What causes a Briggs and Stratton 3.5HP engine to surge?

[rkfarthing]

I have a 3.5 HP Briggs on my mower. It worked fine until a friend suggested that it would run better if he shortened the choke spring, which he did. It has run like crap ever since and "surges" constantly (will not maintain a consitent speed).

I replaced the carb spring with the correct one I got from a small engine repair shop. It didn't make much difference.

Any ideas on what I can do to get my faithful old mower back to behaving like it's old self?

 

[ILENGINE]

some of the briggs pushmower engines have two governor springs ( a long one and a short one) if they are out of sync then engine while surge. if you have these two springs take the air cleaner off and take the tension off the small one and then while using a tach set the engine speed to 200 under the recommended rpm by adjusting the tension on the big spring and then retension the small spring to bring the rpm up to recommended and then it should stop surging. if not then you may have to replace the carb diaphragm and clean the carb.

 

[rkfarthing]

Thank you. Mine does not have 2 springs. I'm thinking it has to be something with the carb. Maybe it's the diaphragm as you suggested.

 

[Briana]

Hey there - WELCOME to LMF!

I moved your thread to the Small Engine & Mower Repair Forum. :smile:

 

[benski]

"I'll take "new carb diaphragms for $200, Alex.":wink:

 

[rkfarthing]

Looks like I need to pick up a new diaphragm. Like the Jeopardy twist!

 

[rkfarthing]

Bought a new diaphragm, and primer bulb while I was at it, but that didn't do the trick. While I was spraying down the carb with carb cleaner, after I removed it the 2nd time, I noticed some nearly invisible thread-like stuff on the fuel pick-up tube. Cleaned that up really well, put the carb back on the mower and it ran (runs) like a champ! Thank you for pointing me in the right direction!

 

[benski]

:biggrin: That's great! It feels good to get stuff running like it should:thumbsup:.