Fuel tank breather function - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 2 (permalink) Old 04-06-2011, 03:50 PM Thread Starter
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Fuel tank breather function

Anyone know how the breather on the fuel tank works inside?
I recently pinched my breather line on the tank, and implodded my tank. Got a new one on ebay, but before I get it painted and installed back on. Was just wondering if anyone knew how it breaths from inside the tank? I can feel and see the overflow tube inside the tank and see how it works, but not the breather tube which I can feel. Just dont know how it functions, which it does now! This happened by removing the flapper valve and evap canister, and pinching off all the lines(ALL Lines). Dumb I know! When I f*ck up-I f*ck up good!! Poor tank couldn't breath, got it on video but you can only hear it not see it. Loud pop like a back fire, but didn't realize it till it came back inside(Winter Michigan). Stared in disbelief for about 5 minutes, costly repair after saving some $ on doing my own valve adjustment. Which was within specs after 16,544 miles, so for anyone interested. Don't waste your time and $ with a 16,000 mile valve check, EVERYONE'S gonna be just fine till around 25,000. I've done alot of mods this winter-Correctly&Tastefully! But dont smoke and modify-the medical anyway!! lol
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post #2 of 2 (permalink) Old 04-06-2011, 07:57 PM
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The fuel tank breather is just a pipe that extends from near the bottom of the tank to near the fuel filler inlet.
It allows the tank to equalize with ambient pressure as fuel is used, or if fuel expands/contracts when hot/cold.

On California bikes, the tank breather does not vent to air, but is routed to the Evap canister to trap the fuel vapors.
Then when the engine is started, it purges those vapors to the throttle bodies to be burned.

The overflow tube is near the vent tube location at the bottom, but extends up to the filler neck. If the tank is overfilled, the excess fuel is drained down the overflow tube to the ground.
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