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Hello All:

My 5239 mower surges or hunts during use. It starts on the first pull but acts as if it is starving for fuel. Adjusting the needle makes no difference as I can turn the needle until it hits the bottom of the engine and no change! I just rebuilt the carb so it is very clean. The surging is why I rebuilt the carb!

Should I open the main jet by drilling it to a larger diameter? If so, how much? If this is not the fix, what else should I consider? The fuel is 16-1 and is fresh. Could fuel with excessive oil cause this problem? It really produces a large amount of smoke!

Perhaps it is not a fuel problem. Perhaps the governor is sticking or is loose or...

Suggestions and or comments?

Stay well,

Franchi

Before doing that, did you remove the main nozzle and clean it?

You have a D-400 series carb, this manual may be of some help. https://lookup3.toro.com/ttcGateway/acrobat/manuals/lball10.pdf

Yes, everything is clean!

The fact that the needle Has NO effect on how the engine runs has me stumped. It has always worked in the past. A needle and seat can not be a mystery, can it? Turn it in= less fuel. Turn it out = more fuel! In this case, the needle does not make any difference.

What is happening?

Stay well,

Franchi

Yes, a too rich fuel mixture can be the problem. You might want to try the synthetic 2-cycle oils, which will change the mixture, but still keep the oils protection properties. I use Opti-2.

I am now thinking that the fuel was stale. I mixed a batch of fresh fuel, and the problem ceased.

It is now a sweet running 52339!

Thanks for the replies.

Franchi