Pulsing lawn mower

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Howdy!
I just received a three year old B&S 3.5 horsepower mower from a friend. Currently, it starts easy but starts pulsing once it's been running for a few minutes.
I've been told that the mower ran fine until it was tipped onto it's side to be cleaned out.
What I've done so far... - cleaned the sponge air filter - drained the gas and filled with new - sprayed the carb with carb cleaner - checked oil levels - ensured that the throttle moves freely
The only thing that I can think of is that it's internal to the carb, or that the springs on the carb are not in their correct location.
Photo's of the carb and linkage.
http://members.shaw.ca/linkto/temp/carb1.jpg
http://members.shaw.ca/linkto/temp/carb2.jpg
Any ideas on how to fix this?
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The condition is called "hunting", and is caused by a governor that needs adjustment

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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.
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Replace the spring between the throttle and the vane.
--
Christopher A. Young
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RBM wrote:

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.
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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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RBM wrote:

Critical is right. The shaft only moves a few degrees. It doesn't take much to make it work poorly.
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When I took a small engine repair course, I was told that hunting is caused by a governor spring that's stiffened up.
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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.
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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
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Priceless!
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On Sun, 9 Aug 2009 21:49:22 -0400, "Stormin Mormon"

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

http://www.youtube.com/watch?v=YliBqsV3YMc

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Stormin Mormon wrote:

Indeed it is. :-)
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JIMMIE wrote:

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
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wrote:

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

Same thing hapened to a fellow at work. He said his riding mower would start and make about a round of the yard and quit. I asked him to check the vent and the next day he reported back that he had mixed up his gas can and mower gas cap.
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Calab wrote:

...
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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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
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wrote:

to
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
If it's what I *think* it is it should have only the slightest tension when the engine is stopped. Is it a very weak spring about 2 inches long (or so)?
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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.
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