Carburetor without fuel

[elmer]

Hello everyone,
I have a problem and I know how to solve it....
when I am 15 days or more without starting my M151 A2, it starts up well but after a few seconds it is stopped because the carburetor runs out of gasoline.
At first I thought that the gasoline evaporated from the carburetor and solved it by injecting a little gasoline into the tube that goes to the carburetor. This way it works perfectly.
Today I realised that as soon as the engine starts, the gasoline pump takes about 15/20 seconds to pump fuel into the carburetor.
I think that must be the problem I have but I don't know if it's normal and how to solve it.
Thanks a lot for your help
elmer

[rickf]

Pull your dipstick out and see if you have more oil than normal and also if the oil smells like gasoline. If this is the case the fuel pump is bad and the diaphragm is leaking gas into the crankcase. It will also be pushing gasoline up the vent tube into the air cleaner so that will need to be drained and refilled with oil. If no gas small in the oil then it could be a plugged filter sock in the tank, a leaking return valve in the fuel pump, A cracked line from the tank to the pump and that includes the metal line inside the tank. And if you have an inline fuel filter between the pump and the carb that could be clogged. Once you get it running then shut it off and take the line off of the carburetor and have someone crank the engine with the ignition switch off and watch how much gas comes out of the line into a can. There should be good strong pulses of gas. If just weak trickle and you have an inline filter do the same thing before the filter and see if it is better. Let us know what you find after doing those tests.

[elmer]

Thank you Rickf, I will do everything you have told me and I will keep you informed.

Before I forgot to say that once started with the help of adding gasoline to the carburetor if I have not used it for more than two weeks or started without help if I use it weekly, it works perfectly and there is no fault

elmer

[rickf]

A failing fuel pump can keep running even though it is pushing gas into the crankcase and air cleaner. On a civilian car the vent hole on the side of the pump is open to the air so you see the gas leaking right away and know there is a problem. But with the fording vent on the 151 pump going up to the air cleaner the leak goes unnoticed until it fills the air cleaner and the engine floods out. By that time the oil is severely diluted with gas. That is worst case scenario, lets hope it is one of the more minor problems.

[elmer]

Hello Rick,
this morning I checked if it smelled or, there was gasoline in the engine or in the air filter and in neither of them there was gasoline.
I have reviewed all the air and fuel pipes and I have not seen anything strange either.
How can I check them inside the tank? As you told me ,I have checked the metal line into the tank or a plugged filter sock in the tank but I dońt know how to do it
This morning when I started it, I immediately pumped gasoline from the gasoline pump.
I guess that's because I also launched it yesterday.
Thanks

[rickf]

Have you checked the fuel flow from the lines as I mentioned? That will give clues to the health of the filters and the pump valves and diaphragm. In order to check for leaks you will need to insert a short section of clear butyl hose that you can get at any hardware store. It will handle gasoline for a couple weeks but no longer. The idea is it put it inline somewhere convenient, preferably close to the fuel pump on the suction side, and see if there is and air coming through the line. If there is then there is a leak in the line somewhere. As far as the sock filter you can T in a vacuum pump into that same line I just mentioned and if you see any vacuum at all then it is getting clogged. anything over 5" of vacuum it is definitely time to replace it. Or, you could just put a new one on and know it is good. Do you still have the original factory filter at the carburetor inlet? When was the last time that was changed?

[elmer]

Hi Rickf,
I will test the flow that comes from the pump and the transparent tube in 15 days.I have M151 in other house where I usually live. I will inform you of how it will work.
About the filter that I use, I am sending you some photos where you can see the current one and another that I have new, Which one do you recommend I use?
I'm also sending you a photo that shows the fuel pump if you see something strange.

Thank you for your help

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IMG_8479.jpeg

[rickf]

Ok, Looking at the fuel pump the way the hoses are set up means the testing I was talking about using the clear hose and the vacuum gauge will be easy since you have a clamped on hose to the tank. No problems there. The pump looks pretty new? I see you have an inline filter which is good, (Ken will disagree, he hates inline filters. LOL) You also have to original filter already installed. The replacement you have will work but has very little capacity. Here is what I do on mine. Since I also use the inline filter, and use a quality one, I take the original filter off and I run a drill bit right through it and clean out all of the debris with a blow gun from both directions. Then I reinstall that filter back in place so it has the appearance of the original setup. The inline filter will protect the carb better than that little original one did anyway. I have rebuilt many 151 carbs that were loaded with crap that went right through the original filters and yet I have seen the inline filters clog so tight they stopped the engine for lack of fuel but the carb was perfectly clean. This way you only need to change the one inline filter from that point forward. And by the way, it is nice to see someone still running the proper fitting between the filter and the carb, even though the one you are running is actually the 90 degree fitting used on the A1. Those are extremely hard to find nowadays.

