Diagnose a Briggs

[Prospecter]

I have a JD Zero Turn (the cheap one) with a rebranded Briggs engine that I cannot keep running. Obviously some sort of a fuel issue. I never use untreated fuel, have repeatedly changed fuel filters. After fighting this all summer, I changed plugs and fuel. Still no luck. Dealer dismantled and cleaned the carb, changed the starting solenoid, fuel filter, drained the fuel, and changed the tank cap.

The engine starts, and sometimes will run fully choked. I am at a loss. Anyone have an idea?

 

[Bessy]

When you say it runs sometimes when choked, that means it's likely not getting enough fuel when the choke is off. I would be inclined to change out the carb entirely and see if that fixes the issue. Buy an aftermarket bolt on replacement carburetor, and flush the fuel line from the tank to ensure there's no debris in the fuel lines restricting fuel flow.

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[Jlbc212]

Remove the flywheel and check to see if the key that aligns the flywheel with the crankshaft is sheared or partially sheared. A sheared key will throw the timing off. If the engine does start, as with your mower, it will not run well.

 

[laser3kw]

Remove the flywheel and check to see if the key that aligns the flywheel with the crankshaft is sheared or partially sheared. A sheared key will throw the timing off. If the engine does start, as with your mower, it will not run well.

and.. along with that.... check the valve lash / rocker arms. They have ben known to slip and cause **** and blow problems.

 

[rustyjames]

I've seen exhaust valves warp when the engine heats up, that'll cause this.

 

[freudianfloyd]

I would check the fuel lines for cracks before doing anything else.

 

[lostmind]

Start with a compression test , if good then go to fuel circuit.
Try spraying carb cleaner in the inlet to see if it will continue running.

 

[Rabbit929]

I would check the fuel lines for cracks before doing anything else.

I second this.
The ethanol in the fuel (even if you use premium at a blend pump) dry rots your fuel lines.
Cheap reassurance. The inside of the hose will collapse under suction, starving the fuel.

Screw checking the valves, compression, etc. at this point. Fuel lines, carb, fuel pump if it has one, (which my 20hp vanguard had a small vacuum pump for the fuel, looks like an in-line black disk and was known for issues)

If it surges a lot then dies there’s an air screw on the carb you can pull out and clean.
Order of diagnostic for you should go fuel line, carb, then compression, and so on. Most likely the carb or fuel line.

 

[CraigStu]

Before taking the carb apart I'd order a few gaskets. Mainly the float bowl gasket and whatever seals the brass piece into the bottom of the float bowl. These quite often disintegrate when removed and then you are done. Get a can of carb cleaner and be sure it has the little red plastic tube. Blow out every passage and crevice you see and re-assemble.

 

[freudianfloyd]

I second this.
The ethanol in the fuel (even if you use premium at a blend pump) dry rots your fuel lines.
Cheap reassurance. The inside of the hose will collapse under suction, starving the fuel.

Screw checking the valves, compression, etc. at this point. Fuel lines, carb, fuel pump if it has one, (which my 20hp vanguard had a small vacuum pump for the fuel, looks like an in-line black disk and was known for issues)

If it surges a lot then dies there’s an air screw on the carb you can pull out and clean.
Order of diagnostic for you should go fuel line, carb, then compression, and so on. Most likely the carb or fuel line.

The other issue with bad fuel lines is if there is a crack, or even a pin hole, it prevents the carb from drawing fuel out of the tank. Just like if you try to drink from a straw with a hole in the side.

 

[Prospecter]

Thank you all! GJ comes through again! All good ideas that hold a lot of promise.

 

[Hot shot]

Compression
Fuel
Spark
Yal have covered it all

 

[man of steel]

Try take the fuel tank cap off and then start. I was chasing the same thing on a Craftsman Lawn tractor for a while until I figured it out. Vents in the cap now have valves to keep fumes out of the atmosphere and these are known to cause problems.

 

[VC-Racing]

Tank vent .

 

[theoldwizard1]

When you say it runs sometimes when choked, that means it's likely not getting enough fuel when the choke is off. I would be inclined to change out the carb entirely and see if that fixes the issue. Buy an aftermarket bolt on replacement carburetor, and flush the fuel line from the tank to ensure there's no debris in the fuel lines restricting fuel flow.

Specifically the primary/idle circuit is clogged or partially. A heated ultrasonic cleaner might get the clog, but no guarantee. Locating the primary circuit and "reaming it out" with a fine wire might get it. The problem is LOCATING the primary circuit. It might only be accessible behind a Welch plug. Probably cheaper to buy a Chinese replacement.


Segue - All gasoline carburetors have at least 2 fuel circuits; primary/idle and main/high speed. Fancy carbs (Holley) may have more, but on small engines there is typically 2. Calling the first one a "idle" circuit can confuse some people. Yes, it is the only circuit use when idling, BUT it should be called the "primary" because it responsible for delivering a certain amount of fuel ALL OF THE TIME !

 

[DFB]

We had a DR mower at the orchard that the guys would take in the field to cut around the trees. Kept quitting while they were mowing. It would restart every time, but wouldn't stay running and it was serviced multiple times by the local equipment dealer that sold it but the problem still persisted.

Finally I got a chance to look at it turned out the fuel line had been ******* close to motor with zip tie , was collapsing on itself after it got hot and was restricting the fuel flow . I rerouted slightly away from the engine abit and less of a sharp angle. Havent had a problem since. Personally I really don't think was the original config and maybe someone did that even the at dealership.

My biggest clue was watching a couple workers together limp it back to the barn

As long as one guy kept jiggling on the fuel line while the other guy ran the handlebar and controls it made it all the way up the hill back to the barn.

Somethin easy to look for...a hose with a tight bend can fold over enough when hot to cut off the fuel