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Old 12-11-2010, 11:58 AM   #1
Chris B.
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Default Fuel Disapearing

The age old problem that I still don't have a definative fix for. Any thoughts would be appreciated.
My stock 35 Ford 21 stud can sit for a week and start no problem but any longer and the gas dissapears from the carb and it won't start unless gas is poured down the carb. I had to pour gas down 8 times this time. I have replaced power valve and have new fuel pump and rebuilt carb. I don't want an electric fuel pump as I think this is a bandaid treatment to a problem that didn't exist when the car was new. I also want to keep it correct. I have checked the float bowl in the past and found it right empty. I have heard of many solutions previously but I think most are theoretical. If the fuel disappears, it can only be from two places , the power valve or back down the line thru the fuel pump. Has anyone actually fixed the problem?

Last edited by Chris B.; 12-11-2010 at 12:00 PM. Reason: Spelling error
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Old 12-11-2010, 12:14 PM   #2
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Default Re: Fuel Disapearing

Chris B: Robert Shewman in Pa. makes a fuel line flex hose with a built in check valve which will solve the problem of drain back. I ordered one for one of my cars and it really makes a difference. Robert has ads in the V-8 Times. Hope this helps...Tom.. Mr Shewman"s email address is [email protected]
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Old 12-11-2010, 12:17 PM   #3
ford1
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Default Re: Fuel Disapearing

the fuel cannot be sucked out of the carb by the fuel line draining back past the fuel pump, the needle and seat is to high above the fuel to cause a siphon effect, so if not past the power valve it has to be going past the jets or is just evaporating, even if you do have a new pump my guess its got a bad check valve and letting the fuel flow back to the fuel tank and the pump looses its prime, if your not going to drive the car for a while, remove the carb, set it on your work bench , fill it full of gas and check on it often and see if you can find where the gas is going
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Old 12-11-2010, 12:28 PM   #4
ken ct
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Default Re: Fuel Disapearing

You say "new fuel pump" most if not all NEW PUMPS are being made in china,does that tell you something.I would suspect FP get a rebuilt one from a good rebuilder,other than that i would suspect carb. Depends where you got that too.There are some hackers out there.I just opened one up and you wouldn.t believe the junk he put back in there.Looked pretty outside ,inside was a disaster. this should be a #48 stromberg to be correct for a 35. ken ct.
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Old 12-11-2010, 01:14 PM   #5
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Default Re: Fuel Disapearing

Quote:
Originally Posted by ford1 View Post
the fuel cannot be sucked out of the carb by the fuel line draining back past the fuel pump,
Even though the fuel can't be sucked out of the float bowl, it can drain clear back to the gas tank leaving the pump high and dry and, unless the pump will pump air, make it hard to refill the carburetor bowl after the fuel has evaporated out of it from sitting too long.

I think the check valve either just before or just after the pump may help keep the pump "primed" so that, even if the fuel is gone from the bowl, it can be quickly refilled and start.

Of course, if the pump is working right, it has it's own check valve that should prevent back flow. It would seem that the pump may be defective if it's allowing fuel to drain back.

One more thought. A very small leak in the fuel line from the tank to the pump would admit air while sitting to allow the fuel to flow back as well. No check valve, either in the pump or otherwise would prevent that. I've had that before. Such a small leak would not be detectable under normal operation because the fuel in the line from the tank to the pump is under vacuum such that it wouldn't be pushed out of such a leak. But, if such leak is low enough in the line, it might be found while just sitting. But, if it's high, like just before the pump, you'd have to actually pressurize the line while full of fuel to find it.

