Fuel starvation issues

[Guest]

On Friday it broke down on me while on my way home from work . Started to lose power like I was out of fuel so I switched to Reserve. Continued to gradually lose power while on the highway (still able to maintain 60 mph, but obviously struggling to) and then I pulled over and it died.

Info on the bike:
-1982 GS750E, 41k miles
-Carbs cleaned Winter 2015
-Petcock rebuilt Winter 2015
-K&N pods, 4-1 header, DynoJet Stage 3
-About 600 miles since the work was completed

I had no problems before Friday. Even going to work that morning, the bike seemed perfectly fine. I filled up the bike the previous day, and my normal ride to work is 40-50 miles. I estimate the bike went about 100 miles before I had this issue.

After I pulled it over, I drained the bowls to find that cyl #1 & 4 had very little fuel, 2 & 3 had plenty. I have an inline filter installed that showed no debris. After I drained the bowl for cyl. #1, I put the petcock on prime and #1 immediately started flowing fuel. So the lines/passages seem unclogged and there's plenty of fuel left in the tank.

So, I primed the bowls again, and it started. It died on me about a half a mile later, so I left it on prime. The rest of my ride was 40-50 mph back roads so I took it easy (light fuel loads) and I did have to stop a couple more times because it started acting like it was starved for fuel again. Left it idling for a couple minutes and it would be good to go again.

So far I have ruled out:
-Rust/debris - tank is clean, no debris in filter, fuel seems to flow fine when on prime
-Clogged fuel feed - filter is clean, carbs 2/3 had full bowls, bowl 1 filled immediately when on prime

I'm thinking collapsed fuel petcock when under vacuum? I used the rebuild kit from Z1 Enterprises FWIW.

[tom203]

"I'm thinking collapsed fuel petcock when under vacuum?"

good thinking, petcock rebuilding is iffy- get new petcock from Z1 - and skip the inline filter as it's not needed with a good petcock filter.

[eil]

Also check that the gas cap is venting properly. If it isn't, a vacuum will build up in the tank. You can tell that's happening if you remove the cap and hear a hissing sound.

[nicolettijd]

I have this problem intermittently on my GS1100EZ. Occasionally I have some hissing when taking off the gas cap, and the cap is clearly worn. How does one go about fixing a sealing gas cap?

I've ruled out the petcock being the issue, and just recently cleaned out the carbs as well. I also have trouble with the engine running lean and slowly overheating after about a half-hour of riding.

[chef1366]

I have this problem intermittently on my GS1100EZ. Occasionally I have some hissing when taking off the gas cap, and the cap is clearly worn. How does one go about fixing a sealing gas cap?

I've ruled out the petcock being the issue, and just recently cleaned out the carbs as well. I also have trouble with the engine running lean and slowly overheating after about a half-hour of riding.

You do not need to seal it
You need to unseal it.
Venting is important to the flow of gas.
Clean it
Oh and put a larger main jet in it/Shim the needle or get a jet kit. You will kill this motor if you don't.

[nicolettijd]

It turns out it was my petcock. There was a leak in the vacuum seal and it was pulling gas into the vacuum line. I'm amazed it started and ran. I managed to seal the vacuum line, stick the petcock into reserve after installing a shut-off valve in the gas line. It should work until I get a new petcock.