Lawn Boy 10301 Throttling/Carb Issues

[Farmer_Mark]

Hello, I've got a Lawn Boy that doesn't throttle evenly. It doesn't make a difference if it's just sitting idle or mowing grass, it always revs up and then backs off over and over. The carb has been dismantled and cleaned several times along with air filter, gas changes and treatments with SeaFoam.

Still there doesn't seem to be a fix my dad or I can figure out.

I took some video of my dad mowing so hopefully someone had the same issue fixed.

 

[Rivets]

Time to have the carb cleaned and rebuilt. With that carb it’s not real hard, but reassembling the carb on the engine is a PITA unless you have done it many times. You have a good unit so if you don’t feel you have the skills to DIY I would pay to have it done.

 

[FuzzyDriver]

Won't vane or vane spring issues cause this problem, too, Rivets? Might be worth looking at first.

 

[tom3]

Does sound like a lean out condition. Dies out, throttle goes wide open, enrichment port opens up. I'd guess you're missing a small port or jet not getting cleaned out in the carb.

 

[Rivets]

You are hearing the air vane and spring doing their job, opening the throttle when a lean condition is felt.

 

[FuzzyDriver]

Now I remember how the vane & spring can cause this. Not saying this IS the problem, but it is something to consider. The spring needs to apply a smooth pressure against the vane pressure. On one of my mowers the spring acted against the vane only at the high and low end, making it a sort of on-off thing instead of a smooth throttle. Mine was the wrong spring.

 

[Fishnuts2]

Hello, I've got a Lawn Boy that doesn't throttle evenly. It doesn't make a difference if it's just sitting idle or mowing grass, it always revs up and then backs off over and over. The carb has been dismantled and cleaned several times along with air filter, gas changes and treatments with SeaFoam.

Still there doesn't seem to be a fix my dad or I can figure out.

I took some video of my dad mowing so hopefully someone had the same issue fixed.

Mine ran just like that until I removed the carb, cleaned the jets, both pilot and main jet, and reassembled it properly. There was a lot of water in the float bowl on mine, but yours should be clear of that if you had it apart already.

The biggest thing to watch is to make sure the “pin” on the choke part of the air box throttle linkage is engaged with the choke butterfly properly. Mine was assembled wrong with the pin setting on top of the butterfly arm instead of in it. This caused the choke to malfunction, and the governor spring had the wrong tension resulting in the fluctuations. As was mentioned previously, it’s tricky to get everything back together properly.

I’ll try to get a picture of the linkage for you.

 

[1saxman]

Regardless, its been a long time since I heard that sound, and it reminded me of how utterly boring my 4-cycle LBs are. I've been itching for another real LB for some time now, but I want one with the under-deck muffler so I can get 'that smell' along with the sound.
Yours might just have a broken governor spring in the base of the air vane - that little spring connects to the slider on the air box.