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I have a John Deere mower with a liquid cooled Kawasaki engine which has approx 500 hr. When throttle in fast idle position, the engine surges badly. Replaced fuel hoses, fuel filter, took carb off and cleaned. No vacuum leaks detected. The engine will smooth out and run normally when the mower deck is engaged, and mows normally. This only occurs under no load or if traveling without deck engaged. All of the adjustments to the carb linkage and governor linkage was adjusted per the repair manual. Also the surging will stop under no load if the choke is just partially engaged. Any ideas would be appreciated. Duane

dgrif said:

the surging will stop under no load if the choke is just partially engaged.

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I think that's a telling clue right there. I've heard of this symptom where the carburetor's main jet and/or nozzle is clogged or obstructed with old slimy fuel. With the throttle in FAST and the choke OFF, the engine is running lean (too much air vs. too little fuel) due to the obstruction, and surges/stalls. When you move the choke to ON, the engine gets less air, and the ratio of air-to-fuel is now okay, and then engine runs smoothly. At least that's how an engineer explained it to me :biggrin:

You may want to double-check the carb and be absolutely sure the main jet/nozzle are pulled out and cleaned very thoroughly. Use compressed air and aerosol carb cleaner. Even a tiny, tiny bit of debris or slime can cause the surge problem.

In a really bad case, you may need to simply replace the carb. Depending on the engine, this can be faster/cheaper than trying to sort-out a rebuild or overhaul kit on one, and you can be sure it's clean on the inside. So, you may want to price what a new carb would cost, and see if it's a more (overall) economic solution.

I spend over an hour and a half trying to clean and rebuild a small mower carb and get it running on my mower, and never could get it right. Ended up buying a new one for less than $25 and it worked great.

-Robert@Honda

Caveat: I work for Honda, but the preceding was my opinion alone.

A no load surge is caused by the idle jet being clogged with dirt or debris. even at full throttle no load the engine runs on the idle circuit of the carb. when you engage the blades the extra load causes the governor to open the throttle which switches over to the main/high speed jet in the carb and it runs smooth.

Thanks for the tip. Will ck idle jet Duane

dgrif said:

Thanks for the tip. Will ck idle jet Duane

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I've ran into this problem on many engines including recently an old 14 HP K-series Kohler cast
iron side shaft on a Ford mower. Started good, sit there and idle great, then while mowing
gets progressively leaner and cuts out, barely makes it back to the garage on choke partially on.
Problem w/ the Kohler was the vibration was making the mixture screws move due to weak springs.
I agree with the mechanic who said to make sure the fuel jets are clear. Another case of fuel starvation
was on a 14 hp B&S rider that would start and sputter and die. Problem, fuel metering
valve down IN the float bowl (new design) had a teeny, tiny piece of plastic intermittently
jamming the fuel flow. Carb spray went through it, could see daylight through it, yet the
flake of plastic would somehow cover the inlet and starve it. Finally had to gouge it out
with a wire, then blow carb cleaner through it. Then ran fine. (after 2 hours of aggravation).
Also enrich the main mixture a tad and that could level out the surging.
Good Luck.