Petcock with vacuum “valve”

[Niels B]

I refurbished a set of petcocks for my ‘78 that I’m trying to get back in original condition. I however don’t quiet understand the concept and also not sure if it’s better to run with older model petcock that don’t have the vacuum function. If I get this right do the second (vacuum) line got to the manifold with the “air tube “ - cant find a good picture that show how the hoses connect. Any advise?

 

[Jan_P]

If I had the option have no vacuum petcock I would go for that
I even once plugged one that had it to use without the vacuum
There are rubber parts inside that can leak and the hose going to the intake manifold can leak causing a misfire on left cylinder

 

[Wingedwheel]

As far as I know you can run with the No -vacuum style just plug the vacuum barb that the hose for the petcock runs to.

 

[Jim]

I

....and also not sure if it’s better to run with older model petcock that don’t have the vacuum function.

I overhauled my vacuum petcock with OEM rubber bits over 4 yrs ago. Still works good, no leaks.

 

[Niels B]

I replaced all rubber parts too - read about the risk of failing but assume it’s if they sit and dry out from not being used - assume the brass nozzle is the one connecting to vacuum barb on the intake manifold ?

 

[Wingedwheel]

I replaced all rubber parts too - read about the risk of failing but assume it’s if they sit and dry out from not being used - assume the brass nozzle is the one connecting to vacuum barb on the intake manifold ?

That would be the one…

 

[5twins]

I like the vacuum petcocks and will continue to use them as long as they hold up. I've been running them since I refurbed the bike and got it back on the road back in 2005. They still work fine. I did disassemble, clean, and lube them way back then and they've worked fine ever since. Here's the vac line to manifold connection (orange hose) .....

 

[Niels B]

I like the vacuum petcocks and will continue to use them as long as they hold up. I've been running them since I refurbed the bike and got it back on the road back in 2005. They still work fine. I did disassemble, clean, and lube them way back then and they've worked fine ever since. Here's the vac line to manifold connection (orange hose) .....

View attachment 214774

View attachment 214775

Thanks, good to know and nice pic too. Read a lot of horror stories about the vacuum petcock - based on your experience I feel I’ll be ok.

 

[jetmechmarty]

I've not touched my vacuum petcock. It has been working fine since 1983.

 

[wildav]

I wonder if trouble with vacuum petcocks was a production lot issue. My left side petcock went leaky while the bike was still under warranty in 1979. I didn't replace the other side until 2003. No problems since. Generally I drain the tank if it's going sit for a prolonged period. I agree with 5t , I like the vacuum controls. But when one fails beware, when #2 failed I had just filled up for a long Texas middle of nowhere ride and smelled gas then saw it flooding out of the breather box. I was lucky i was close to the barn.

 

[mrtwowheel]

Yamaha must have made a good one. Honda's vacuum petcocks of the same era are referred to as S.O.S. , son of satan.