Need help with fuel pump issue

[dasto 0]

Magnum M12 starts on 312H by spraying starter fluid in carb then dies after fluid spent. Have verified: that fuel comes through fuel strainer; line from tank to fuel pump is clear; line from pump to carb is clear. Took off pump and it looks OK. Disconnect fuel line at carb then turn engine over and no fuel. Need advice.

[rmaynard 14,922]

Sound like either the diaphragm is ruptured, or one of the one-way valves is stuck.

[dasto 0]

Sound like either the diaphragm is ruptured, or one of the one-way valves is stuck.

Thanks. The diaphragm did not look ruptured. How do I go about unsticking the one-way valve you mentioned?

[dasto 0]

I took the pump apart again and the diaphragm is not ruptured. I blew on the inlet and the air didn't seem to go anywhere.

[dasto 0]

When I take the supply fuel line off the fuel pump (the one coming from the tank) should fuel come out of the hose? It doesn't, but maybe the line is similar height as tank and won't flow out just by gravity.

[rmaynard 14,922]

When working correctly, the one-way valves should allow you to blow into the inlet of the pump, but not the outlet. If the valves are stuck, you may be able to take them out and clean them, however, some pumps are more difficult to take apart than others. and you may not be able to do anything with them. A new replacement pump can be purchased at NAPA for around $60.00 or on eBay for less.

 

I believe the tank on your 312H sits lower than the pump, so suction is necessary to get the fuel moving. 

[dasto 0]

When working correctly, the one-way valves should allow you to blow into the inlet of the pump, but not the outlet. If the valves are stuck, you may be able to take them out and clean them, however, some pumps are more difficult to take apart than others. and you may not be able to do anything with them. A new replacement pump can be purchased at NAPA for around $60.00 or on eBay for less.

 

I believe the tank on your 312H sits lower than the pump, so suction is necessary to get the fuel moving.

Very kind of you to help. I put a short hose on the inlet of the pump so I could insert a compressed air trigger and test the valve. Air went into the inlet and out the valve with no problem. Now I'm wondering if I just have a weak fuel pump or diaphragm. It still isn't pulling fuel to the pump. But when I pull the line from the bottom of the tank at the shut off, fuel backs out of the line. So there is some fuel between the tank and the pump...either by gravity from the tank or from the pump trying to pull the fuel to the pump.

Seems like I am down to buying a pump?

[dasto 0]

Here is the latest. Before ordering a fuel pump I though it best to do one more experiment. Bought 6' of fuel line & attached to bottom of tank and inlet of pump. No change, still no fuel on exit side of pump. Then I removed pump from engine but kept the 6' of fuel line attached between the tank and the pump inlet side. Then I manual moved the pump arm & to my surprise just a couple of movements and it sprayed fuel across the shop. So, the pump is good but why don't it work installed in the engine? Would engine timing affect this?

[rmaynard 14,922]

Make sure that when the pump is installed the arm is on top of the cam shaft and not under it.

[dasto 0]

Make sure that when the pump is installed the arm is on top of the cam shaft and not under it.

Thanks. Yes, it is on top of the cam shaft. I place it carefully and it even squirts a little as I place it on top and then carefully tighten in place. However, then crank engine and not even a squirt comes out. It seems to be a mechanical issue. Before 100% tightened I can feel the arm on top of the cam and cause it to squirt. Once tightened flush, no more cam actuated pumping.

[dasto 0]

Here is some more info. I bought this unit new 25 years ago. The most recent 8 years only used to plow snow. The last 2 winters cranking did not provide fuel to carb. (I verified) So I started it with starting fluid & once started it pulled fuel and kept running. Now getting ready for winter and it won't continue running even with starting fluid assist. What do you think? Working the lever manually really shoots gas across the room, but nothing when installed and cranked.

[Geno 1,928]

I've seen this with weak pumps before.  Lets try this.  Put it all back together, take the hose loose only at the carb after the pump. Put a little air pressure in the tank and see if you can get some fuel to come out of the line where it is loose.  If you see fuel coming out of the line then stop and with the line still loose, crank the engine and see if it pumps. 

 

What you are doing is getting all of the air out of the system and priming the pump . 

[km3h 543]

It sounds to me like the cam shaft is worn. Fuel should shoot out of the pump just like it does if you actuate the arm by hand. You can go to NAPA and get a low pressure electric fuel pump and it will work great. This is not the first time I have seen this happen. Or you can tear down the engine and replace the cam shaft.

