Petcock repair

Hello, Just a quick question about the petcock on my 86 VF500. When I test my petcock should it hold vaccuum? The reason I ask is I was running without the vacuum source (it broke) using a handheld vacuum pump to open the petcock. I noticed it would not hold a vacuum so I had to keep applying vacuum to keep the carbs filled. I just want to make sure that it is not supposed to hold vacuum. If it is supposed to hold vacuum then I guess I need to rebuild it.
Thanks,
Jim

 

Help! Do I need to take the petcock apart? I would really like to get this on the road this weekend.

 

It needs to hold vacuum otherwise it's creating an intake leak or sucks gas. It probably needs a rebuilt or a better assembly.
If the vacuum loss is not too much maybe it's not worth messing with a rebuilt.

 

I thought so.
I took it apart and the diaphram was dirty but intact. It seems to work fine with no leaks. I think I'll leave it for awhile.
Thanks blitzas
Jim

 

The valve won't necessarily hold vacuum indefinitely, but the better job it does the better it will work. Don't be immeditely alarmed if the vacuum slowly drops when testing it like you describe.

You might consider trying this too:

Daugherty Motorsports - Tank Valve Petcock Modification

 

Hello Jamie,
Yeah, I came across your mod when I was doing my research. I've been riding the bike and it is working OK but I noticed a little bit of a lean surge and my idle is too high so I don't think I fixed my vacuum leak issue at the petcock. Either that or it's somewhere else which is entirely possible. I'd like to keep the vacuum feature for now if I can. I have a KZ400 and have forgotten to turn the gas off a time or two only to find gas all over the garage floor the next morning. The wife hates that.
Thanks for the tip,
Jim