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No fuel with vacuum petcock to on.. diaphragm?

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My new-to-me 400S only runs with the petcock set to PRIME. No leaks, no gas smells, but no zoom zoom noises or go-fast-ness when set to ON, only silence. :D

 

I assume the diaphragm is torn, and thus assume it would be introducing a small vacuum leak into the motor. I get a slightly high idle at times too. It settles down if it give it a sharp stab of throttle, but it made tight trail riding this weekend awfully!  

 

Once I get a chance to *really* clean the bike up, I'll introduce him to you guys. He seems nice enough.

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The tube that is used to create the vacuum could be loose or have a hole in it causing the loss of vacuum  and make the bike run lean.

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The tube that is used to create the vacuum could be loose or have a hole in it causing the loss of vacuum  and make the bike run lean.

Cool, I'll check that tomorrow.

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Also possible the petcock has been modified so the vacuum OFF does not work.  Result is a OFF/ON manual fuel valve with no reserve.

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Winner winner chicken dinner. Begs the question.. it was tucked up out of the way behind the petcock. I'm guessing that it popped off with a tank removal and wasn't properly replaced? Anyway, easy fix ever. :) Can't test right now because neighbours.

 

Thanks chums!

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