66-3X2 442

I would like to get some opinions on a problem that I've noticed on 66 A-Body cars. It seems that the fuel drains back to the tank or at least part way back after the car sits for a few days. You have to crank on it for a while to get the fuel back up to the carb. The fuel does not drain back if the car(s) are cranked or driven on a daily basis. In 66 there was a line restrictor placed in the return line back to the tank but was not used in 67. This drain back problem is on both cars with or without a return line. This problem may be on other year models but since I'm dealing with a couple of 66's with this problem,that's all I can go by. This problem is on a 66 3X2 and a 66 330 4V and the 4V carb has had the well plugs epoxied. Any opinions or help would be greatly appreciated.

young olds

If it has a qjet some filters has little one way valves in them, I believe them to be to counter act fuel drain back but may be wrong.

Tedd Thompson

Your problem maybe due to evaporation of our alcohol tainted fuel.I feel this is what is happening to my car,others have also complained in the past with the same problem but with differant year cars....Tedd

RandyS

My car does exactly the same thing. The carbs have recently been restored to new condition, so I'm pretty sure they are not leaking down. With the fuel inlet at the tops of the carbs, I don't see how the fuel could flow back down to the FP. Evaporation is about the only other possibility........

gs72

The check valves in the fuel pump will not let fuel drain back to the tank.

Fun71

Siphon action, that's how.


The volatility of gasoline was reduced in 1989 and then again in 1992, so today's gasoline (including E10 and E15) evaporates slower than the gasoline these cars used back in their heyday.

Now if you live in a cold climate then your winter fuel is much more volatile than summer fuel, so if you have a tank full of winter fuel then it very well may evaporate fast during the heat of summer.

nsnarsk65cutlass

Agreed,any none fuel injected will do this especially in CA.

m371961

I think it has to do with methanol. I don't understand how fuel would siphon through a needle valve from a vented fuel bowl with the air gap even if the needle is open.
But I ain't no expert.

66-3X2 442

I talked to a good friend this morning who has been a carb guru since the 60's. He says there is a check valve in the fuel pump but the ethanol fuel is killing it and allowing the fuel to siphon back to the tank. He thinks most of the fuel pumps we are buying are old stock and not ethanol compatible and it's ruining the check valve. He says he has seen a lot of this on the older cars. If siphoning isn't a problem,why is there a check valve in the pump? He doesn't know what the answer is as to a fix.

gs72

Without the check valves the mechanical fuel pump will not pump any fuel. If you have ever diagnosed one with a stuck open valve, the fuel pressure gauge just bounces up and down. This is because the fuel is either being pushed back and forth between the pump and the tank or the pump and the carb. It depends on which valve is sticking open. I agree with the ethanol theory. It plays hell with my motorcycle carbs.

RandyS

This might be true if there were a tube leading to the bottom of the fuel bowl, but it simplly comes in at the top of the bowl, with no tube to the bottom to allow siphoning. The check valve in the pump was to keep the fuel in the fuel line to the carb from siphoning back down

gs72

http://www.secondchancegarage.com/public/535.cfm

TripDeuces

There can't be any siphon action with the fuel level in the bowl lower than the fuel inlet needle and seat. I also don't see any evidence of a line restriction on my fuel line and I don't have a return line (66 330 4v). Unless fuel is leaking past the well plugs the jets will always be covered under fuel and the accelerator pump is also full as it's less likely to evaporate because it's covered by the pump cup/seal.
I understand that the newer fuels can evaporate faster due to alcohol content but to have a bowl go completely dry in a couple/few days I find unlikely. You could test this and prove it to yourself with a small juice glass about an inch deep full of fuel just left open to the air for a few days. You're talking a lot more area exposed to evaporation in the juice glass than the 3/8 inch vent tube on the top of the carb.

I think I can answer the check valve question this way. Mechanical pumps are notorious for not being good at pulling fuel. They excel at pushing fuel but for this to happen you need head pressure in the pump to make that happen efficiently. That head pressure needs to be on the pressure side of the pump to allow it to work correctly. If the fuel drains back you have the pump trying to push air which compresses (unlike fuel (liquid)) and that doesn't work well because it gives to much and reduces the pumping action substantially. This is the reason for the one way check valve. Anyone who has a well pump for their house that uses a foot valve (one way check valve) has probably run into this problem. If you lose that column of water from pump to foot valve, pressure side, you'll lose all your pumping action. Then you have to manually refill the pressure side to get the pump working again.

66-3X2 442

Are you talking about the line restrictor I was referencing in my statement? If so,it's only used on cars with a return line and it goes in the return line by the pump.

TripDeuces

I was Mike. I guess that's why I don't have one because I don't have a return line.

Now I'm wondering why Olds would put it on 3x2s and not the other engines?

