Briggs & Stratton 725EX 163cc

[Brandi]

I'm fairly handy and enjoy picking up mowers at estate/yard sales and getting them up and running. I've done about 12 this season with good success. I have a Briggs & Stratton 725EX 163cc on a Troy-Bilt mower. I've disassembled the carb cleaned it thoroughly got it running but terrible up & down surging. Replaced the carb with a new one and put in another that I had laying around and have the same issue. It fires right up on a half a pull but I still can't get past this surging. The governor lever & spring are fine. I'd really appreciate any thoughts.

 

[ILENGINE]

Could you supply us with the model number info on the engine so we are not guessing what setup this engine has. Could be a governor sensitivity issue causing the surging or due to misadjustment of the governor spring system.

 

[Brandi]

Could you supply us with the model number info on the engine so we are not guessing what setup this engine has. Could be a governor sensitivity issue causing the surging or due to misadjustment of the governor spring system.

Briggs and Stratton 104M02-0010-F1​

 

[ILENGINE]

Check the engine speed. If trying to run too fast or too slow may cause surging with the fixed speed carbs. You can try holding the governor steady and see how it runs. If it runs smooth then related to governor sensitivity or engine speed, if runs poorly then carb related with running too lean.

 

[slomo]

I've disassembled the carb cleaned it thoroughly got it running but terrible up & down surging.

Carb still dirty or trash in the fuel system.

Replaced the carb with a new one

Amazon or Ebay carb?

put in another that I had laying around and have the same issue.

Was this the OEM carb for this engine? If so it's dirty too.

The governor lever & spring are fine.

Explain what fine means. You see one present? Is it hooked up proper? Wrong spot maybe? Wrong spring in there from a hardware store?

Surging is either a vacuum leak, dirty carb (most likely) or trash in the fuel system (highly possible).

Clean your cooling fins and adjust the valves while you are at it.

 

[Brandi]

Check the engine speed. If trying to run too fast or too slow may cause surging with the fixed speed carbs. You can try holding the governor steady and see how it runs. If it runs smooth then related to governor sensitivity or engine speed, if runs poorly then carb related with running too lean.

Thank you sir for your suggestion. I will try both. Governor sensitivity is the perfect term. I'm retired an just like tinkering with these rather than see them thrown away. I keep my tinkering to the basic law mowers and shy away from anything other than that. Again, thank you.