Surging / Hunting engine....tried many things but at a loss now and advice would be appriciated

[Eshezo]

So, I have an ATCO lawnmower with a Briggs & Stratton 675 engine.

When I start the mower it starts first time, hunts a little but warms up and starts running smooth in a minute or so, after a few minutes of running smoothly it starts surging / hunting.

Things completed:
1/ Carb cleaned and re-fitted
2/ Petrol tank and pipe cleaned and re-fitted
3/ Fresh fuel
4/ New Spark Plug
5/ Choke / thermostat checked and all working fine
6/ Checked the governer linkage and spring all free and fine.

Here's the thing, when its surging / hunting if I hold the throttle (ie stop the governer moving it) it runs smooth at both idle and revved so I'm quite sure there is no fuel issue. I'm also quite sure the actuall giverner is ok because it runs smooth for a time before starting to surge / hunt.

I've run out of things to look at so any advice / suggestions would be appriciated.

rgds

 

[ILENGINE]

Sounds like a governor sensitivity issue. Can you give us the model number of the Briggs engine. Some of those engines have two governor springs and if they get out of adjustment can cause the surging that you are experiencing.

 

[Eshezo]

Sounds like a governor sensitivity issue. Can you give us the model number of the Briggs engine. Some of those engines have two governor springs and if they get out of adjustment can cause the surging that you are experiencing.

Hi, I don;t have the engine number handy (need to go out to the workshop to check it) but it's not the type with 2 springs, it has a single spring on the governer from front to back on the conecting linkage and then the governer lever which crosses at the back of the engine. it's a 673is insta start which are all the same configuration