I'm thinking your fuel pump check valve is damaged, probably from the newer fuels. It still makes no sense you have hard starting problems after a few days though. As long as you have the accelerator pump full and the jets covered the car should start as normal. As you know carbs don't work on fuel pressure but on atmospheric pressure. The fuel pump just keeps the bowl full. It's been a long time since I've had my 3x2s apart but I know that center carb is similar to a 4bbl in operation. They also have well plugs but a different configuration than a QJet so they can leak also. I've seen accelerator pump cups made out of rubber, nitrile and leather. I'm not positive if the alcohol in the newer fuels effects leather but it does on the rubber ones so that could be something to check.

66-3X2 442

If you look in the PIM in section 8,page 2.2 figure 1 you will see the restrictor I mentioned. It says 4V cars only and I only mentioned the 3X2 car because he's having the same problem. It could be the drawing was printed and not revised because the tri carb option was a late addition to production and they also got it. There has got to be a reason for the hard starting due to lack of fuel. I'm leaning toward siphoning in the lines and evaporation of fuel from the carb due to the ethanol in the fuel.It makes sense that fuel in bowl can't be siphoned back through the inlet but the 4V car I mentioned shows signs of that happening. I'm not in on the 4V car work,it's in NC but a reputable tech is and that's what he says it happening.

tru-blue 442

Mine is doing the same thing. 66 400 with a/c and a return line. Single 4 bbl Q-jet.
Fuel pump is probably 6 yrs old.

Koda

Some quadrajets have leaky bowls, not many though.

I think some fuel is going back down past the pump and is leaking around it,
which may or may not be a problem per design (the pump overcomes this during running.)

The checkball may help. However, I like how it takes 7 seconds to start
or so when totally cold. Think of the oil pressure you are building up before
it fires. I kind of like that idea.

BlackGold

Based on my observations of the QuadraJet on my daily drivers, there is a definite correlation between ambient temperature and whether or not there's much or any fuel left in the bowl after the car sits in the parking lot all day at work. In other words, most of the fuel is evaporating, due to both the engine temperature at shut-down and the ambient temperature.

Your mileage may vary.

toymobile

Put an electric pump at the tank. PROBLUM SOLVED

66-3X2 442

Really?

MDchanic

Actually, yeah.

I don't necessarily recommend it, as it adds expense and complexity to fix a problem that may just be due to a porous hose or a leaky check valve, but it will fix it.

This is done all the time with antique cars that sit a lot. One way is to just connect the pump to a momentary pushbutton switch: You press it for a few seconds before starting if the car has been sitting, then crank, start, and run off of the car's own fuel pump.

- Eric

m371961

So there is no problem with the mech pump pulling fuel through the electric one? Does it matter if the elec pump is a bellows or gear type?

MDchanic

No problem with the mechanical pump pulling through the electric pump, or with the electric pump pushing through the mechanical pump.

As for the type of pump, I've only ever seen one kind: the good old kind that goes BRRRRRRRRRRRR like a jackhammer when it runs. It has to be a pump that uses two check valves to operate (as most reciprocating pumps do).
You can hear the electric pump load up when the float bowl is full and the gas stops moving.

- Eric

TripDeuces

Still don't understand why a bad fuel pump is being associated with hard starting assuming you have fuel in the carb bowl?
If you want to check if the carb is leaking remove it and place it over a paper towel on your workbench. Have it up in the air about two inches. You can make a cheap stand out of bolts and nuts. Make sure the carb bowl is full of fuel and watch it for a few days. If nothing leaks onto the paper towel you can eliminate the carb as the problem.

Don't forget that secondary wells can leak also, not just the primary.

MDchanic

I don't think we've actually established whether there's fuel in the float bowl or not at this point.

Seems to me everyone is speculating wildly in an information vacuum.

- Eric

66-3X2 442

I was pulling his chain. I think I'm fully aware of an electric fuel pump and what they do. These cars ran for years without these problems,so trying to find a solution for it without screwing up fully restored frame off cars without resorting to fixes like adding an electric pump is what I'm after.

MDchanic

I agree. It shouldn't be needed.

(Though a lot of restored '30s, '40s, and '50s cars, which came with much less effective fuel pumps from the factory, do have these intermittent pusher pumps for faster starts, and in case of vapor lock during parades).

- Eric

Fun71

I agree that if there is fuel in the bowl, then the engine will fire up.

When I bring mine out of hibernation at the end of the summer (yes, it is garaged during the summer and driven all winter), I pour a bit of fuel into the bowl vent and it fires right up; otherwise, I have to crank it forever to get fuel to the carb. This is obviously a condition where there is no fuel in either the carb or the fuel lines. Adding some fuel to the bowl results in immediate start-ups.

m371961

My 65 with the 4-jet (G?) series carb has no or little fuel in it if it has not been started for 2 weeks, I assume the fuel evaporates.
I never tried using an electric pump with a mech pump.

MD, the bellows type go BRRRRRR, the gear type goes GGGGGRRRRRRRR and requires a regulator.