My 2 cents.
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Old 12-11-2010, 02:18 PM   #6
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Default Re: Fuel Disapearing

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I think it evaporates out of the carb. One thing that will help is after shutting the car off, pull the choke completlly out...
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Old 12-11-2010, 03:00 PM   #7
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Default Re: Fuel Disapearing

you have not mentioned the carb type if you have a stock 35 you have the Stromberg 48 ?
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Old 12-11-2010, 03:07 PM   #8
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Default Re: Fuel Disapearing

It shouldn't evaporate in 1 week,mabey 2 weeks but not 1.Be nice to know what engine and carb he has??? ken ct .Are these old original lines including the flex hose ot the firewall??
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Old 12-11-2010, 03:17 PM   #9
richard crow
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Default Re: Fuel Disapearing

remove carb take the top part off fill the bowl. put cover back on. put carb on a flat piece of carboard or wood or glass. let it sit check every day to see if it gets wet. if it don,t get wet remove top of carb & see if float bowl is empty. if it is & the surface you had carb siting on is dry. then the gas is evaporting. don,t forget when you shut off the eng the heat will aid in the evaporing.once the fuel is in the carb bowl even linda lovelace cant suck it out of the fuel line fiting on the carb.the niddle valve shuts that off if the float is down a little it will let air pass remember the float chamber is vented
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Old 12-11-2010, 05:27 PM   #10
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Default Re: Fuel Disapearing

Flex hoses have been a problem for the past few years with the new gas causeing the inner tube of the hose to come apart and suck air. The check valves in the fuel pumps never worked very good even when the cars were new. Read the test procedure in the Ford Service Bulletins. "With a gauge on the carb line shut the engine off and the fuel pressure should not leak back to zero in less then 2 minutes". What's that tell you?? Bob Shewman makes 2 modles of new flex hoses that are not bothered by the new gas or any gas that will come along in the future. One hose is like the standard flex hose and the other is has a check valve that works built into the hex fitting on the pump end of the flex hose. I have used these for almost 2 years on several cars and my flex hose and fuel drain back problems are history. G.M.
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Old 12-11-2010, 07:05 PM   #11
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Default Re: Fuel Disapearing

All good ideas posted above. However, If your carb bowl/power valve leaks to empty after 2 or 3 weeks, never pour gas down the carb. Dangerous. Get a small plastic bottle with a needle spout on it (I use one that comes with my wife's hair color kit) and fill it with a few ounces of gas and inject it into the open pipe in the carb throat to fill the bowl. Then put your air cleaner on and start the engine. Safe this way.
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Old 12-11-2010, 07:37 PM   #12
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Default Re: Fuel Disapearing

My 50 Ford and even my original 50 bought in 1960 did the same thing. The current 50 has had quality carb, fuel pump and flex hose repair. I use the hair color bottle/air tube fix if the car hasn't been run for over a week, it starts just fine then. Check Sallys Beauty store for the bottle, they are cheap. I have had an electric fuel pump in a box under my desk for 3 years . It hurts less to use the little bottle than it does to get under the car. Bob
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Old 12-14-2010, 10:24 PM   #13
Chris B.
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Default Re: Fuel Disapearing

You say you haven't had any fuel drain back problems for two years. Did you test to see if the power valve leaked any fuel out of the float bowl? How long can the car sit and still start without any problems related to fuel?
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Old 12-14-2010, 11:30 PM   #14
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Default Re: Fuel Disapearing

Quote:
Originally Posted by G.M. View Post
Flex hoses have been a problem for the past few years with the new gas causeing the inner tube of the hose to come apart and suck air. The check valves in the fuel pumps never worked very good even when the cars were new. Read the test procedure in the Ford Service Bulletins. "With a gauge on the carb line shut the engine off and the fuel pressure should not leak back to zero in less then 2 minutes". What's that tell you?? Bob Shewman makes 2 modles of new flex hoses that are not bothered by the new gas or any gas that will come along in the future. One hose is like the standard flex hose and the other is has a check valve that works built into the hex fitting on the pump end of the flex hose. I have used these for almost 2 years on several cars and my flex hose and fuel drain back problems are history. G.M.
I'm not sure how the flex hose can drain a carburetor bowl??
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Old 12-15-2010, 01:51 PM   #15
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Default Re: Fuel Disapearing

