Fuel taps, vacuum rebuild kits or swap to non vacuum...?

[radxs650]

While getting the '79 XS Standard ready for Spring riding I needed to change a clutch cable which had me pulling the tank off which in turn I discovered a leaky fuel tap.

Two part questions here:

Are the stock, vacuum type fuel taps worth the rebuild kits or are the non-vacuum type taps worth the changeover...? If the non-vacuum type is better, is there anything besides plugging the vacuum ports on the carbs that needs to be done...?

Vacuum type rebuild kits.

Thanks for any insight here.
Rob


https://www.mikesxs.net/petcock-kit-vacuum-200-2014.html?qty=2

Non vacuum type fuel taps

https://www.mikesxs.net/yamaha-xs65...?fits-motorcycle=Yamaha/XS650/all-models/1979

 

[jpdevol]

Personally, I prefer the non-vacuum petcocks - subscribe to the theory KISS. I recently installed a pair of the Mike's non-vacuum on a '75 and they work well; no issues so far......

Capping the vacuum ports on the intakes would be the only step needed if adding to a vacuum model

 

[Jim]

I'm not gonna offer an opinion one way or the other, but If you go the rebuild route I'd recommend against the kit from Mikes.
Mikes rubber bits have a (well deserved) reputation for being crap.... as in only lasting a year or two.

Most, if not all the OEM rubber bits are still available from places like Partzilla. It'll cost a few extra bucks, but I rebuilt mine with OEM bits about 4-5 yrs ago and it's still working as it should.

My SG is the first bike I've owned that has a functioning vacuum petcock. I must say I've grown to like the simplicity of turning the key off and walking away.

 

[jetmechmarty]

I stand with Jim on this. The vacuum petcock is a high quality item. I’ve had my XS650SK for 40 years and 65,000 miles. All I’ve ever done to the petcock is use it. I believe instructions for a proper rebuild live in the tech section. Unfortunately, it’s an easy job to screw up and the correct parts aren’t cheap.

I have an aftermarket manual petcock on another bike. After a simple rebuild it’s working fine. I don’t believe the quality is as good as OE, but it is a viable option. Right and left are not available for your ‘79. Only left. The right side will have to operate backwards.

 

[radxs650]

@Jim
Gotcha however, the parts are not all available from Partzilla. Any other outlets that you like...?

Should I also conclude that I need part numbers 19, 22, 23 & 24...? Diagram below from Partzilla website.

Thanks
rad__



@jetmechmarty,
I have done the fuel taps on my Honda Hawk GTs and Guzzis, I wonder how and why these XS taps can be easy to screw up...?

Thanks,
Rob

 

[5twins]

Many times it's just the rubber disc with the 5 holes in it behind the arm that gets torn up. Often you can just flip it over, presenting a fresh side out for the arm to seal against. Worth a try anyway. Also, check the holes in the back of the arm. Sometimes they have sharp edges and that tears the rubber disc up as you turn the arm. If there are sharp edges, round them off slightly with a small, sharp pocket knife.

 

[jetmechmarty]

I have done the fuel taps on my Honda Hawk GTs and Guzzis, I wonder how and why these XS taps can be easy to screw up...?

There are varying skill levels present. You're indicating that you've BTDT. The o'ring seat should be polished smooth.

Here's a very helpful link about the repair of Yamaha vacuum operated fuel valves.
https://xjbikes.com/forums/threads/rebuilding-the-yamaha-vacuum-fuel-valve-w-pics.25058/

 

[Jim]

@Jim
Gotcha however, the parts are not all available from Partzilla. Any other outlets that you like...?

Should I also conclude that I need part numbers 19, 22, 23 & 24...? Diagram below from Partzilla website.

That's not a vacuum petcock you're showing. Try here...

https://www.yamahapartshouse.com/oemparts/c/yamaha_motorcycle_1979/parts

 

[radxs650]

That's not a vacuum petcock you're showing. Try here...

https://www.yamahapartshouse.com/oemparts/c/yamaha_motorcycle_1979/parts

Ok, I am wicked confused here... The parts breakdown on that yamahapartshouse link; "Fuel Tank, XS650F" is the same as on Mike's. #19, the rubber gasket for the tank to fuel tap is available, the rest are not.

