Topic: Bypassing vacuum shut off valve. Need help plugging vacuum port.

[Msh5337]

So I'm in the middle of cleaning the carbs on a CB650 I was just given, and noticed that I broke the vacuum port nipple that screws into carb #2. Now being that I'm bypassing the fuel shut off valve, I dont need this anyway. But I'm not sure how to go about plugging this hole. I cant find a screw to plug it anywhere. Would it be a really bad idea to just JB Weld this shut?

[Flyin900]

Unless you replace the petcock the valve wont flow gas since it is designed to open from the vacuum from that broken nipple when the bike is cranked over to start initially or is running. I wouldn't just JB weld it shut since it was a Honda safety feature to ensure the gas won't continue to flow into the engine if a floats sticks and you leave the petcock open. Hydro lock isn't your friend.

Since you have the carbs off just drill out the broken brass tube in the intake runner and you should be able to find a small brass barb adaptor at any automotive shop that will fit into the new port and then JB weld that into place. You can cap the top with a rubber cap that many automotive stores sell in a blister pack kit in various sizes for that specific purpose of capping vacuum lines/ports. This still leaves the option to use the AFV (auto fuel valve ) by you or someone in the future.

You will still need to change out that petcock to a normal style, or work around the internal diaphragm to manually flow gas like a standard style petcock

[Don R]

 My 900c had it bypassed by a PO. Not sure what he did but isn't there a petcock setting that flows without vacuum? If not how would it start with dry carbs?

 Maybe a smaller screw jb welded in?

[Msh5337]

Thanks Flyin, that's a good idea. I didn't know they sold all that at the auto parts store. Well, I have to get a new fuel tank for her anyway as she didn't come with one. So it's all good.

[scunny]

never seen the vacuum one, but isn't there a prime setting (no vacuum needed) ?

[Flyin900]

I should have asked if it has the AFV attached to your petcock, or if it is a stand alone part elsewhere on the carb assembly? No prime setting on the petcock, so some guys just bypass it on say a CB 900 since it is a stand alone piece not part of the petcock assembly.
On other models it is part of the petcock assembly attached directly to the housing and I don't know if you can do a work around on that style. I have rebuilt a number of them since the kit is still available from K&L as an aftermarket piece, so I have never tried to rig the petcock bypass on that's style of unit.
If it is a stand alone piece then with a couple of T adaptors and some short gas hose you can bypass the AFV and just run the petcock as normal. Just remember to shut off the gas when the bike sits.
If your not into doing a repair of the broken pipe then something to plug it will work, although it will remove/render the future use of the AFV system as inoperable.