Magnum M12 - only runs for a few seconds.

[TC10284 111]

I have a Magnum M12 on a 312-8. I don't have the tractor model or serial because it has faded out to white. 

 

The starter mount broke on it with the previous owner. I had that rewelded by a professional welder. 

 

I remounted the engine, connected the wires, cables, etc. 

 

Fast forward some. I can get the engine to run only for a few seconds. I tried taking apart the carb and blowing out the jets. Reinstalled, same deal.

 

Tried another walbro carb of same model. Same deal. It only runs for a few seconds. 

 

Previous owner replaced the fuel pump on it and didn't turn the inlet or outlet angles properly, but I can see where it is pumping fuel. Not very strong, but it comes out of the hose and overflows. 

 

Both carbs have fuel in the bowl after the bowl was emptied. So I know fuel gets to the bowl. 

 

Also tried a new H10c plug. 

Edited May 5, 2021 by TC10284

[ranger 1,750]

Is the low oil level switch ok? Connections to it ok? I can’t remember if low oil causes the engine to stop, or prevents you from starting. Perhaps vibration from engine running is causing a connection issue somewhere in the ignition circuit if you are sure fuel is getting through? Does the engine fire up straight away after stopping, or do you have to crank it for a few seconds?

 

Doug.

[TC10284 111]

3 minutes ago, ranger said:

Is the low oil level switch ok? Connections to it ok? I can’t remember if low oil causes the engine to stop, or prevents you from starting. Perhaps vibration from engine running is causing a connection issue somewhere in the ignition circuit if you are sure fuel is getting through? Does the engine fire up straight away after stopping, or do you have to crank it for a few seconds?

 

Doug.

 

The low oil level switch is the silver looking box sitting close to the two fuses, if I'm not mistaken, correct? Oil level looked alright but could use a little more to be sure. I'll check connections there too. 

 

I actually have to dump fuel into the carb to get it to run. That and the angles of the inlet and outlet on the fuel pump makes me think I need a new fuel pump. 

[Ed Kennell 38,227]

Definately sounds like you have a fuel delivery problem.

Pull the fuel line off at the carb and hold it in a container while a helper cranks the engine.

You should see a good spurting of fuel.

If you don,t see a good supply to the carb,  pull the linlet line to the fuel pump. you should see a free flow of fuel.  If you do, the pump is bad.

Loosen the fuel tank cap...could be a blocked vent hole.

Edited May 5, 2021 by Ed Kennell

[ranger 1,750]

1 minute ago, TC10284 said:

 

The low oil level switch is the silver looking box sitting close to the two fuses, if I'm not mistaken, correct? Oil level looked alright but could use a little more to be sure. I'll check connections there too. 

 

I actually have to dump fuel into the carb to get it to run. That and the angles of the inlet and outlet on the fuel pump makes me think I need a new fuel pump. 

If you’re dumping fuel into the carb to get it to start, it sounds as though the fuel pump is suspect. Try connecting a length of fuel line to the carb and to a temporary tank (gravity feed), above the engine, and see if it keeps running. If it does you know the pump has an issue.

Doug.

[8ntruck 7,016]

Is there a screen inside the gas tank on the fuel hose fitting?  That might be clogged.

[TC10284 111]

I'll try a temp fuel tank and also a new fuel pump. 

 

I checked for fuel flow from the tank. I pulled the line off and then opened the shut off valve and got good flow from the tank. 

[oliver2-44 9,760]

Since that tractor has the tank under the seat you might switch to an electric fuel pump. Many of us have had good luck with the Facet electric pump. 

[DennisThornton 4,769]

Fuel delivery is not keeping up with fuel use.  Fuel flow issue somewhere.

[TC10284 111]

22 minutes ago, DennisThornton said:

Fuel delivery is not keeping up with fuel use.  Fuel flow issue somewhere. 

That's what I'm thinking. Hopefully a new fuel pump resolves. 

 

The confusing part is that the bowl appears full on both carbs when I remove the bolt to check it. 

 

We'll see. 

[DennisThornton 4,769]

8 minutes ago, TC10284 said:

That's what I'm thinking. Hopefully a new fuel pump resolves. 

 

The confusing part is that the bowl appears full on both carbs when I remove the bolt to check it. 

 

We'll see. 

Slow flow could fill the bowl but not keep up while running.  Blockage somewhere.  It's happened to me several times.  Fuel shut-off, debris anywhere it can collect, pinched fuel line, filter, bad mechanical or other fuel pump.  Something simple hiding somewhere.

[tunahead72 2,424]

I wonder if the carb inlet needle(s) might also be sticking closed once the bowl is filled.  You mentioned you took the one carb apart and blew it out, but have you thoroughly soaked and cleaned the carbs you've tried?

[Ed Kennell 38,227]

13 hours ago, Ed Kennell said:

Definately sounds like you have a fuel delivery problem.

Pull the fuel line off at the carb and hold it in a container while a helper cranks the engine.

You should see a good spurting of fuel

Did you check this?

[TC10284 111]

A new fuel pump resolved the issue, and after priming the pump.