Hello friends,
I have very old car its Daihatsu Charade 86 Model, I am facing this issue since few months. Sometimes when i park the car for 2 or more days then try to start it, it doesnt start. I noticed that fuel filter was empty, then i pour some petrol from the top of the carburetor, car starts and fuel filter is getting petrol from fuel tank. And when i tried to suck the petrol through pipe from the filter it fills full but just when i stopped sucking the pipe, petrol is started to draining from filter to fuel tank.
But when car starts by pouring the petrol on carburetor it doesnt create problem until i stop it for 2 or more days.
Sorry but I think you have a leak in the bottom of the carb so that the fuel drains out of the carb bowl when it sits. Sometimes there is a plug on the bottom that can be resealed with epoxy or you may need a new carb. The carb has to come off for inspection though.
OP could possibly place a clean white towel underneath the carb and check for drips from time to time. Even with evaporation there should be some residue in the towel if there is a leak.
Sound like the carburetor float bowl is draining of the car sits too long.
Normally, this is prevented by a check valve at the fuel pump that prevents fuel from flowing backwards through the feed line. Sounds like yours is leaking. In a fuel injected vehicle, as long as the injectors are closing fully there’s no way for air to get into the system and the fuel can stay in the line like Coke stays in a straw by putting your finger on the top of the straw. But on a carbureted engine, air can get into the bowl through the orifice through which the fuel is normally drawn into the carburetor body by the engine’s vacuum, and the fuel can easily drain past the float bowl’s needle valve back through the line to the tank.
In short, the fuel is draining back to the tank.
Try putting the key to the ON position for three or four seconds before turning it to the START position. If I’m right, that’ll give the pump an opportunity to refill the float bowl and the engine should operate normally. It’ll also provide fuel in the bowl for the accelerator pump to “prime” the engine before starting, a necessary function with carbed engines.
I believe this car has an electric fuel pump so the fuel pump should refill the carb if you switch the ignition on and wait a little while before cranking the engine…
Simple. The needle valve is designed to stop fuel from flowing INTO the bowl (when the bowl is full) not to stop fuel from flowing OUT OF the bowl. If the float is not at the very top and providing pressure on the needle, the valve will allow passage beck into the feed line, and since air can be drawn back through the open orifice through which the fuel is normally feeding to the carburetor throat when the engine is running, without the check valve at the pump preventing it the fuel can simply drain back down.
Bottom line, the float & valve system is designed to prevent fuel from flowing INTO the bowl (when full), not out of it! If it were allowed to flow freely into the bowl after the bowl is full, it’d push through under pressure into the carb throat and flood the engine.
That’s a major difference between carbs and fuel injection. In fuel injection, fuel is forced through an orifice under pressure into the engine, in carburetors the engine is drawn into the engine from a little bowl of fuel solely by the vacuum created by the pistons during their intake strokes. The float and valve are only there to allow the bowl to be kept full without pressurizing.
In order for the fuel to be sucked back out of the float bowl, the needle jet would have to be submerged in the gasoline. Most of the carbs I’ve seen have the needle jet on the top of the float chamber and the liquid falls into the float chamber like a waterfall. If there was reverse flow, the needle jet would only suck vapors back into the tank.
Like I said, leaky plugs in the bottom of carb bowls was a problem with some carbs some years ago. Sometimes the plug could be epoxied but other times the casting needed to be replaced. Never had one myself. Also the case could be porous allowing the gas to drip out into the intake manifold over a couple days. I suppose too there could be a gasket failure but don’t think there is gasket below the float. Having no idea what this car is, sure have no idea what the carb looks like and it would be interesting to know if it actually does have an electric fuel pump versus the mechanical one. I guess the other issue might be a lazy fuel pump just being noticed now and the leaky carb could have been that way for quite a while.
Edit: The last carb I worked on was my lawn mower and the latest book I have with a carb is for 1958 but the pics confirm the needle valve inlet is above the bowl. Think about it. If the inlet was not above the bowl, how would the fuel drop into the bowl? Now a toilet tank fills from the bottom under water pressure, but not any of the carbs I’ve seen. So there is a leak somewhere somehow in my view but the thing has to come out for inspection. But I think its all academic anyway since Elvis has left the building.
The gas could be boiling out of the bowl. My brother solved this on his '51 Packard by adding an “outboard motor fuel primer bulb” between the tank and the fuel pump.
I’ve never had one apart, but I still don’t understand how the fuel in the bowl can siphon back when the fuel level is below the float needle valve.
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