Re: IML: Fuel Siphoning

[Crownking <crownking62@xxxxxxxxx>]

Mikey etal:

We have had reports of unvented gas caps causing everything from repeatable short range driveability followed by stalling to tank collapse.  Both of these phenomena occur because the fuel pump pulls a vacuum on the system as it supplies gasoline to the carb and sucks against an obstructed vent. I implode my tank on my '62 after having spent a fair amount of cash and time repairing thousands of little pin hole leaks when the vent line from the tank was blocked by vermin (mud dobbers).  The fellow that raised the issue indicated he got a whoosh upon removing his gas cap.  Sounds to me like he has a vacuum due to either the wrong cap or a plugged vent or both.  A vacuum in the system would certainly cause fuel to be sucked back into the tank at least until the vacuum broke.  I would be surprised if he is driving this car very far without collapsing the tank if this is indeed his problem, though.

 

Regarding fuel volatility, I can assure you that the refining industry has spent billions since '90 REDUCING volatility to meet the Clean Air Act Amendment's RVP specs.  The only exception to the significant decrease is for those blends that included alcohols to meet the oxygenate requirements.  Thanks to a pandering Bob Dole and a politically motivated EPA, alcohol blends got a 1 psi break on the volatility spec.  Despite the break, I would be surprised if even today's gasohol has a higher vapor pressure than pre-90's gasoline sold during the same season. Yes, vapor pressures are blended to meet seasonal driveability requirements.  In many states/locales maximim seasonal vapor pressures are prescribed by law, too, and those specs are always decreasing.  I know of no increase in allowed RVP in any locale in the country during my years as an environmentalist.  Not one. 

 

mike and linda sutton <mikanlin62@xxxxxxxxxxx> wrote:

> Today there was a post about fuel siphoning back thru the needle and seats 
> after the car was shut down. It did not mention whether is was a Holley or 
> Carter carb, but since this is the Imperial list, we can presume it is an 
> Imperial and probably an AFB or a Holley, at the long shot a thermoquad. 
> Before going any further, it is not my intent to start a flame war or a 
> peeing match about this, and that I do in fact respect the person who made 
> the post and that Im not disputing their knowledge or experience.
>
> Having said all that, this has been cussed and discussed , peted and 
> repeated many times on this list. The general complaint is the excessive 
> cranking required in some Imperials before they will start, and is generally 
> attributed to lack of fuel in the float bowls. The causes , in no 
> particular order , have been attributed to heat soak
>  after shut down causing 
> fuel to boil off in the bowl, leaks from porosity or cracks , and the 
> difference in todays fuels versus the fuels of the past in how easily the 
> evaporate.
>
> Now, my question...HOW can fuel siphon back thru a needle and seat after 
> shut down. The needle and seat are higher than the level of fuel in the 
> bowl and once the fuel pump was to stop pumping, the column of fuel 
> contained in the line to the needle and into the bowl would cease to be 
> filled completely full , which would not let a siphon action occur. Also, 
> the check valves in the fuel pump should stop it from flowing backwards any 
> further than the pump. I cant believe that there are that many Imperials 
> running around with fuel pumps with this condition. I have analyzed this 6 
> ways to Sunday and I just cant get there from here. This should be in the 
> archives, so feel free to dispute me all you please, I just want to see an 
> explanation for this
>  phenomenon.
>
> I know the problem is real enough, it happens on my 62 now and then. I have 
> installed opaque fuel filters in the line to the carb and watched the fuel 
> in the line before. There is always a bit of an air pocket in the filter 
> when I shut the car off, but the level never drops down completely. That in 
> itself dispels the siphon theory as far as I can see
>
> Ok, inquiring minds want to know??
>
> Mikey
> 62 Crown Coupe 
>
>
> ----------------- http://www.imperialclub.com -----------------
> This message was sent to you by the Imperial Mailing List. Please 
> reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be 
> shared with everyone. Private messages (and attachments) for the
> Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx
> To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm

---

Yahoo! Mail
 
Stay connected, organized, and protected. Take the tour