1980 GS550L won't flow fuel in prime position

[Guest]

Hi,
I rebuilt an abandoned 1980 GS550L, and replaced the unusual two position, no handle petcock with one by K&L from Dark Horse Motors (honestly, someone had disassembled it and I thought there were parts missing because I couldn't find the lever!). I also removed the fuel tank fuel level equipment along with the stock gauges. But I cannot get gas to flow to the carbs in the prime position. If I cheat and drip fuel into No. 1 cylinder, i can get her to start and then she flows fuel under vacuum and runs fine. But if she sits, I have to do it again. I am wondering if the tank lacks a vent that might have been provided by something in the fuel tank sending unit mounted to the tank underside? Or just a bad replacement petcock? Thanks for your help.

[Big T]

The vent is on the gas cap, not the sending unit

[tom203]

Does this new k&l petcock look like this? Any screwdriver slot on it anywhere?

https://www.ebay.com/itm/Fuel-Petcock-Suzuki-GS550-GS750-GS850-GS1000-GS1100-1980-81/312399093683?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20131003132420%26meid%3Dde75f8acea834c2ea53dcdd086bd6f48%26pid%3D100005%26rk%3D3%26rkt%3D12%26sd%3D191730512735%26itm%3D312399093683%26pg%3D2047675&_trksid=p2047675.c100005.m1851

[mtb1098]

That's the one I bought.

[mtb1098]

I have tried the petcock in both the prime and run positions, but no flow. I can suck on the tube in Run and get some fuel to flow, but nothing on prime. That's why I was wondering about a blocked vent.

[tom203]

I have tried the petcock in both the prime and run positions, but no flow. I can suck on the tube in Run and get some fuel to flow, but nothing on prime. That's why I was wondering about a blocked vent.

If it works like the stock unit, there is a screwdriver slot on side facing out, this has a horizontal and vertical position.....does this k&l have one??

in prime spot, you have to give it a blip of vacuum to get it going....brief press of starter should be enough

[mtb1098]

Never thought of that!! Thought it would just flow. Thanks, will try it when I get back to the bike.

[Steve]

Yep, the stock (dreaded) '80 petcock required what Tom describes as "a brief blip of vacuum". Once vacuum is applied, it will keep flowing, unless the floats are good enough to stop the flow or the tank runs out of gas.

If there is a screwdriver slot, as in the stock unit, the RUN position is with the slot horizontal. PRIme is with the slot vertical.

.