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fuel emptying from whole system

3K views 24 replies 11 participants last post by  DANGERXY 
#1 ·
My 351 XY has a 600 Holley, stock mech. pump. If I don't start it every 5 - 7 days fuel evaporates from the bowls and drains back as far as the fuel pump.
It may be going back past the pump as well as it takes an awful lot of cranking and sometimes won't get fuel up by itself.

Mate suggested that fuel may be siphoning out of system into fuel tank.
There are no leaks anywhere and no evidence of fuel dripping out of boosters or throttle shafts while sitting. Even the filter is empty.
The car has a vented cap and vented standard tank.

If I start it every 5-7 days it starts first crank usually.

Has anyone had any similar dramas?

Thanks Northey
 
#3 ·
I used to have the same problems years ago when i ran a 302c and 600vac. If i didn't start it for a week, it was real real hard to get going. I have never had this prob with the BG carby, but did allways have an electric pump too. Maybe brenx is onto something.
 
#4 ·
A number of times now I've removed both sight screws after the car has sat for a week and both bowls are empty. The acc. pumps don't even have fuel in them.
To save all the cranking I use a squirter to fill the front bowl until the pump will squirt and then the car starts easily.

The acc. pump works ok. As soon as the throttle is touched fuel squirts.

I've looked few times at around five days and there is some fuel in bowls but no sign of fuel weeping on gaskets, etc. Everything around inside and outside of carby is dry.

I understand that it can drain back to the pump because of a faulty valve but that volume of fuel (2 bowls, lines and filter) then has to go somewhere else. BTW the fuel pump doesn't leak either. Not externally anyway.

Cheers
 
#6 ·
Powervalve is new, gasket not torn or damaged.
It's not boiling fuel. The car is not being driven at moment and it only gets run until engine is starting to warm up. That is when temp gauge starts to move. I can still rest my hand on block after running.
 
#8 ·
Couldn't reply earlier - computer not running well. Mate, been there done that. No fuel dripping from boosters.

That's why I got interested in the siphoning theory. Even if the carb were leaking, that doesn't explain the filter being emptied. If, as Brenx suggested earlier, the 1 way valve in pump failed, that means the fuel has to return to the tank. Is that possible?

Know it seems unimportant but its a right royal pain in the dot having to remove shaker, air cleaner, etc and fill a fuel bowl so I can start car every week.

Any suggestions welcome.
 
#9 ·
northey said:
That's why I got interested in the siphoning theory. Even if the carb were leaking, that doesn't explain the filter being emptied. If, as Brenx suggested earlier, the 1 way valve in pump failed, that means the fuel has to return to the tank. Is that possible?
It's more than possible. It's a reality. I've seen it happen with my own eyes. The car I saw doing it had a fuel filter between the pump and carb. Not exactly the best place to put the filter but it'll do. Due to the filter being their I could watch the fuel drain back. It'd just bubble away and drain.
 
#13 ·
northey said:
No, there's no sign of fuel leaking into engine.
K Then. Thought you may have a leaking fuel pump diaphragm.

Do you have another fuel pump to bolt on?

A inline check valve are a cheap try at around $9 from bursons/repco.

Its strange that it takes a long time for it to drain.

You could fit an electric pump.... :priest:

Has the engine backfired at all since the problem started?
 
#15 ·
TTNOS8 said:
K Then. Thought you may have a leaking fuel pump diaphragm.

Do you have another fuel pump to bolt on?

A inline check valve are a cheap try at around $9 from bursons/repco.

Its strange that it takes a long time for it to drain.

You could fit an electric pump.... :priest:

Has the engine backfired at all since the problem started?
I think it would save a lot of mucking about if I just buy a pump and replace oldie.
I know it's hard for all of you with 2,000,000 hp to understand but I've got to stick to mech. pump. Thanks for help everyone.
 
#16 ·
if you could put a small on/off tap ( steal one off the victa ) in the fuel line you could tell for sure if it was draining back to the tank.
:driver:
 
#18 ·
that is a pain man, how can the fuel leave the bowl?
surely it cant evapourate?
i don't think it can come out the way it came in either coz as soon as the level went below the pin valve, it would stop siphoning...

it could be very slowly coming down the idle holes? They are lower than the main jet so they can siphon...
most stock carbys have a valve in the idle passage that shuts with the ignition off to prevent run on (diesling), this would also prevent fuel dripping out of the idle holes with engine off...
Does your holley have this valve?
If it does, take it out, apply 12v and the pin should pop into the valve, remove 12V and pin should pop back out...

Fuel probably should drain out of filter but wouldn't be a problem with fuel in bowl...
 
#20 ·
It doesn't have that valve. This is both bowls on 600 v.s. holley; it has rear metering plate not jets also. Mate had same problem; yeah it's a pain 'cos it means pulling off shaker every time I start it.

Could be little green men; every time I put a spanner or part down they hide it on me. I'll catch one of 'em one day and paint him purple.
If it were leaking you would think that at any time during the week I could find fresh fuel stains or damp spots inside or outside of carby but there isn't any.

I'll keep looking. Cheers all.
 
#21 ·
Have You Tried Pressurising The Tank, See What Happens
Also Doing The Same To The Fuel Lines In The Other Direction And See Where To Fuel Goes, Might Be An Idea Then You Can Find Out A Way To Stop The Fuel Draining Away Like An External Fuel Swith Like 351cid Said, Better Than Filling Up The Bowls Every Week
 
#23 ·
I had the same problem on the XD with the std Carter Thermoquad vac sec. After no use for a week would have to crank it for ages to get the fuel up before it would start. Garage is at top of steep hill so I used to clutch start it to save the starter & ring gear.
Had two different fuel pumps on it and same problem. I think it just evaporated.

No problems with electric pump installed and Edelbrock carby
 
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