21HP B&S John Deere LA120

[kcareabroker]

Hello,

I have an about 15 year old John Deere LA 120 that has up to this point been a good running lawn mower with some typical maintenance done. So for that I am happy. Starting last fall through about a month ago, the engine began acting like it wanted to die while mowing. I could use the choke to keep it running and eventually it would come out of it and run normal. This usually is after it is started and ran for a few minutes until it was running for about 15 minutes. It was easy to start and occasionally would do it after the mower was running for awhile. The last time I ran the mower it acted like it was running on one cylinder with limited power and an obvious miss.

What i have done so far:
replaced spark plugs
replaced carb with a new one
replaced fuel pump
repaired small hole on the vacuum tube that goes from the valve cover to the fuel pump. I plan to purchase a new one but I know this one isn't leaking at the moment.

The engine seems like it isn't getting gas. With the air filter out, I can spray some start fluid in the inlet for the carb and it starts and idles fine until the spray is consumed. The carb fuel bowl is full of gas. I have pulled the fuel line off and while turning over the motor, gas does spurt out of the fuel line. Gas will also trickle from the inlet of the carb if I pull the fuel line off.

The engine is getting spark to both cylinders. I have pulled both spark plugs and left the wires on having them fairly close to the motor while cranking over and both deliver a decent spark.

Not sure where the heck to go from here. Not ready to give up but running out of ideas since the motor seems to be getting, air, fuel, and spark. Any ideas?

The motor model number is 441677.

 

[bertsmobile1]

After 15 years there will be a stack of debris in your fuel tank.
When grass clippings get in there the petrol replaces the water in the clippings so they are almost the same density so the fuel so they float till you start to draw fuel when they get sucked into the fuel outlet and partially block it.
The vent in the fuel cap also clos up creating a partial vacuum in the tank preventing full fuel flow
The fuel lines get attacked by the addatives in modern fuel and degrade blocking off the fuel supply.

 

[slomo]

After 15 years, that engine needs a full service. Things like:

1.Remove top engine/flywheel shroud/cover and clean the cylinder block cooling fins of grass, oil, dirt and bugs. Make sure the bottom of the cylinder/s is clean and free for air movement.
2.Dump fuel tank and clean out with pure ammonia. Shake it around real good. Dump that out and refill with ammonia. If it needs it let it soak.
3.Install new fuel lines and filter
4.Valve clearance adjustment
5.Run fuel stabilizer year round

Was this a new OEM Briggs carb or a Chinese carb? Definitely sounds like a carb issue.

slomo

 

[kcareabroker]

After 15 years, that engine needs a full service. Things like:

1.Remove top engine/flywheel shroud/cover and clean the cylinder block cooling fins of grass, oil, dirt and bugs. Make sure the bottom of the cylinder/s is clean and free for air movement.
2.Dump fuel tank and clean out with pure ammonia. Shake it around real good. Dump that out and refill with ammonia. If it needs it let it soak.
3.Install new fuel lines and filter
4.Valve clearance adjustment
5.Run fuel stabilizer year round

Was this a new OEM Briggs carb or a Chinese carb? Definitely sounds like a carb issue.

slomo

Yup. Off Amazon. Bad thing is its doing what it was prior to replacing the carb. No sputter, pop, or any signs of life unless I shoot some starter fluid in.

 

[slomo]

Yup. Off Amazon. Bad thing is its doing what it was prior to replacing the carb. No sputter, pop, or any signs of life unless I shoot some starter fluid in.

Was it an OEM Briggs or Chinese?

slomo

 

[tom3]

Any chance of some water in the gas? Just a little in the bottom of the carb bowl and the engine won't run right, or at all.

 

[kcareabroker]

Was it an OEM Briggs or Chinese?

slomo

Chinese. Was like 23.00 shipped.

 

[kcareabroker]

Any chance of some water in the gas? Just a little in the bottom of the carb bowl and the engine won't run right, or at all.

Its possible but not likely. It is newer gas in the mower. I may try to put the fuel line in a gas can with new gas just in case as well as I am going to manually provide vacuum to the fuel pump to be sure its not that but it seems like the carb is getting gas. Grrrrr. Frustrating. lol.

 

[kcareabroker]

Just received another carb and hope to put it on very soon. Since I have to take the intake off to change out the carb is there anything I should be checking out while that portion of the motor is apart? I have to assume the valves are functioning since I can spray starter fluid into the intake and the motor runs and sounds good until the spray runs out.

 

[kcareabroker]

Just to follow up. The fellas rust suggested bad gas, you were spot on. Never in a million years would I have thought that and didn't. It finally came down to that after replacing all the stuff I did. Lesson learned. I disconnect the gas hose to my filter and to the carb and drained as much as I could out. Put the end from the filter into a small gas can with fresh gas, reconnect the carb, cranked it for a bit and it fired right up and idled perfect. Problem solved! Now to drain the tank and replace with fresh fuel.

Thanks again for the suggestions. I Should have listened more!