Can a mechanical fuel pump just "die" without warning?

[Duff 206]

Hi, folks,

I was mowing with my 312-8 tonight - ran fine, uphill, downhill, varying loads - no problem. This tractor has been running like a Swiss watch ever since I got it four years ago. As good fortune would have it, I had just finished mowing and pulled the tractor up next to the hose bib on my house to rinse it off and wash the underside of the deck. I left it running and ran inside to be sure the wife had finished taking her shower (94 degrees here today and she had been up at the farm talking care of some four-legged horses) before I turned on the hose when I heard the engine start to die out, come back, then die completely. I tried starting it; it would run for a few seconds on full choke then die out - fuel starvation.

So following the good advice I've seen here over the years, I started troubleshooting:

1) Loosened up the fuel fill cap and turned the engine over with it loose - nothing, so no vapor lock at the tank.

2) Pulled the air cleaner then took off the fuel line on the output side of the pump. Turned it over - nothing.

3) Pulled the fuel line where it comes out of the gas tank and turned the petcock back on - good flow out of the tank, so the filter screen wasn't clogged.

4) Blew air (lung-power, not a high pressure air line) through the fuel line from the tank end - all kinds of gas spewed out at the output side of the fuel pump!

From this I am guessing my fuel pump just bought the farm. So is this a common way for a pump to quit? For some reason I thought they would show signs of weaking before quitting completely, but that may just be my feeble (misguided?) memory at work.

The engine is a Magnum 12 with about a thousand hours on it; well maintained by the previous (and only) owner before me.

Advice and observations welcomed!

Duff :thumbs:

[BOWTIE 226]

HELLO DUFF, TAKE THE PUMP OFF AND HOOK A HOSE TO THE INLET AND PUMP IT BY HAND.PUT THE HOSE IN GAS,KERO OR WATER FOR THE TEST. I WOULD ALSO CHECK THE OIL FOR GASOLINE IT MAY HAVE LEAKED PASS THE THE DIAPHRAM. GOOD LUCK

BOWTIE IN OHIO

[rmaynard 16,343]

The diaphragm on the inside of the pump may have developed a hole. Also, there are two small check valves inside the pump. One may be stuck. In any case, I would remove the pump, take the four screws out that hold the two halves together, and take a look. I don't know if the Magnum pump has a rebuild kit available (doubt it), but maybe you will be lucky and find some debris causing one of the check valves to remain open.

Also, I have been told that the ethanol in gasoline will deteriorate the diaphragm much quicker than just gasoline. The new replacement pumps are being made with diaphragms and internal parts that are impervious to ethanol. A new pump for that model can be had for a little as $30.00 plus shipping.

[Duff 206]

The diaphragm on the inside of the pump may have developed a hole. Also, there are two small check valves inside the pump. One may be stuck. In any case, I would remove the pump, take the four screws out that hold the two halves together, and take a look. I don't know if the Magnum pump has a rebuild kit available (doubt it), but maybe you will be lucky and find some debris causing one of the check valves to remain open.

Also, I have been told that the ethanol in gasoline will deteriorate the diaphragm much quicker than just gasoline. The new replacement pumps are being made with diaphragms and internal parts that are impervious to ethanol. A new pump for that model can be had for a little as $30.00 plus shipping.

Good info, Bob - thanks!

Since we're into the summer season and I've got more irons in the fire than a blacksmith at a rodeo, I broke down and ordered a new one. This machine is 23 years old and I am indeed stuck running fuel with ethanol, although I keep threatening to go to the local airport and stock up on some LL100 Avgas. This winter I'll disassemble the old pump and if it's repairable I'll put it on the shelf as an emergency spare since I have three more Magnum engines.

Since I'm not a purist, I may eventually switch them all over to electric fuel pumps and be done with it. Time will tell.....

Thanks again!

~Duff :thumbs:

[smoreau 658]

I know what you mean by to much to do this year! Check out this web site and it will tell you if your near one of these stations that sell pure gas with no ethanol in it!

http://pure-gas.org/