I agree that cleaning the air intake and replacing the filter may help. I'd
also suggest making sure the carburetor intake is clean and the mixture
adjustment is set properly.

Also make sure all the linkage spring are in place too.

If I had to guess, I'd say that the mixture may be too rich (or lean) and
the engine's governor is keeping it alive.

Good luck!

Bob

"cnctut" wrote in message
oups.com...

spongehead wrote:
I have an old Briggs and Stratton 3.5hp push behind lawnmower and the
idle revvs up and down constantly. Never idles normal. The spring
on
the shaft idle looks good. Any help on what this might be would be
greatly appreciated.


Spongehead--

Recommend cleaning the air intake sponge first then let us know if the
problem still exists. I assume you have the 99 dollar Walmart mower
with no variable throttle.

Tut