Briggs 44M777 Surging issues - Need help!

[Airbender]

In 2023 I bought a used 2009 Craftsman PYT9000 that has a B&S 24 hp 44M777 TYPE 0790 B1 CODE 091219YG. Ran great for 1.5 years. A few weeks ago, I started getting surging issues. From a cold start, it will run fine for about 20 minutes, then starts surging so bad that it shuts down. I have so far replaced the carb, vacuum hoses, all intake gaskets, plugs, fuel pump, air-filter, and OEM B&S intake manifold. I have checked the governor linkage & attachments - everything is tight and the springs are in place. This thing is STILL surging 20 minutes after cold start. Any suggestions are VERY much appreciated!

 

[oldnslo]

Have you checked compression when cold and when hot?

Also check for spark when hot.

 

[Tinhack]

Surging is always fuel related--Too much or too little. The carb is always a suspect with clogged jets or the wrong jets. A sinking float or trash under the float valve. Fuel filter clogged. Choke not releasing or opening all the way. These are all causes of hunting or surging. Have you flushed the tank? Replaced the fuel filter?

Remove the fuel bowl and see if there's debris in the bottom. If there is, you need to do some cleaning. You probably do-do'ed your new carb as well. It will need disassembly and cleaning.

 

[SPYDERLK]

In 2023 I bought a used 2009 Craftsman PYT9000 that has a B&S 24 hp 44M777 TYPE 0790 B1 CODE 091219YG. Ran great for 1.5 years. A few weeks ago, I started getting surging issues. From a cold start, it will run fine for about 20 minutes, then starts surging so bad that it shuts down. I have so far replaced the carb, vacuum hoses, all intake gaskets, plugs, fuel pump, air-filter, and OEM B&S intake manifold. I have checked the governor linkage & attachments - everything is tight and the springs are in place. This thing is STILL surging 20 minutes after cold start. Any suggestions are VERY much appreciated!

Are you aware of the "valve guide migration" problem that many B&S engines have shown? Essentially the guides - usually exhaust - move toward the rocker arms, eventually interfering with the ability to fully open the valve. Many clever fixes have been devised posted online. But you will have to diagnose it first to assure that is the underlying issue in your case. If so, and left alone, it will finally bend pushrods and wear out the camshaft.

 

[tomplum]

It is worth running it with a hunk of 1/4 " fuel line from the filter dropped into a fuel can to confirm there isn't a delivery issue with the tank etc.

 

[DJ54]

Could also be the fuel cap not venting. A common issue after 20 or so minutes of run time. Loosen the fuel cap enough it's fairly loose and run it and see what happens.

 

[Tinhack]

Are you aware of the "valve guide migration" problem that many B&S engines have shown? Essentially the guides - usually exhaust - move toward the rocker arms, eventually interfering with the ability to fully open the valve. Many clever fixes have been devised posted online. But you will have to diagnose it first to assure that is the underlying issue in your case. If so, and left alone, it will finally bend pushrods and wear out the camshaft.

Yes, but that can happen with any air cooled engine with valve guides. And that issue doesn't fix itself when the engine cools down to run another 20 minutes. It also causes a flat-out miss or no-start condition not a surging problem.

 

[stevem5215]

Had the same problem on my 24hp Black Craftsman. Bought some Mechanic in a bottle at Lowe's. Ran it for an hour and surging was gone.

 

[Fuddyduddy1952]

One mower here did that. A leaf was in gas tank. As mentioned, check/clean tank.

 

[DJ54]

Could also be the discharge nozzle/emulsion tube cross drilled holes partially plugged. That will need to be removed to clean.