Unfortunately this phenomenon seems be what 90 percent of old ford have .I did some tests on a 36 fuel pump we rebuilt with a 3ft plastic hose connected into a jar of gas, two compressions of the hand on the pump arm pulled the gas up lickty split.you do need a good quality pump kit.make sure you are getting the full stroke of the push rod ,The correct 35 pump has a 2/3 piece valve were you cannot replace the seat, not like the 36 that has a valve all in one ,So if your valve seat is worn you will have excessive drain back .there may be a way of repairing by polishing the seat by using something like tooth paste .You could sit the carb over a jar and seal it over the whole think with cling wrap and then watch it over a day or so to see were the gas is going. In my esperance they need a drink more than a skirt's bottle gives,You could set up a clear hose back to the tank to watch the percentage of drain back also .
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Old 12-15-2010, 02:07 PM   #16
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Default Re: Fuel Disapearing

If things work great in every other respect, I'd put in an electric fuel pump to "prime" the carb before starting and probably a fuel regulator and keep pressure at say 1 1/2. I know this does not "solve" the problem but I hate to mess with things that work well in all other aspects.
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Old 12-15-2010, 02:24 PM   #17
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Default Re: Fuel Disapearing

I have had the same problem with my 46 for years, tried another fuel pump, changed carb, nothing worked, I was told by a old ford man
that the fuel evaporates, especialy during warm weather, through
the vent tube inside the carb, so if my car sets longer than 2 or 3
weeks, I refill the bowl through the same tube and it starts fine, I can remember as a young boy my father had a 48 ford and if it sat long
he would have to prime the carb, I would get to start the car as he
poured a little gas in..
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Old 12-15-2010, 03:10 PM   #18
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Default Re: Fuel Disapearing

filling like that works ok on the later holly/Ford carb but not on the early one ,The doesn't seem to be a issue on some others makes such as Chevs because the pumps is low on the moter. AS a Boy we to poured gas down the carb like you , we worked 700 milels away from home .To re leave boredom we worked on our fords at night with a lead light out the window of our quarters .These were cars we picked up of Farms .One time I was worked the starter while my dear dad poured Gas down the carb ,and it spat back and blew gas all over him ,on fire he ran down the car park slapping his back, it went out ,All I could do was laugh it was the funniest thing to see .
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Old 12-15-2010, 03:20 PM   #19
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Default Re: Fuel Disapearing

Had the same problem with my 42. The problem startded after a couple of years driving it.

It was the Flex hose that had cracked let the pump suck air.
Causing it not ot work.
A new Flex hose, Problem solved.

I dont like the idea of electric pump in series with Ford original pump.
If the membran cracks or some or ther problem you will fill the engine with raw gas (that's Petrol in UK ;.) )

Had a 39 ford that emptied around a gallon a week without trace.
It was the rusted out steelfuel line that got soaked and let gas evaporate without leaking on the ground.

So keep you fuel lines in good order and your Ford will start quick and easy.
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Old 12-15-2010, 07:19 PM   #20
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Default Re: Fuel Disapearing

When you shut the engine down the manifold and carb are very hot. Gas evaporates from the heat and even more evaporates over two weeks of sitting. With a bad flex line and poor check valves the fuel in the pump and fuel lines drains back to the tank and it is almost impossible to start by cranking without starter fluid or gas down the carb. The gas in the carb can not drain back to the pump or tank. With a good flex hose,tight connections and a working check valve, fuel is trapped in the pump and lines and in 4 or 5 revolutions of the engine gas is pumped to the carb and it starts. The fuel in the pump, flex line and supply line are like a straw stuck in a glass of coke, pull the hose out of the soda and the soda drains out of the straw. Hold your finger over the straw and the soda stays in the straw when lift it out of the glass of soda. The check valve is the same as your finger over the end of the straw, in this case the check valve is your finger. G.M.
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