Pulsing lawn mower

The condition is called "hunting", and is caused by a governor that needs adjustment

Loosen the gas cap a tad and see it runs better. If so the cap vent is clogged. Use a paper clip to clear the cap vent hole.

A fouled spark plug might be the culprit.

I have a rototiller that suffers from that problem -- any link to a site that explains how to adjust an air vane governor? I Googled, and found plenty of info about adjusting mechanical governors, but didn't find anything about air vane governors.

The governor is just one possibility for hunting, any number of carburetor issues can cause it as well. In the op's case, it appeared that the engine was fine until they tipped it over, so my guess is that they inadvertently mucked up the vane linkage. I have a pdf I can send you with a typical B&S vane adjustment, just email me at snipped-for-privacy@live.com

Or, it just might need cleaning. On my old Toro, it started hunting. I found the governor lever caked up with mud, grease and grass. After a cleaning with a degreaser (spray carb cleaner) to remove old grease, etc., it ran perfectly.

More often than not, that's just the kind of adjustment they need. Damn things are very critical, so it doesn't take much to throw them out.

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One lesser possibility given it's not terribly old but alternative to the governor hunting is a variable air leak--loose intake or worn throttle shaft are most common of those.

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Im just a tinkerer when it comes to small engines but Ive kept mine going over the years. Whenever I have seen this I just go over them checking everything. First thought usually is that its a governor problem but I dont think I have ever seen that be the problem. Clogged fuel path seems to be pretty common and a lot of "I dont knows" it just starts working after cleaning everything up. I did find one that wouldnt work with cap on. The cap didnt have a vent in it so I figured it had to be vented some place else. I had taken everything apart and cleaned and put it back together figuring this shouldnt be a problem. Well the problem was it had the wrong cap on it. I walked down to my brothers house and checked on the back porch. There was his gas can with the lawnmowers cap on it.

Jimmie

I took another look and I think the little silver spring is installed wrong. I believe it should be attched loosely in the big loop on the throtle linkage.

Jimmie

Maybe dirt lodged from tipping in the governor and linkage, easiest is try compressed air to blow out everything and see if all moves freely.

When I took a small engine repair course, I was told that hunting is caused by a governor spring that's stiffened up.

Replace the spring between the throttle and the vane.

Priceless!

Critical is right. The shaft only moves a few degrees. It doesn't take much to make it work poorly.

Come on dude. Check -The First Baptist Bar & Grill

It seems that every time I let someone borrow a gas can, it is returned sans cap. It's always the same. "Where's the cap?" "Eye-O-no". I think that's one reason Tasers were invented.

TDD

It appears that your linkage has been modified. Go to the B&S website and download the PDF file that will show the proper parts. Then install the proper parts correctly. The linkage that the arrow is pointing to is not the correct part. I am not sure about the springs.

Hank

Try replacing or cleaning the muffler,I have this to be the problem a lot of the time.

Indeed it is. :-)