engine vacuum/fuel delivery via petcock '79 GS1000

[aaronc70]

Hello, I'm working on my father-in-law's 1979 GS1000 (I believe it is a GS1000E, the VIN is GS1000517606). I think the engine/carb vacuum is not puling enough and will not consistently keep the vacuum petcock open. The bike runs OK after first starting but a few minutes later it begins stalling out. Sometime is will idle, but if I open the throttle, it dies (even after engine is warm). I notice this more when on an incline. If I disconnect and suck on the petcock vacuum line, fuel flows back into the carb and it's fine for a minute or so, but then goes back to doing the same thing.
I ordered what I thought was a replacement, mechanical petcock: https://www.ebay.com/itm/New-Petcock...53.m2749.l2649
It looked very similar, but the mounting holes were too narrow so it wouldn't bolt up.
Looking at the parts fiche, I can't tell what exact petcock I have. The repair manual talks about a "prime lever", but my stock petcock has no switches, buttons, levers or dials. No way to "open" it except for pulling vacuum. The valve seems to work fine, even if I only apply a little bit of vacuum, fuel flows.
My questions:
1. what is the part number of the petcock I have?
2. Can I replace it with a regular petcock, with an off/run lever? If so can someone provide a link or part number for one with the correctly spaced mounting holes?
3. If I measure vacuum on the carb, how much should it be?

Thanks for any and all help!

r,
Aaron C.

[aaronc70]

Just double checked the part number. It's listed as 44300-44011 although the picture in the diagram does not look like my vacuum petcock.
Maybe this is the correct one: https://www.ebay.com/itm/New-Fuel-Pe...VXYO:rk:1:pf:0
I may have just screwed my part numbers up.

[Guest]

I wouldn't use that 14 dollar petcock. OEM is best, but kind of pricey. I put a K&L on my 1980 GS1000L, and it works great. I'm not sure what particular one your bike uses, but there's a wealth of petcock info on this site. Use advanced search and "titles only".

[Nessism]

From what you describe you have a 1980 model year bike (or at least the tank) with the leverless petcock. The bolt center is 50mm for that model petcock and a petcock with a lever won't fit because it will hit the top of the carbs. If fuel flows when you pull a vacuum then the petcock is fine. The running problems you are experiencing is elsewhere. Maybe the fuel tank vent is not working properly? Tank full of rust? Not sure. You may want to check the Newbie Mistakes thread linked in my signature to see if anything applies.