New petcocks leaking on 1979 XS650

[1979Special]

Hi all. New member here, so hello. I've been enjoying some of the restore threads.

I'm the new owner of a 1979 XS650 Special.
The bike has new gravity petcocks installed when my local shop was syncing the carbs. Both petcocks are leaking. (One more than the other.)
I believe they're leaking when ON/RES, but not when OFF.

I searched here and google, and came across this thread, but the petcocks look like a different design (though that may not matter.). It looks like they're leaking from the back, versus from the front.
In any case, I thought I would check in, and see if anyone had advice to offer. (Thanks in advance!)

Here's a short video of the leak.

And, here's the requisite picture of the bike.

 

[Jan_P]

I would check that all screws is tightened if so I would open and check rubber parts perhaps use sealing chemical

 

[Melnic]

That looks just like the manual petcocks I have on my bike right now.
https://www.amazon.com/gp/product/B07SWJ4N9J

They are one part and a port on left and right. You have to switch the plug/port when you get them on one side.
There
Likely they were not tight enough.
There is also a filter screen on the inside.
You can see how both the outlet and the plug should have a red washer.
you need to find out where its leaking from, the nipple to the hose, the nipple to the petcock, the plug to the petcock (right side on your pic)
The valve knob end or the back to the main case where there is a gasket held onto by 3 screws.

Mine has functioned flawlessly since getting them. I have only put a little more than 100 miles but I have had to pull tank and start bike many times since swapping out the originals. I have rebuilt the original vaccum ones but have not put them on yet.


Nice looking bike BTW!
Good luck.

 

[1979Special]

Hey, Melnik.

I suspect it'll be the back to the main case where there is a gasket held onto by 3 screws. I'll try tightening the one that leaks more, and if it reduces the drip frequency, then I will assume the gasket isn't up to the task.

Have you had to pull your tank and start the bike with the new petcocks? If so, what's the story?

Thanks for the post and good info!

 

[Melnic]

I have a long thread on this bike.
the original vacuum petcocks had diaphragms that were leaky and even leaked when turned on. So pulled them out and put these on.
These new Amazon petcocks seem to work fine for me.

 

[1979Special]

Gotcha. (Yeah, my vacuum petcocks leaked from every conceivable spot.)
Ah, I see. I was just looking at your thread today. Nice work!

 

[Niels B]

You could rebuild the vacuum petcocks if you still got them - they work well after rebuild, I’ve rebuild several.

 

[Melnic]

You could rebuild the vacuum petcocks if you still got them - they work well after rebuild, I’ve rebuild several.

Even if he does not, hopefully he got them back cause the are still worth $.

 

[MaxPete]

When mounting an XS650 petcock, you really do need to use those special fibre washers that fit quite tightly onto the two JIS mounting screws - and they must fit tight on the screw threads. I have found that an old used washer generally will leak and so I buy them buy the dozen - just in case.

Aside from using a new tight-fitting fibre washer on the petcock mounting screws, about the only thing I have found that will stop a fuel leak on a petcock is Hylomar Blue - a gasket sealant. I'm sure there are other products that also work as well as Hylomar - but I haven't yet found them.

You can get Hylomar at aircraft mechanics' supply places or online. I am told that it was developed by Rolls Royce after WW-2 for use on aircraft turbine engines and it seems to be impervious to fuel, oil, heat...etc., etc.

 

[Jan_P]

Those petcocks don't get so good ratings 3.9 of 5

 

[Niels B]

Even if he does not, hopefully he got them back cause the are still worth $.

yes indeed - would happily take them off his hand

 

[Niels B]

When mounting an XS650 petcock, you really do need to use those special fibre washers that fit quite tightly onto the two JIS mounting screws - and they must fit tight on the screw threads. I have found that an old used washer generally will leak and so I buy them buy the dozen - just in case.

Aside from using a new tight-fitting fibre washer on the petcock mounting screws, about the only thing I have found that will stop a fuel leak on a petcock is Hylomar Blue - a gasket sealant. I'm sure there are other products that also work as well as Hylomar - but I haven't yet found them.

You can get Hylomar at aircraft mechanics' supply places or online. I am told that it was developed by Rolls Royce after WW-2 for use on aircraft turbine engines and it seems to be impervious to fuel, oil, heat...etc., etc.

View attachment 259323

used this to seal old HD engines back in the 70ties + as you all know they would leak from anywhere possible haha

 

[1979Special]

Okay, good notes, folks. Thank you all.

@MaxPete, I'll take it apart and see what it looks like inside. Are you saying it could be leaking from the screw holes instead of the housing? (I suppose fuel will leak from anywhere.)

Looks like I have some work to do this weekend. (In addition to cosmetics.)

 

[1979Special]

I might still have some fuel resistant gasket maker after installing a fuel pump in a Husky, but it's probably all dried out now. If so, I'll look for the Hylomar. Thanks for the tip!

 

[Jan_P]

I have used Permatex and Plastic padding red stuff gasket maker but Hylomar has good reputation

 

[MaxPete]

Okay, good notes, folks. Thank you all.

@MaxPete, I'll take it apart and see what it looks like inside. Are you saying it could be leaking from the screw holes instead of the housing? (I suppose fuel will leak from anywhere.)

Looks like I have some work to do this weekend. (In addition to cosmetics.)

YES - if you stare at the assembly you will see that the mounting screws go right up into the tank and so the fuel will leak right down the screw threads.

So - those fibre washers must fit onto the threads very tightly so that they stop the fuel from weeping down and onto the engine, the exhaust (KABOOM!! ), the ground, your brand-new riding pants, down into your boots ....etc.

However, in my experience, a little dab of Hylomar Blue on the washers will stop that from happening.

Pete

 

[1979Special]

YES - if you stare at the assembly you will see that the mounting screws go right up into the tank and so the fuel will leak right down the screw threads.

Okay, I have a good game plan for this weekend.
Thanks for the detailed info.

 

[ThatXS650Guy]

One thing to remember: almost all repop parts will be inferior to the factory originals. You are better off rebuilding the Yamaha parts than slapping on cheap replacement parts from China.

 

[XSTime]

Watching the video a couple times has me asking are you sure it’s the mount screws that are leaking? The drip volume looks to be more than that.
The left screw had a drip but ?
Could it be the valve body leaking?

 

[Wingedwheel]

Definitely learned my lesson with aftermarket petcocks. I think I’ve taken apart and reworked two sets now. No problems after I put them together properly. Now I prefer to rebuild the stock ones.