including tax or approx. 110 US $!!

[Grimly]

I had success rebuilding one of mine, but the main reason it failed was the holed rubber sheet had stuck and torn slightly around the holes, so when I replaced that I buffed the mating surfaces inside, to make sure it would take longer to stick and catch. I rubbed the surfaces with 1000-grade emery cloth and polished them with T-cut. If any of the other parts had failed, I'm not sure the rebuild would have been any good, as seems to be the common complaint with the kits.
Also, I used OEM Suzuki parts - I've got no faith at all in the aftermarket rebuild kits.

[Jonesz]

I had success rebuilding one of mine, but the main reason it failed was the holed rubber sheet had stuck and torn slightly around the holes, so when I replaced that I buffed the mating surfaces inside, to make sure it would take longer to stick and catch. I rubbed the surfaces with 1000-grade emery cloth and polished them with T-cut. If any of the other parts had failed, I'm not sure the rebuild would have been any good, as seems to be the common complaint with the kits.
Also, I used OEM Suzuki parts - I've got no faith at all in the aftermarket rebuild kits.

That appears to be the problem with my petcock. Visually it looks like the rubber with 4 holes has been worn/torn at couple of hole edges. I ordered oem parts and will take your advice on cleaning up the surfaces with 1000 or 2000 grit. Not much to lose in trying other than $20.

[rphillips]

I'd think the rubber diaphragm + vacuum will control the opening of the valve, the spring, "O" ring, & seat will control the closing & sealing of the valve. Hoping for the best in both directions, good luck.

[superawesome]

I successfully rebuilt mine with a "Tourmax" kit from ebay and it's been working for three years now. Picture shows how much the old washer shrunk in 40 years, no wonder it leaked...
WP_20171020_14_56_36_Pro.resized.jpg

[Jonesz]

My new petcock gaskets showed up so today I took it apart again and put in a new "4 hole gasket". and a new round gasket that seals the selector switch. Only thing beyond that was took Grimly's advice and cleaned up the inner plate on the selector with 1000 then 2000 grit paper on a sheet of glass to keep it flat. Buttoned it back up. threw in some gas and NO DRIPS and when primer was selected the gas poured out as it should. Looks like I got the old one fixed for 13 bucks instead of over 140 Cdn. Fingers crossed, the petcock really had only a little over 10,000 actual miles on it and nothing seems loose or worn other than the 4 hole gasket. Thanks all for the advice.

[Jonesz]

BTW does anyone use a smear of brake grease in the petcock to lube the selector & four hole gasket? Just wondering as the new setup is quite a bit stiffer to operate. Could be a good thing I guess but thinking it may wear faster.
Jonesz

[Gorminrider]

I've never had luck greasing petcocks and I've tried several types of grease MAINLY because the gasoline fumes attack them I think...and between any two sliding surfaces the fumes can't go, neither can the grease -it gets squeezed out. I even think Some greases will swell the viton-or-nitrile rubber or the nylon "selector" inside and make it worse but that's just a feeling.

Naturally, applies to carbs too. You can put a drop of oil on shafts and cables but nothing inside.
I've even fiddled with thespring clip (on-off-prime printed) that holds the tap-and-selector. The little tabs that hold the clip, but it's risky.
Some petcocks I have are just really tight and hard to turn, especially with gloves. I mean to give up lubrication and just make the handle longer

But yours may "wear in" and be ok.