[Agage1 83]

I too like the electric pumps and they are about the same price as a new mechanical one. Every time I have a pump go down I usually don't mess with it and get a new electric one. The tractors start much faster too with an electric pump.

[dasto 0]

Still no go but some progress. Got it primed. Now have gas to hose that connects to carb. But no gas in carb bowl. Still starts with starting fluid and then dies. Took carb off and cleaned with carb cleaner. Still only starts with starting fluid & still no fuel in carb bowl but fuel still at carb entry and clear to float needle.

[Geno 1,928]

When you crank the engine after priming, with the hose off of the carb does a good amount of fuel come out of the hose at the carb?

Edited September 14, 2014 by Geno

[dasto 0]

When you crank the engine after priming, with the hose off of the carb does a good amount of fuel come out of the hose at the carb?

Sort of gently flows over the edges of the rubber hose. Doesn't shoot up in the air like a fountain.

[Geno 1,928]

Should be more than that.  Problem is likely the pump or lack of arm movement from something internal.

 

Do you have another tractor that you can switch the pump from?

Edited September 14, 2014 by Geno

[dasto 0]

Thanks everyone for the help. Time to retire for the night.

[MalMac 1,328]

If your line was dry from the tank to the pump, prime it again. You may need to fill the line up from the tank. Sometimes priming the pump won't work. The second they run through the prime and hit a empty fuel line they will not pump it from the tank. I have run into this several times. What I have done is take a oil can fill it with gas and insert it into the fuel line and fill it with gas. Connect it back to the pump. I don't know what it is about some of the newer pumps but like I said I have run into some of them that are not strong enough to pump gas through a totally empty line. Keep in mind though you might have a weak pump. If you go through all that and it still does not pump then you probably got a  bad pump.

[dasto 0]

Sort of gently flows over the edges of the rubber hose. Doesn't shoot up in the air like a fountain.

CORRECTION

I disconnected the hose at the carb and checked again. I cranked the engine for a while and observed the fuel flow. The cranking caused fuel to pulse out of the tube to a height of about 1/2". This is a regular pulse and liquid rise. Does this sound normal.

There is still no fuel in the carb bowl. What could be preventing this?

If your line was dry from the tank to the pump, prime it again. You may need to fill the line up from the tank. Sometimes priming the pump won't work. The second they run through the prime and hit a empty fuel line they will not pump it from the tank. I have run into this several times. What I have done is take a oil can fill it with gas and insert it into the fuel line and fill it with gas. Connect it back to the pump. I don't know what it is about some of the newer pumps but like I said I have run into some of them that are not strong enough to pump gas through a totally empty line. Keep in mind though you might have a weak pump. If you go through all that and it still does not pump then you probably got a  bad pump.

Thanks for your help. I now have a good prime. But it still just runs through the starting fluid. I get no fuel in the carb bowl. See above post.

[rmaynard 14,922]

If I am understanding you properly, you are saying that when the hose from the pump outlet to the carburetor inlet is disconnected, you get a steady pulse of fuel when turning over the engine, yet there is no fuel in the carburetor bowl when you remove it? That sounds to me like the float valve in your carburetor is stuck closed.

[dasto 0]

If I am understanding you properly, you are saying that when the hose from the pump outlet to the carburetor inlet is disconnected, you get a steady pulse of fuel when turning over the engine, yet there is no fuel in the carburetor bowl when you remove it? That sounds to me like the float valve in your carburetor is stuck closed.

Correct summary. I took the carb off last night and used some carb cleaner on it. Is there anything else I can do?

[dasto 0]

If I am understanding you properly, you are saying that when the hose from the pump outlet to the carburetor inlet is disconnected, you get a steady pulse of fuel when turning over the engine, yet there is no fuel in the carburetor bowl when you remove it? That sounds to me like the float valve in your carburetor is stuck closed.

My float valve does not have a spring around it. Is that normal?  It is a small piece that is shaped like a pyramid on one end, kind of reddish and square metal on the other end, butts against the back plate of the float and seals and unseals.

[rmaynard 14,922]

No spring on it. It floats freely on top of the float tab. Best to completely remove the float and valve to clean it. When assembled, and holding the carburetor in a normal mounting position, you should be able to raise the float up, and then let it hang, and the little brass needle should drop immediately with it. If it hangs up at all, get a carburetor kit and replace it.