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Old December 6th, 2018, 09:27 AM   #69
ducatiman
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Name: Gordon
Location: new york
Join Date: Sep 2009

Motorcycle(s): '95 DUCATI 900SS/SP '07 DUCATI SS800 '19 HONDA CBR650R

Posts: A lot.
MOTM - Nov '18, Mar '17
Quote:
Originally Posted by dodgerdad View Post
I think you're on to something in relation to the petcock. I've done some searching and have found many posts & videos which display the exact issue I'm having resulting from a bad petcock (diaphragm). Oddly, it seems more prevalent in Harley/twin cruisers but they describe the same symptoms (hanging idle at low rpm, running rich, bogging under rapid acceleration, inconsistent idle when coming to a stop, etc.). Recently when I've removed my tank I always find a decent amount of fuel in my vacuum line (I assume this is abnormal).
Fuel within the vac line indicates a torn, ripped, pinholed or otherwise damaged, unable to seal diaphragm (within the petcock). The diaphragm is activated by engine vacuum (on the back side of the petcock) and when activated, allows gravity fed fuel to flow (on the front end). The 2 functions are separate, the diaphragm should absolutely NOT be not allowing "leakage" between front and rear sections. I've also encountered them MISSING return springs within petcocks, lost or discarded? Gotta look inside.

Its a vac leak, but sucking unmetered fuel, air or an intermittent mix of both, whacking the mix in the LH cylinder out. MUST deal with this...may very well be the underlying issue.

Darn....now knowing fuel is present in the vac line...I wish you had sent it (the petcock) with the carbs.

Either a new, confirmed good used, or a rebuild of yours is definitely called for. And testing thereafter, can easily be done on the bench.

If you have any doubts doing, send it on, labor on me.
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gordon@customcarbservices.com
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Last futzed with by ducatiman; December 6th, 2018 at 09:40 AM. Reason: added info
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