1978 GS1000 carb troubleshoot

[2-Bit]

Just sucked on the vacuum line and fuel started to pour out. I didn't shoot out but it wasn't a trickle either.

[Sandy]

unhook your fuel line, aim it at a bucket. Suck on the vacuum line to turn on the flow. How fast does the fuel flow?
Should be a good solid stream of gas.

I saw somewhere before a number for how much fuel per minute should flow. Does anybody remember where? Mine seems to be working properly and I'll have my tank off tomorrow for a carb sync, if I remember I'll measure mine. Might be a handy number to have.

[2-Bit]

Considering the tap was on the on position and seemed to flow fairly fine, I tend to think that the tap is working at least ok. I will try some dry gas in the tank to cure possible water/fuel issues but other than that I am starting to feel a bit lost. Seems like is a fuel issue but not sure. Spark plugs will be replaced tonight to rule out a problem there. Will let you know what they look like after the switch if the engine still decides not to work. Thanks and all suggestions are appreciated.

[2-Bit]

Finally got the bike home and removed the tank to further troubleshoot. Changed the plugs and drained the old gas and replaced it with new gas. Sucked one more time on the petcock before I reset the tank and could barely get a trickle. Now just testing my patience until the new one arrives. Thanks for the help and will get back to ya when I get the thing installed.

[Sandy]

OK, I did the test with my tank and got a flow of 1 quart in 40 seconds with the petcock on prime and the same results with the tap set to on and reserve while sucking on the vacuum line. The test was also the same with or without the gas cap installed to see if the cap vent was working. To simulate a plugged vent I sealed the fuel inlet with my hand and noticed substantial flow reduction by the 1 cup level. This was done with a tank about 1/3 full with the proper 7mm fuel line attached but not connected to the carbs. If you don't get these numbers about the only things that could be wrong are the petcock screen plugged or dirty (clean it), plugged fuel cap vent (disassemble and clean it), bad vacuum line (replace it) or the petcock itself needs servicing or replacement. If the vacuum diaphram in the petcock is shot you'll see fuel in the vacuum line or taste it if you do the vacuum test above before looking and you'll need to replace the petcock. I've heard most people have had problems with aftermarket rebuild kits so you may just want to get a replacement from Suzuki or a Pingel. Before replacing though I'd try disassembling your petcock first to see if it just needs to cleaned or if something is making it stick shut, nothing to lose there but about ten minutes of your time.

[2-Bit]

Wow, thanks Sandy. Seems as if I have a project after work today. Well done!!!