Fs600v dying or surging hunting at all throttle positions


LawnSite Member
Hello everyone!

Ive exhausted all my normal resources so I went looking for a new one and found this place for hopefully some fresh ideas. I have a sick mower Im trying to get back running good again. A few weeks ago it started missing a little bit while I was trying to cut a yard. It was puffing a tiny bit of black smoke once in a while so I figured it was either a fouled plug, or intermittent wire issue. I continued mowing since I only had about 20 minutes left on the yard. By the time I was done, it couldnt even pull itself up my dump trailer without dying. I brought it home and parked her for the night. The following day I wanted to mow my yard, so I went to crank the sick mower to move it out of the way. I have a spare x354 so a dead mower isnt a huge issue. Wierdly however, she fired right up. Actually ran so good I mowed my entire yard and a few extra areas. Not a single hiccup. When I finished mowing, I moved her to her normal spot and not in the grass since it seemed she was back to normal.

Fast forward to the next mow date and the spitting, sputtering, and smoking was all back again. I did notice something this time though. If anyone can explain it, please do. Even though the mower was running terrible, and missing, when you turn the key to off, for the 2 second delay it takes before the mower kills the engine, it ran perfectly. Every single time. Turn the key switch to ON and it sounds and runs like crap... turn the key to off and it would run perfect. Turn the key back to on before it shuts down and it would quickly start to die again.. back off, and its smooth as silk until it cut itself off. Something to do with the solenoid I bet. I parked her in the garage and took my working mower to do the job. When I got home I gave her 2 new plugs. Didnt help. I pulled the wires and checked for spark. No problems there, and each time I pulled the wire on either cylinder, the engine increased its miss. Satisfied with the ignition system for now I moved on to the carb. First I wanted to test operation of the shutoff solenoid. It worked as it was supposed to. So I went ahead and pulled the whole carb for tear down and rebuild. After a thorough cleaning of all the components, I reinstalled the carb new gaskets and all. Once gas had filled the bowl, I could tell the miss was gone.. but sadly in its place, was now engine surging.

After manually manipulating the plate on the carb that the governor controls, and mostly covering the intake pipe, I could get it to run semi correct for a moment or two. But left to its own, it quickly dies. I changed the fuel filter and verified the fuel pump was in fact pumping. I also gravity fed the carb just to make sure the fuel system wasnt affecting the mower in anyway. Doubting my work, I kept telling myself its got to be still in the carb, maybe i missed the blockage, or installed something improperly, or something. To try and isolate the issue, I ordered a cheap but highly rated carb off of amazon. This would either fix my problem, or exclude the original carb from the "suspects list".

Today after installing the new carb, I still have the same issue.

Now as it sits, It wont start without full throttle, and even then it surges.

Anyone here ever seen anything like this? Ill admit, im not really sure what to check next. I could sure use some help here!

Thanks for taking the time to try and help!

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