Is that not the vacuum type tap...?

To be honest, I'm not certain that I need a kit, when I mentioned that the fuel was still coming out when I needed to remove the tank, I was advised by @bosco659 that the fuel tap probably needed attention because with the tap in the "ON" position, it should stop flowing with a vacuum type tap.
I think I have that correctly.

Thanks__

This is my tap configuration....

Left...

Right...

 

[jpdevol]

Yours are for sure vacuum petcocks. I'm a bit confused as well; the listings (and I checked CMSNL too) list the tank gasket and 5-hole valve as available, but none of the vacuum partsPartzilla lists the whole petcock as NLA, but CMSNL has them in-stock for $133

 

[Jim]

First, yes those are vacuum petcocks. If it has the "PRI" position, it's vacuum. The PRI position stands for prime. It bypasses the vacuum side of things and passes fuel without the engine running.

 

[Jim]

This is from Yamaha Parts House. It's the '79F
It shows more clearly the vacuum housing on the back, but even it isn't showing the diaphragm in the back housing, just the gasket... 23.
Most strange.

 

[Jim]

To be honest, I'm not certain that I need a kit, when I mentioned that the fuel was still coming out when I needed to remove the tank,

There's one little bitty o-ring that usually causes that. Hang on and I'll see if I can find it......

 

[Jim]

Found it. It's in my resto thread. You could remove the back (vacuum) housing and just replace that o-ring. It's worth a shot.
https://www.xs650.com/threads/jims-1980-sg-miss-september.50545/post-591766

 

[jetmechmarty]

Found it. It's in my resto thread. You could remove the back (vacuum) housing and just replace that o-ring. It's worth a shot.
https://www.xs650.com/threads/jims-1980-sg-miss-september.50545/post-591766

View attachment 243214

View attachment 243215

View attachment 243216

Yes! And polish the seat.


Is this yours? This one has limited parts availability and extra pricey.

 

[radxs650]

Found it. It's in my resto thread. You could remove the back (vacuum) housing and just replace that o-ring. It's worth a shot.
https://www.xs650.com/threads/jims-1980-sg-miss-september.50545/post-591766

Nice,
I'll give that a try. Is there a possibility of causing damage to the diagram in that assembly when popping that housing off...?

With the info on your invoice, I should be able to source the O-rings locally.

Many thanks,
Rob

 

[Jim]

Nice,
I'll give that a try. Is there a possibility of causing damage to the diagram in that assembly when popping that housing off...?

With the info on your invoice, I should be able to source the O-rings locally.

Many thanks,
Rob

The diaphragm is made of rubber impregnated fabric. It's pretty durable. As long as you take the normal precautions it should be OK.

 

[5twins]

I don't think that '79F drawing Jim posted is showing the petcock you have. The Standard and Special vac petcocks differed. The arm and rubber disc behind it were smaller on the Standard version. Also, the fuel line nipple stuck straight out to the rear. You appear to have the Special version with the larger arm and the fuel line nipple coming out at an angle. This is the Standard type on my '78 Standard .....

So, just keep that in mind if ordering parts. You probably need parts for the Special petcock.

https://www.partzilla.com/catalog/yamaha/motorcycle/1979/xs650sf/fuel-tank

 

[radxs650]

Sorry for the delay... long story. Been ridiculously busy elsewhere.

So I am unable to find an issue with the O-Rings in the back of the fuel taps that @Jim talked to me about.

Thinking about going to the non-vacuum fuel taps however, the ones on Mike'sXS seem to have a different base and gasket area are shaped slightly different and suitable for up to'77 only.

This is the base of mine, '79 XS650F...

Mike's...

 

[jetmechmarty]

The one you show from Mike's won't fit your Special. The tanks through 1977 have smaller bolt spacing than the later ones.