How do I correct engine surging?

[kc5dlo]

The old 18hp opposed cylinder engines I had were real susceptible to having a surging condition when the air filter was dirty.

 

[silvertramp]

Seafoam is not snake oil, that is unless snake oil is good for cleaning carbs and making intake valves clean as a whistle. I have used it for years, every time I have a engine that has set too long and doesn't want to run right, it has worked. Snake Oil, LOL!

Seafoam sure helped my cranky 4 carb 79 Goldwing. I use it as a stabilizer for my bikes and small engines when putting them to bed for the winter.

 

[pmsmechanic]

I agree there is nothing "snake oil" about sea foam. It works! That being said your idle circuit is plugged in the carb. The surging is from the engine not being able to run on the idle circuit.When the revs slow down the governor opens up the throttle and the engine pulls gas out of the main gas circuit. The engine speeds up too much and the governor slows it down and since the idle circuit is plugged the governor opens up the throttle again. And the cycle just keeps repeating.

If you are lucky enough to own an older mower with an adjustable idle jet screw you can often get away with just gently turning the screw in while counting the turns in and the turning the screw back out the same amount. Do not confuse the idle jet screw with screw that adjusts the idle speed. The idle speed screw is closer to the top of the carburetor and adjust either with or against a part that moves. The idle jet screw if it exists will be lower and turn into the carburetor body.

If you have a newer engine with a set idle screw then you need to take the carb apart and clean it. I or someone else can walk you through that but lets try the simple stuff first.

I'm just going to add that spraying Sea Foam down the carb with the engine running might do the trick too. Yamaha also sells a Combustion Chamber Cleaner that will make dull carb parts look like new again. It's also designed to spray into a running engine. I've never used it in that way but you soak ugly looking carb parts in it and they come out looking like new.

 

[Deere Dude]

Begin with the easy stuff first.
I would dump the old gas and start over with non-ethanol gas and put the right amount of Sea Foam in. If it ran all right last year, it points to fuel. If that doesn't clean it up, check the other more difficult stuff.

 

[DJ54]

My 1965 vintage 8 hp Wheel Horse had a surging problem several years ago. Come to find out, the two tiny bottom cross drilled holes in the discharge nozzle were plugged, and was the problem. Cleaned them with a wire plucked from a wire brush. A spritz of carb cleaner, and blew out with compressed air fixed the problem.

Had the same problem with my newer '88 model, 10 hp. This had to do with the main jet. Seems crud had built up on the tip, restricting fuel. A small spot on a shop rag soaked with carb cleaner took it right off. Also cleaned the seat. Both run like a champ now.

And I too use Seafoam, more of a preventative now. Add it 3-4 times over the summer to keep the system clean.

 

[Hoff64]

I know this thread is old, but the surging issue is new to me. My wrinkle is that after my John Deere LA 135 (B&S engine) surges under the load of the engaged blades for 30 to 45 minutes, it then purrs like it was brand new and no longer surges. What would explain the "shift" after 30 to 45 minutes? And does cutting my grass for 30 to 45 minutes while the engine surges cause any damage to my engine?
Thanks for any input!

 

[Hoff64]

And to clarify, I changed my fuel, my fuel pump, my fuel filter, my spark plugs, my fuel tank cap, and added Sea Foam to my fuel... yet the surging continued until the 30 to 45 minutes passed.

 

[oldballs]

I've studied this phenomenon with my gas engine L& G tractor. I never did get it solved. My last gasp is to take the carb off and do a rebuild. In your case there may be an air leak e.g. in the intake manifold that causes surging when cold, but closes up when the engine get hot. .... just a guess. Good Luck,
Mike

 

[pmsmechanic]

I've studied this phenomenon with my gas engine L& G tractor. I never did get it solved. My last gasp is to take the carb off and do a rebuild. In your case there may be an air leak e.g. in the intake manifold that causes surging when cold, but closes up when the engine get hot. .... just a guess. Good Luck,
Mike

Or there could be a small piece grass stuck in one of the jets. Just enough to make it run lean.

 

[radios1]

I know this thread is old, but the surging issue is new to me. My wrinkle is that after my John Deere LA 135 (B&S engine) surges under the load of the engaged blades for 30 to 45 minutes, it then purrs like it was brand new and no longer surges. What would explain the "shift" after 30 to 45 minutes? And does cutting my grass for 30 to 45 minutes while the engine surges cause any damage to my engine?
Thanks for any input!

I have the LA145 and they used a PLASTIC needle valve in the carburetor instead of stainless steel!.. replacing that with the stainless steel needle valve solved many problems!. too much or too little fuel will cause surging.. if it's not getting enough fuel, you can close the choke a bit to stop the surging. if it's getting too much fuel, check that the choke is fully open when it should be..