wierd starting problem... xr650r

Was wondering if anyone has seen this before...

I had just finished riding down a set of bumpy railway tracks, right as I left the tracks, the bike started to sputter, I switched to reserve and the bike sputtered a bit more and then died. Looking at the level of gas (Clarke natural tank). I could tell I was right about the normal level when I hit reserve. Left the petcock in reserve and tried to start it... no luck. My first thought was maybe some crap got into the carb so I opened the drain on the carb to see if gas came out. Sure enough gas came out so I figured it was not fuel related. My next thought was maybe an electrical connection came loose....

Fast forward about 1/2 hour, still no luck and a buddy had towed me to the nearest rode where he went to get his truck. While I was waiting I decided to trouble shoot a bit more. I was going to take the tank off, disconnected the gas line , quickly turned the petcock to reserve expecting to see gas flow out, but nothing came out ???

At this point I cracked the filler cap and looked in the tank and could see some small bubbles coming from where the petcock was. replace the cap, turned the reserve on again, sure enough gas came out.

Connected everything up again and sure enough bike runs no problem:applause:

My question is, what could have caused this, I have run onto reserve several times before with no issues, it appears there was some type of air bubble in the line that was trapped and until I opened the cap it wasn't letting fuel out.

I have a breath vent on the cap??

Any ideas..



Sounds like you had a vacuum formed in your tank, but that would usually only happen if the vent like was crimped or blocked.

If your vent line was open / unblocked - beats me.

What size is the Clarke tank - does it use a fuel pump?

I would venture to guess that the 'check valve' in the vent lodged shut when you were going over the tracks. When you unscrewed the cap, the check valve freed up, allowing the tank to vent properly. The problem was most definately vacuum in the tank. I would remove the petcock and completely clean it, and then get a new one-way vent hose, as the one you have may have some dirt in it that is fouling the venting mechanism.

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