V8 Fuel pump question

[Guest]

I have six Studes; five driveable and one under construction. Three are sixes (two flatheads, one OHV) and three are Stude V8 powered.
Only on my 60 Lark with a V8 will the mechanical fuel pump NOT pass gasoline when I'm using the electric pump to prime the system, after it's been sitting a few weeks. I know this because I have a clear filter just before the gas enters the carb. (I know I shouldn't have it there...) While running the pump gas doesn't make it into and through the filter, so I'm figuring back when I put a new pump on the engine at the rebuild, I got one that won't let gas through.

Is this SOP or should I be looking at another pump? I hate over-cranking the engine. Thanks!

[Milaca]

Interesting. If it cant push gas through the pump to the carb, then that inturn should mean that gas can't drain back out of the carb when parked. [?]


Brent's rootbeer racer.
MN iron ore...it does your body good.

[Tom Bredehoft]

There are two check valves in the fuel pump. Both of them open only with flow toward the carb. Unless these are compromised, no fuel can flow the other way. As to fuel draining from the carb, the needle valve is at or above the level of fuel in the float chamber, even with the needle valve open fuel will not siphon out of the carb.

It sounds as if one or both of the valves are stronger than the electric pump. A fuel pressure gage at the carb might be in order.

[img=left]http://www.alink.com/personal/tbredehoft/Avatar1.jpg[/img=left]
Tom Bredehoft
'53 Commander Coupe (since 1959)
'55 President (6H Y6) State Sedan
....On the road, again....
'05 Legacy Ltd Wagon
All Indiana built cars

[Guest]

It turns out my old (sealed) electric pump just quit pumping. Had to find another parts store since my local NAPA folded and bought their's: http://tinyurl.com/yf7j58d
Funny, their tech support said it wasn't 'free-flow' but it is. Took a few seconds to fill the bowl - car fired right up and ran great with the switch to the ele. pump off.


A nation of sheep will beget a government of wolves. - Edward R. Murrow

[Mike Van Veghten]

Milaca -
"If it cant push gas through the pump to the carb, then that inturn should mean that gas can't drain back out of the carb when parked."

Interesting comment, how does gas drain out of a carburetor, without turning it upside-down?

Mike

[DEEPNHOCK]

(Splitting hairs for forum fun and no profit[])
Good point Mike...
And to add...
Fuel does not 'drain' out of the carburetor into the engine.
It is pushed out through the venturi's by higher atmospheric pressure.
Some might percolate out if the fuel is actually boiling, but then it is still being 'pushed' through the passages, whether internal, or external.
(I would love to see or listen in on Smokey Yunick talking to Bernoulli about hot vapor cycle engines 'up there')
Jeff[8D][8D]

quote:Originally posted by Mike Van Veghten
Interesting comment, how does gas drain out of a carburetor, without turning it upside-down?


Milaca -
"If it cant push gas through the pump to the carb, then that inturn should mean that gas can't drain back out of the carb when parked." [/br]

[Milaca]

quote:Originally posted by Mike Van Veghten

Milaca -
"If it cant push gas through the pump to the carb, then that inturn should mean that gas can't drain back out of the carb when parked."

Interesting comment, how does gas drain out of a carburetor, without turning it upside-down?

Mike

My thought was that the fuel in the steel line between the fuel pump and the carb would only retain fuel if the fuel pump held it there when the engine wasnt running. However, if the needle & seat hold tight, it also shouldnt let the fuel escape the infeed line. When my Hawk sits for only a day or two, I have to crank and crank to get it to fire as it seems that the fuel supply isnt there. I dont see any leaks and the lines are tight. Any idea why this may be? I've adjusted the choke and put a new kit in the carb and replaced the fuel pump and it hasnt improved.


Brent's rootbeer racer.
MN iron ore...it does your body good.

[Tom Bredehoft]

Perhaps the high volitility of modern gasoline causes it to evaporate. You drive the car, get the engine hot, park it in the garage, and the heat from the engine keeps the carb hot until all the gas has evaporated.

Yes, the valves in the pump will keep it from draining back.

[img=left]http://www.alink.com/personal/tbredehoft/Avatar1.jpg[/img=left]
Tom Bredehoft
'53 Commander Coupe (since 1959)
'55 President (6H Y6) State Sedan
....On the road, again....
'05 Legacy Ltd Wagon
All Indiana built cars

[Mike Van Veghten]

Milaca -

If you look into the way that part of the carburetor works...your theory falls seriously short.
The liquid (gasoline) level is nearly 1/2" under the needle and seat (on most carburetors).

When you shut the engine off, the fuel level would in most cases be at or very close to the bowl being full. This will keep the needle fairly snug against the seat.

So, for the gas to drain out, the gas would have to, on it's own, form together into a solid stream, then head up to the needle and seat, a 1/2" away...which by the way would now most likely be open because of this gas stream...and pinpoint its opening...and flow thru the seat and out into the fuel line.
So, reading the above short paragraph, really seems very highly "unlikely". At least here on earth.

What is happening to your gas...? It's evaporating. That is, the natural condition of many liquids, is that they tend to form into a gas (nonsolid) and evaporate.
Every carburetor ever produced (that I know of) has a somewhat large "vent" opening or tube so that as the fuel is being pulled into the passages of the carburetor and into the intake manifold, there is no vacuum being formed in the float bowl.
If there were no vent, the fuel would not flow into thru the carbutor and into the engine.

That...is what happens to the fuel level in a sitting engine.
But in a properly setup carburetor, a few weeks or even a month or so, this should not effect the way an engine starts. For most carburetors, it would take a long.......time for the float bowls to fully empty from evaporation.

Mike

[Milaca]

Mike, I wasnt suggesting that the carburetor could drain back through the fuel line, only that the fuel in the line itself may drain back. But Tom B. says a good fuel pump will not allow this to happen, and I believe him. Even if it could drain back through the pump, it would need to suck air through the needle & seat to alleviate atmosheric pressure (although it would still drain out even with the needle seated, just not as quickly). As for the gasoline I am using, I use non ethanol gas in the Stude.


Brent's rootbeer racer.
MN iron ore...it does your body good.