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petcock / fuel cock '79 GS400

  • Thread starter Thread starter brettule
  • Start date Start date
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brettule

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I've got the smallest of drips coming from the petcock on my 1979 GS400, it mostly drips when switching from reserve to normal position when I've filled the tank up. A complete new petcock seems to cost around $200-$300 USD so two questions:

1. Is there a reliable rebuild kit for a fraction of the price?
2. If not, is there a reliable petcock to suit at a fraction of the price?
3. Should I suck it up and spend $300 USD on an OEM fuel tap for a bike that cost me $500?
 
Remove petcock from tank and measure the centerline spacing of mounting bolts. A common unit has 44 mm , but some have 46 or 50 mm spacing.
Do you want to keep the vacuum type petcock?
 
I'm away from the bike for a couple of weeks so can't measure right now, but for arguments sake lets say it's the common 44mm unit. If I remove the vacuum type petcock isn't there a danger it will floor the carbies and pollute the oil just like if the petcock was set to Prime constantly?
 
Yep, if you don't have a vacuum petcock and you leave it on there is a high probability of over flowing the carbs.

Rebuild kits of all types have not proven to be reliable. Maybe a 10% to 15% success rate.
 
JTGS850GL said:
Rebuild kits of all types have not proven to be reliable. Maybe a 10% to 15% success rate.
Click to expand...

Wow, that's terrible. I certainly won't head down that path then. So if I want to retain the vacuum what options are left open to me?
 
Doesn't the carb/block just fill up with gas if BOTH the petcock is left open AND the float bowls are stuck or the "fuel inlet needle valves" rather? Does this happen that often? <---please correct me if I'm wrong :)
 
C_OUELLET said:
Doesn't the carb/block just fill up with gas if BOTH the petcock is left open AND the float bowls are stuck or the "fuel inlet needle valves" rather? Does this happen that often? <---please correct me if I'm wrong :)
Click to expand...
Yeah, that's what I would have thought, the floats in the bowl act like the float in your cistern and cut off the flow when there is enough fuel in the bowl. Apparently this isn't enough because I've read several reports here that if you leave the fuel tap on prime you'll pollute the engine oil and need to drain and replace it.
 
The floats are rarely perfect. Over time they will leak a small amount. Doesn't take much of a leak to overflow the float bowls. It's the reason why vacuum operated petcocks were created in the first place.
 
I'd further suggest another reason is so the Japanese could sell motorcycles to people used to driving cars where you never had to turn the fuel on and off.
 
Probably, and now we have automatic braking, self parking, hazard alert cameras, etc. pretty soon , drivers will be optional!
 
brettule said:
Yeah, that's what I would have thought, the floats in the bowl act like the float in your cistern and cut off the flow when there is enough fuel in the bowl. Apparently this isn't enough because I've read several reports here that if you leave the fuel tap on prime you'll pollute the engine oil and need to drain and replace it.
Click to expand...
...a bad vacuum-type tap can cause the oil sump to fill with gas even when on "Run" or "Reserve"...there are TWO ways gasoline can fill the sump:: either the vacuum diaphragm is cracked/holed = leaks and gas goes down the vacuum tube into the engine via carb throat OR if the carb-float needles are weak and again...overflows via carb throat into the sump. I think an interesting factor in the second case is the bike being tilted forward on it's center stand.-gasoline flows forward instead of back into the airbox where there'd be a chance of catching the issue...
Rebuild kits probably fail because they seem to be just the rubber bits...and that is not the only way these taps can fail. However, you can sometimes disassemble them and get some more life out of them and tereafter Just park your bike on a slope to be safer...
 
chef1366 said:
78s were 400s and 79s were 425s
Same part number for the 550 and a lot less
http://www.partsoutlaw.com/oemparts/a/suz/50d3f590f8700230d8b4c6bb/fuel-cock
Click to expand...

I'm finally reunited with my moto and measured the petcock bolt spacing at 44mm. So is the link above still the best value for money if I want a vacuum petcock for mine, the full assembly? Since they are OEM parts can I just buy the gaskets and o-rings or does this still fall under the banner of "petcock repair kit" which has a 10-15% success rate?
 
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