1978 Special Vacuum Petcock Rebuild Question


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S. Central PA
Well I scored myself an XS650, a 1978 Special, and I've started the process of getting it road worthy. After tackling a rebuild of the fuse box I decided to rebuild the petcocks since one was leaking pretty badly. I've read many threads here on the pros and cons of rebuilding vs. replacing with non-vacuum and decided to rebuild. I also read the excellent rebuild thread here: https://www.xs650.com/threads/rebuilding-yamaha-vacuum-operated-fuel-valves-petcocks.20662/

I also read that it is possible that the 1978 SE, being the very first Special, had a one off petcock that was not used on any other model including the 1978 Standard.

I searched eBay in vain for a rebuild kit for the 78 Special, all say they will not fit. The ones listed for the 1978 XS650E look like what I need, but they all say they will not fit. I even went to K&L Supplies website and looked at their Fuel Petcock Repair Kit Application Chart here: https://dealer.klsupply.com//images/fuel-petcock-repair-kits_App.pdf

They don't list one for the 1978 XS650SE! Now I know there must be others out there, with this bike, that have rebuilt their petcocks, any advice?


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Yes, the 1978 petcocks were a one year only style, but I'm pretty sure they were the same on both the Special and the Standard. The ones on my '78 Standard look just like yours .....



..... so I think the rebuild parts sold for them, which are still available, would fit. But, if the leak is because the rubber disc is worn and torn up from the back of the lever rotating against it, often you can just flip the rubber disc over. This presents a fresh, unworn side facing out for the lever to seal against. Also, check the holes on the back of the lever that the fuel flows through. Often they have sharp edges and that's what tears the rubber disc up. If you find that, "break" the sharp edges with a small, sharp pocket knife.

As I mentioned, although the rubber disc is available from Yamaha, it's rather expensive. You can find them cheaper on eBay .....

They do look the same. The gasket set for the XS650E also looked just like the gaskets that came out of my petcocks. I think I'll give it a go with the one listed for the Standard and see what happens.

All the later petcocks had a bigger arm and most likely a bigger rubber disc behind it .....