Carb losing fuel over night.

  • Thread starter Deleted member 1959
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D

Deleted member 1959

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Hi guys
My LeBaron is now running again and has a new Carter BBD (Chinese copy...)
However, it now takes a long time to start it from cold like alle the fuel disappears over night from the fuel line.
It didn´t have this problem with the old Holley 2280 lean-burn carb.

The fuel pump is new, and the vapor canister is still in place.
Most fuel and vacuum hoses have been renewed.
I have been running on 95 oct with 10% ethanol, but am switching to 98 / 5%.

My mechanic was aware of this and recommended I install a non-return valve on the fuel line. While it´s an easy solution, I am not convinced this is the root of the problem, since the old carb did not have this problem.
I have taken some pictures of the engine bay, in case anyone can spot a problem.

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Aspen500

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If the carb bowl itself goes dry overnight, it can't be the fuel pump since the fuel line is above the fuel level. It's either leaking into the manifold from the bowl somehow or the fuel is boiling out of the bowl, which can happen with a carb and today's fuel made for high pressure efi. Do you have a thick carb to manifold gasket or is it a thin piece of paper? A thick one insulates heat from the carb and reduces fuel boiling. If fuel boiling is the problem, a heat shield between the bowl and manifold can help.
 
D

Deleted member 1959

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Just checked the gasket.
It seems he was aware of the problem since he put 3 gaskets on top of each other - 2 thick ones and 1 thin paper-like one. In total about 8-9 mm.

Yesterday I put hose clamps on all the lines going to and from the vapor canister, and this morning it started up first time after about 14 hours of standstill. So maybe there was a slight leak there ?
 

AJ/FormS

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The vapor canister collects vapors from the tank and from the bowl. There is a signal line coming from the carb that will open the purge valve, and finally, the purge line will then send the vapors up to the carb, at the command of the signal line.
To prevent stalling and driveability issues; the signal line has controls on it.
You cannot purge when the engine is cold. You cannot purge at small throttle openings The purge must be variable in delivery.

But the thing I want to highlight is the purge valve. If it fails in the open position, or if the line from it to the carb leaks, or your signal line is not functioning correctly;
you will have starting issues.
If the purge-line sucks air, you can expect long cranking times, requiring addition choke to overcome, and after the choke is off, the engine will want to stall.
If the purge line purges all the collected vapors, the engine will be rich during first cranking in the morning. Together with the choke, the engine might become flooded. Later crankings will not find fuel vapors and the problem sorta goes away. But since the carb is purging full-time, you will still have low-rpm driveability issues.
I'm not saying this is your problem, but it is just something to check out.
 
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D

Deleted member 1959

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The vapor canister collects vapors from the tank and from the bowl. There is a signal line coming from the carb that will open the purge valve, and finally, the purge line will then send the vapors up to the carb, at the command of the signal line.
To prevent stalling and driveability issues; the signal line has controls on it.
You cannot purge when the engine is cold. You cannot purge at small throttle openings The purge must be variable in delivery.

But the thing I want to highlight is the purge valve. If it fails in the open position, or if the line from it to the carb leaks, or your signal line is not functioning correctly;
you will have starting issues.
If the purge-line sucks air, you can expect long cranking times, requiring addition choke to overcome, and after the choke is off, the engine will want to stall.
If the purge line purges all the collected vapors, the engine will be rich during first cranking in the morning. Together with the choke, the engine might become flooded. Later crankings will not find fuel vapors and the problem sorta goes away. But since the carb is purging full-time, you will still have low-rpm driveability issues.
I'm not saying this is your problem, but it is just something to check out.
Hi AJ
Once the engine is started, it does not stall, and I dont have low-rpm issues. So far so good.
Where is the signal line ? I have a new Carter BBD, and it has no electronics on it.
I dont know about the purge valve either. Is it part of the carb or the canister ? I have seen other pics of canisters with an extra valve house on top, but mine does not have that.
 

LSM360

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I get three days max on my edelbrock 1406 on my Power Wagon 360, and have to pour gas down the carb. 93 octane/10%. Incredible how quickly the fuel bowls dry out with today's crap fuel.
 

Aspen500

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If my Aspen sits for more than 3 or 4 days, I have to crank, crank, crank,,,,,,pump the throttle, crank, crank, another throttle pump and varooooooom. Overnight, it fires instantly. That's with a Summit 4 brl carb. Modern fuel made for injection just vaporizes (evaporates) too easy if it isn't under pressure. Think water starting to boil at 212 degrees at sea level vs boiling under pressure at maybe 240 or 250 degrees. Even more if the pressure is high enough. Same basic thing applies to gasoline.
 

