John Deere Z425 23 ohv b&s engine will not run under load or full throttle

john94 · May 6, 2018

I have a briggs and Stratton 23 ohv engine on a john deere zero turn 425 mower. It ran perfectly last week. went to start it this week to mow and now it sputters, black smoke and backfires all when trying to give it gas. it will not run fast nor can I engage the blades as the load makes it do the same thing and cut off. I changed the plugs, cleaned the carb, checked the valves, the blades move freely. It starts up and will idle and run on the lowest throttle setting but it will not do anything else. As soon as I try to push the throttle to fast and engage the blades it goes crazy. I don't know what else to try.

Richard001 · May 7, 2018

Welcome to TBN

Did you check the fuel pump?

What did the plugs look like? Can you post a photo of them?

Richard

RandyT · May 7, 2018

John I asked for model and type from the engine as well as any recent maintenance that had been do over at Lawnworld, but could you also post that here so in the end it may help somebody else.

BleedingOrange · May 7, 2018

If your engine is a twin, make sure both coils are firing, and you are getting a good spark at both plugs.
Sounds like it is only running on one cylinder.

john94 · May 7, 2018

The model number is 445577-0122-E1

john94 · May 7, 2018

Did notice that the o-ring seal for the intake manifold is cracked so I just picked up 2 to replace them both and see if that does the trick.

john94 · May 7, 2018

the fuel pump is fine the new plugs look good the smoke is just a little bit of black smoke not the white like with a blown head gasket

tomplum · May 8, 2018

In addition, is there a presents of gas in the engine oil? As stated, it could be running on 1 cylinder, though likely would be valve related. Things you want to know on this engine in the valve train. Valve covers off: Are all four rockers operating? The rocker studs tight? Are valve lifts similar? Is the lash set properly?

Richard001 · May 8, 2018

john94 said:
the fuel pump is fine the new plugs look good the smoke is just a little bit of black smoke not the white like with a blown head gasket

John, I wasn't talking about the new plugs. The old plugs will tell you what is going on in the engine.

See the chart below:

Richard

radios1 · May 13, 2018

check to see if the carburetor has a plastic needle valve.. if so, you need a rebuild kit with a stainless steel needle valve.. B&S sometimes skimps, but I think it's due to JD demanding it..(JD would get the repair)..