[elmer]

HI Rickf,
Here you can see in detail the piece rubber hose that I have inserted between the tank and the pump(in the metallic line).
Is that piece the one I have to replace with the transparent one, right? Does it always have to be full of fuel?
Thanks

IMG_8480.jpeg

[rickf]

That would be the one, keep that regular hose so you can put that back when done testing. That line should have no air in it at all when running and after shutting down it should not drain back to the tank for several days. the only way for it to drain back to the tank is a leaky suction side valve in the pump or air getting into the line below that valve. Now over a couple months it would be expected to drain back on a lot of vehicles and this would not be considered a problem. But when you crank the engine it should pull fuel from the tank instantly. 4-5 revolutions is enough to fill the line from the tank to the carb. When you put that clear line on that will drain that section of the line. I suggest you leave the switch off and watch that line as someone cranks the engine and note how many revolutions it takes for gas to come through the line. It should only be one or two revolutions to that point so close to the tank. I will add this, you already have the clear filter up by the carb so you can watch that for air bubbles also. Is that filter empty when you have the starting issue? Does it look like the entire line is draining from the carb all the way back to the tank?

[elmer]

The filter is empty when I don't start the vehicle in more than two weeks. I started it today, and when I stopped it, it was half full
I have looked several times if the carburetter or some tube loses gasoline but I have not seen any drops. The strange thing is that how the filter is placed, fuel should fall towards the carburetter, not towards the pump

[rickf]

It will only go to the carburetor if the float drops and calls for fuel. If the suction side valve is leaking on the fuel pump it will siphon the gas out of the line from the pump back to the gas tank. And just from the design of those filters they seldom ever fill completely due to the placement of the inlet and exit pipe inside the filter. The air is trapped in there while the fuel is already at the exit pipe. That is not a concern but the filter being completely empty tells you there is a downstream issue.

[elmer]

Hello, today I have checked all the tubes and none of them are leaking gasoline. I have also checked the screws, clamps, etc...
I have installed the transparent gasoline pipe between the tank and the pump and I have seen that in addition to gasoline, there are air bubbles. When I stopped the engine, the gasoline remains in that tube.
I have also put a transparent tube between the filter and the carburetor. There are almost no air bubbles. When I stopped the engine, that tube was emptied.
I also tested if the gasoline came out strongly and run vigorously. This morning before doing all this the engine started very well although it had not been started for 15 days.When the engine started, I immediately saw that the pump was sending gasoline to the carburetor
What do you think?
I would like add a video with air bubbles in the tube but I don't know what ext to use I've test .mov and .mp4 but it doesn't work

Elmer

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[rickf]

If you are getting air bubbles in the line from the tank then you have a leak in one of the lines. It could be the metal line inside the tank. One of our other members just had the same problem. The fact you are not seeing those bubble at the line by the carb is because the carb is not calling for much gas at idle and the fuel pump is probably breaking those big bobbles into tiny ones that are barely visible through that tubing. The fact that the upper tube drains back but the bottom does not just means it did not have time to fully drain the pump. If you go look now it is probably empty. It started quickly on the gas on the bowl of the carb, the fuel pump is pumping fuel well enough to catch up and fill the carb before it stalls. That is why you saw the bubbles in the lower line, it was moving a lot of gas at that point. I would guess that after that initial rush that slowed down. My take on this from what you have told me is that you have a slight leak in the suction line somewhere close to, or in the tank. You also may have a piece of dirt stuck in the inlet valve in the fuel pump. The pump sounds like it is pumping just fine other than that. Suggestions, take all those rubber hoses off the tank and make sure they are in good condition and then remove the suction tube from the tank and inspect it for rust or cracks where the tube meets the fitting. As far as the pump you can take both hoses off the pump and then get some carb cleaner and flush it through in the direction the fuel flows, tank to carb. This might push out whatever is in there. It is a long shot but the only other solution is to disassemble the pump and check the valves manually. I don't suggest this unless you are comfortable with this type of work. With the amount of flow you described coming from the pump I do not see why you would have an issue with very long cranking even if the line was completely empty. Starting one of these up from an empty gas tank situation generally only takes a half dozen turns of the engine before it fires. Be sure the filter sock in the tank is clean also when you check for leaks in that tube.

[elmer]

Thank you Rickf for,your master class
I will do everything yo say and I will explain my discoveries in the forum
Elmer