I am a latecomer to this discussion, but if you genuinely do have a vacuum diaphragm to stop fuel with the engine off, then this sounds /highly/ plausible. I say this not because I feel you're a liar (I don't!), but simply because I'm not familiar with petcock fuel systems and their operation.
But if you have a vacuum line from a fuel valve to the manifold, and the diaphragm in that valve is torn, that's undoubtedly how you'd end up with fuel flooding the engine, rather than through the carburettors. I have heard something incredibly similar, wherein a forumite on an aircooled forum had a boost-referencing pressure regulator. The diaphragm inside was leaking, so he was constantly running rich. He corrected it with programming, but when he replaced the regulator with a new part he was suddenly so lean the engine wouldn't start. Confused the hades out of him and his father. Totally sounds similar to the issue here. -Kurt On Sat, Aug 14, 2010 at 7:04 PM, Allen Thomas <[email protected]> wrote: > Gene, I was thinking about this; I agree that it is highly improbable that > the needle valves would rot to the extent that fuel would bypass them to > such a great extent. Here is another more plausable scenario. the torn > diaphragm in the petcock could allow fuel to pass it and drain straight down > the vacuume line directly into the #2 intake runner, bypassing the carb all > together. this would fill the cylinder, and fuel would eventually drain past > the rings into the crank case. If you started the bike in this condition > it could hydrolock the engine. Even a little gas in the oil will destroy its > viscosity, and prematurely wear the berrings and transmission gears. The > reason I made such a strong warning is that I think this is a new member, > and he may not be aware that this condition could occur. I'd hate to see > another new member loose his bike prior to getting it on the road. Let me > know your thoughts. > > On Sat, Aug 14, 2010 at 6:13 PM, Allen Thomas <[email protected]> wrote: >> >> I guess the problem would be that if the rubber in the diaphragm is rotted >> to the point it leaks air then the rubber tips of the float needles could be >> rotted enough to allow fuel past them. >> >> On Sat, Aug 14, 2010 at 6:06 PM, Allen Thomas <[email protected]> >> wrote: >>> >>> This forum isn't the only place where I have read that horror story >>> either. >>> >>> On Sat, Aug 14, 2010 at 6:05 PM, Allen Thomas <[email protected]> >>> wrote: >>>> >>>> It shouldn't, but it obviously has for at least one member. >>>> >>>> On Sat, Aug 14, 2010 at 6:03 PM, Gene Henry <[email protected]> wrote: >>>>> >>>>> Will someone please explain to me why the float/needle(s) in the >>>>> crab(s) does not stop the flow of fuel when the engine is not running, but >>>>> does when it is running? >>>>> 12" of head (height of the fuel column) = about 1/2 psi. The >>>>> float/needle should handle that. ???????????????????? >>>>> >>>>> Inquiring minds want to know. >>>>> >>>>> Gene >>>>> >>>>> >>>>> >>>>> ----- Original Message ----- >>>>> >>>>> From: Allen Thomas >>>>> To: [email protected] >>>>> Sent: Saturday, August 14, 2010 4:49 PM >>>>> Subject: Re: [Nighthawk Lovers] Re: Digest for >>>>> [email protected] - 13 Messages in 5 Topics >>>>> Since you filled the tank, make sure you close the petcock when not >>>>> running! otherwise you could fill the crankcase with gas, ruining your >>>>> oil, >>>>> and potentially destroy your engine or worse! >>>>> >>>>> On Sat, Aug 14, 2010 at 5:10 PM, surfswab <[email protected]> wrote: >>>>>> >>>>>> > im thinking i will pull the petcock and clean it or replace it.< >>>>>> >>>>>> Good plan. You'll probly find the diaphragm rubber torn/worn out. It >>>>>> keeps a fuel valve open when vacuum's applied (engine running) and >>>>>> closes the valve in the absence of vacuum (engine not running). >>>>>> >>>>>> If it's malfunctioning, it allows raw gas to gravity feed to the float >>>>>> bowls -- overflowing into the intake, cylinders, air box and >>>>>> crankcase, causing a real mess. >>>>>> >>>>>> Rebuild kit's about $20. New petcock about $150. Add new plugs, new >>>>>> oil, new air/oil filters and several hours of draining/mopping/sucking >>>>>> raw gas/oil from everywhere it's not supposed to be. >>>>>> >>>>>> Don't ask me how I know all this. >>>>>> >>>>>> -- >>>>>> You received this message because you are subscribed to the Google >>>>>> Groups "Nighthawk Motorcycle Lovers!" group. >>>>>> To post to this group, send email to >>>>>> [email protected]. >>>>>> To unsubscribe from this group, send email to >>>>>> [email protected]. >>>>>> For more options, visit this group at >>>>>> http://groups.google.com/group/nighthawk_lovers?hl=en. >>>>>> >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Nighthawk Motorcycle Lovers!" group. >>>>> To post to this group, send email to [email protected]. >>>>> To unsubscribe from this group, send email to >>>>> [email protected]. >>>>> For more options, visit this group at >>>>> http://groups.google.com/group/nighthawk_lovers?hl=en. >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Nighthawk Motorcycle Lovers!" group. >>>>> To post to this group, send email to [email protected]. >>>>> To unsubscribe from this group, send email to >>>>> [email protected]. >>>>> For more options, visit this group at >>>>> http://groups.google.com/group/nighthawk_lovers?hl=en. >>>> >>> >> > > -- > You received this message because you are subscribed to the Google Groups > "Nighthawk Motorcycle Lovers!" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/nighthawk_lovers?hl=en. > -- You received this message because you are subscribed to the Google Groups "Nighthawk Motorcycle Lovers!" group. 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