AJ/FormS

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In gasoline there are over 14 different fuel molecules each with a different boiling point. The lightest boils at 95*F, the heaviest at 395 or something.And in-between are many different boiling points. If it boils at 95, you can imagine at what temp it begins to evaporate.
The lightest are in there, it is said, to help light your engine off.
The heaviest are like adding mix to your bar-drink, it slows things down.
But I suspect there is/are profit related reasons to put the very light and the very heavy molecules in our gasolines.
Gasoline, outside the combustion chamber, requires a very limited AFR to lite off; if too rich or too lean and it won't lite. Each of the different molecules has it's own characteristics. After two or so days, the lightest VOCS in your vented carb are gone, and what's left is difficult to light... plus the liquid level is now lower in the bowl, making "pull-over" harder.
You gotta understand that the carb does not suck gas.
The piston,falling on the intake stroke, creates a low-pressure area in the cylinder, which the higher pressure atmosphere then tries to fill. Air always moves from a high pressure area to a low pressure area.
As the air is moving thru the venturi/throttle bore, atmosphere is also pushing down on the fuel in the fuel bowl.But with the liquid level in the fuel bowl now lower than design, and the fuel itself now heavier, there comes a point where the atmosphere can no longer push the heavy fuel to the top of the idle wells, and so even if you could start it with enough pumpshots; until the liquid level comes up, the choke blade and venturis will not provide enough pressure differential, especially the 1bbls, to sustain running, and the engine is being forced to accept the syrup before any good stuff gets there.
If your car sits in the sun for hours, it's just so much worse.
Your fuel will benefit from installing fuel-stabilizer. Up here in Canada, Shell gas is advertised as having it added, and I find shell 87E10 to be better than other brands.
Underhood heat is also an enemy of the carb. I run fresh air into my carb, and I pop the hood when I pull into the gravel-floor carport, on the North side of my 2-story house. It's always so much cooler under that roof.
As for me:
As others have mentioned, I too keep a small bottle of stabilized, 5% 2-cycle mixed gas, under the hood.... just in case. I mix the oil in there to help maintain the ring-seal during cranking, to help the rings create the high pressure differential, that will encourage the atmosphere to get the heck moving. That's another reason I have an 11/1 Scr engine. And I run a Holley DP carb. It has TWO accelerator pumps, NO choke, and a dash-mounted, dial-back, ignition timing box with a range of +6/-9. So I rarely have problems.
And finally, your engine has a carb heating system on it, that forces hot exhaust gases to move from one exhaust manifold, to up under the carb,and to then exit into the manifold on the other side. The thing that causes this to happen is usually called a heat-riser valve.It's job is to be closed when the engine is cold, to help the cold-engine run better, and to open as the engine warms up. Well, they tend to seize up and if this happens at any other position than wide open, then the hot gasses tend to cook the carb, making it run hotter than it should. Then when you shut the car off, the hot carb boils it's gas away.
 

Hayzoos

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On Sunday, I pulled the top off my carb after the car was parked hot midday in the sun and sat overnight. In the process I activated the accelerator pump and hardly any fuel squirted. When I got it open I could see less than half maybe down to a third the capacity in the bowl. The only other explanation would be a leak in the bowl. But, I do believe the fuel evaporates.

I am now considering an electric fuel pump so I do not have to crank over excessively to fill the bowl.
 

Justwondering

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Today ... I cut the top off a small empty coke bottle, cleaned it out and filled it with gas.
Poured the gas in the carb so I could get the engine started after 2 weeks of sitting.
Started up just fine.
Prior to that, it was crank crank crank and pump pump pump on the pedal.. to no avail.
Then the carb/engine ran fine for 45 miles.

JW
 

jd340

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On Sunday, I pulled the top off my carb after the car was parked hot midday in the sun and sat overnight. In the process I activated the accelerator pump and hardly any fuel squirted. When I got it open I could see less than half maybe down to a third the capacity in the bowl. The only other explanation would be a leak in the bowl. But, I do believe the fuel evaporates.

I am now considering an electric fuel pump so I do not have to crank over excessively to fill the bowl.
Did you end up fitting an electric pump? I'm tired of having to crank and crank to fill up the bowl too. Thanks
 
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