Monday, Aug 14 2017 [5,543 miles]
A week ago my bike stuttered and stopped on the way home from an after breakfast ride. The symptoms were the same as running out of fuel. After playing with the petcock including 15 or 20 seconds in the “prime” setting the bike started. All seemed well from that point on. Today I spent some time trying to find a cause.
Fuel line
Filter
Because the bike started after playing with the petcock I thought I’d start there. No fuel flow without vacuum. That’s a good thing. I applied some vacuum to the petcock and fuel began to flow. That’s also a good thing. I pulled the in-line fuel filter and checked for blockage. It was mostly clean. Hmmm.
I grabbed a container with the idea of emptying the tank. I stuck the fuel line in the container and set the petcock to prime to let fuel flow. After a minute or so I noticed the flow had diminished. Ah ha! I cracked the fuel cap and heard the hiss of equalizing air pressure. It’s a venting issue.
Breather Valve
Canister
California bikes vent the tank through a charcoal canister. I put the fuel cap back on the tank and disconnected the vent line from the breather valve. Switching the petcock to prime resulted in good fuel flow. This time the flow did not diminish.
So either my breather valve or charcoal canister is suspect. I’m guessing the breather valve. I dicsonnected the line between valve and canister at the canister and checked for air flow. It wasn’t as free as I expected. However, I’m not sure my expectations are correct.
If the issue happens again (and I expect it will) I’ll disconnect the line at the canister to isolate the breather valve and see if that resolves the issue. If so I’ll replace the breather valve. Otherwise I’ll take a closer look at the canister.