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Only runs with choke on.Clean tank new lines,and filter.cleaned float bowl,carb appears to be new.

MTD Yard machine Model 13AO772H755, Briggs 15.5 42 inch deck

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Tracking down fuel problems.

NOTE:The MTD Yard machine Model 13AO772H755, Briggs 15.5 hp engine does not have a fuel pump.Ignore all references to the fuel pump.However the rest of the fuel pathway should be checked just the same.Watch the video.

  1. Make sure there is plenty of fresh fuel in tank. High Octane less than one month old. Water in the fuel system will often cause hard starting, low power, backfiring, surging or stalling
  2. Is there a cut off valve at the gas tank? If so check that it is open or working if it is electric.
  3. This step comes from repeated personal experience with JD gas tanks. Remove fuel line from filter and remove the filter, gas should pour out of the hose coming from the tank. (look at the filter before removing it, it should look at least 1/2 full of fuel.) If gas does not pour out remove gas tank cap. If fuel flows now, you need to unclog the cap vent or replace the cap. The vent is that tinnnny little hole in the center of the cap. If the fuel still does not flow then blow air from the filter end of the hose back up through fuel line to blow out any blockage inside the gas tank.
  4. Consider my own experience when my engine to quit in the middle of a mowing job: I was mowing along on my LA145 (200 hours on it) when it slowed down and died. Before it died, it acted like it was losing power. It thought it was only firing on one cylinder. I waited about 20 minutes and it restarted after a lot of cranking and some priming. I made a couple more mowing passes; the same thing happened again.

    I knew this mower was in top running condition. There were no engine misses, no backfires. It was not abnormally hard to start. The carburetor was clean, the coils were good, the plugs and fuel filter were recently changed. Lifting the hood, I noticed the fuel filter was nearly empty. It should be ½ full, or more. I pulled the hose off the tank side of the fuel pump and saw there was no fuel flow.

    Gas should gravity flow from the tank to the fuel pump, if the tank has a good supply of fuel. I wiped the hose off and blew air back into the fuel tank. It helps to take the gas tank lid off first. After I got a good flow of air going back into the tank (you can hear the bubbles) the fuel began to gravity flow back through the hose at a decent clip. This fixed the problem. There is likely silt build up in the tank and it settles at the output port blocking the flow of fuel.

    The problem repeated itself several times last summer. Back at the shop, I used compressed air (turned down to 20 psi) to blow the line clear. The problem reoccurred this spring. I used the same method to clear the line.
  5. Do your self a favor, leave the gas cap off and turn the outlet air on your compressor down below 20 psi. If the tank is nearly full you will blow gas out of the tank. Do this outside if possible; at the very least you need a well ventilated area. After blowing air from the air filter back to the tank, you may have to reverse the process and pressurize the tank to get the fuel started. I place my hand over the open tank and hold the air hose between the joint of my thumb and forefinger to seal the tank, and then squeeze the trigger. Once you have a good fuel flow out the line to the filter, put on a FRESH FILTER. Try cranking the engine. If it still does not start move on to the fuel pump and carburetor
  6. Check the fuel pump. The fuel pump system on the twin Koehler and the Twin Briggs (and others) are almost identical. Watch this excellent, eight minute, video to learn how to check the fuel system, including the pump, up to the carburetor. . Small Engine Repair Checking Vacuum Fuel Pump Fuel System on Kohler Twin...
  7. Note: My engine was starting hard and dying in the field this year (March 2015). While doing a valve adjustment, I found a hairline crack in the bend of the vacuum hose powering the fuel pump. It's the short hose running from the valve cover to the fuel pump. The fuel pump will not work if this hose is cracked.
  8. Many systems have a fuel shut off solenoid. This is a small cylinder on the bottom of the carburetor. It has two wires running to it. It should make an audible click when you turn the key on. If it does not click you will have to replace it or track down an electrical problem.
  9. If this has not solved the problem you may have to remove and disassemble, clean, or rebuild the carburetor at this point. You may have water, dried fuel (varnish) or trash in the carburetor bowl. Before removing and disassembling the carburetor try draining the bowl. Or, take the bowl off, careful not to drop the small parts inside. Clean the bowl and replace. I often remove the bowl on small engines and save the hassle of a complete carb removal.

NOTE: Connect a volt meter across the two battery posts. If battery voltage drops below 9 volts when cranking or while the engine is running, the fuel cut off solenoid will not function. That means the engine will not start or will die soon after starting. So check your battery voltage before, during, and after cranking. If the battery voltage is good before but drops below 9 volts while cranking this is generally a sign the battery has one or more bad cells. Replace the battery. If the battery is in fact good, and the voltage is still dropping, you may have a bad starter motor which is drawing too much amperage.

If you find this fuel checkup does not solve the problem, repost your question with updated info and I will walk you through the next step. Tracking down a spark problem; yes, your problem could involve the coil or any part of the ignition/spark system. (Not as likely as fuel)
Small Engine Repair Checking Vacuum Fuel Pump Fuel System on Kohler Twin...

Posted on Apr 15, 2015


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