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Old November 14th, 2021, 11:53 AM   #32
CZroe
CPT Falcon
 
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Name: J.Emmett Turner
Location: Newnan, GA
Join Date: Apr 2009

Motorcycle(s): '08 CP Blue EX250J, '97 unpainted EX250F, 2nd '97 unpainted EX250F (no engine), '07 black EX250F

Posts: A lot.
Quote:
Originally Posted by Triple Jim View Post
The vent should be free to let pressure in or out pretty quickly. They do get clogged though, and if the vent gets partially blocked it might let enough air leak in to let the engine run, but not fast enough to prevent a vacuum if you get a sudden cooling situation. It's not designed to be partially restricted like that though.
If the vents were totally unrestricted then Kawasaki Tank Whistle™ wouldn’t be a thing. The tank vents just fine for normal conditions. It’s only when I do something that specifically gets the tank hot and then rapidly cooled that the vacuum starves the carbs/engine of fuel.

My 2008 Ninja 250 was brand new when I first experienced it and it continued whistling for years so I know the vent wasn’t clogged. I didn’t figure out what it was until it happened twice a year later (remember: riding daily). In both cases, opening the cap allowed it to run… but one instance was during a downpour and I had to push to a covered gas station. It was left warming up so that I could try to beat the rain but my relief at work was nearly an hour late with my bike left running the whole time. The engine was totally hot while the bike was stationary and all that heat was going up into the tank. Sure enough, the rain immediately started pouring on me (and the tank!) as soon as I left and a couple blocks later I sputtered out at a stop light.

The other time was after I blasted up the interstate, engine piping hot, only to park and blast off again a short while later. I was just checking a Goodwill store and was probably in there around 10 minutes. Once cool air was flowing over the engine and tank I sputtered out at a stoplight a few blocks away.

After that, well, it was easy to predict what situations might cause this and I could open the tank preemptively or predict that it would soon sputter out. Even before then it would only happen one in several hundred rides (pushing 1,000). It’s no wonder the issue flies under the radar. After all, the tank does vent normally.

After seeing it affect at least two others here over the years I feel I should point it out any time I see a possibly relevant situation.
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