Just inherited a Briggs mower that revs, then almost dies, revs, then almost dies. Then, as it was running out of gas, it ran hard like it should until it emptied. Did this twice. Air filter OK. Is this a carb issue? Any help greatly appreciated. In the last three months I've had a broken drill, garage door torsion spring, humidifier, glasses, other mower, sprayer, and many things I'm sure I've forgotten, so any help on how to keep from going to another repair shop would be greatly appreciated.

OK, what hp, 3.5, 4.0,4.5, 5.0... what... is it a quantum, classic or what. OK now does it run good for a while and rev up and down, or go up and down, up and down continuously, well, if it is a quantum with a fixed engine speed, or not. The governor shaft could be sucking air, requiring someone with experience to fix, or it could be the governor spring is worn out, and needs replacement. And you say it runs good until just before it runs out? Well for one thing, make sure the filter, if it hasn't been replaced for a couple years, to replace it, one of those tune up kits would have it all, filter, oil and plug. Or buy them separate. Now if it runs great, not running over what its top rpm limit was set, before it runs out, well, yeah carb may have some crud in it, stopping up a hole.

I knew someone would make me get my flashlight and go out to the shed.

3.5 classic. 11A-020B000

No it does the opposite. I start it and in under a minute it revs and drops, revs and drops. I took off the air filter compartment and applied pressure to the springs and got a higher rev, but still cycled between high throttle and again dropped. There are only 2 springs... I'm not the original owner and no manual so I can't tell you if its missing a spring. As for if one is worn I don't know.

Then I noticed that in the last "minute of gas" it runs strong. As it should.

Last time I mowed with it it had done this reving/dropping thing after several starts. Then suddenly it purred like a content woman. Mowed everything with no problem.

Yesterday back to the cycling thing. Was the neighbors mower and it did the same cycling thing for him until he gave up and gave it to me.

3.5, that's a great easy one to fix, OK, one thing to do with them, they have a pulsajet carb, and the diaprahms are simple, and very cheap to replace, and also make sure the tank is clean, and the pickup tubes at the bottom the mesh screen is clean. Then move on to the springs, then again this engine uses a windvane governor, make sure the flap (windvane) moves freely, and that the springs there, should be one spring on older ones, newer ones use 2. which then again, those springs are very very cheap to replace if they are even worn out any at all. That goes through basically all things that could go wrong with thos classics, besides the coil, or an air leak. But it runs great at last, so it shows none of those right now. Though I'd suspect the carb right now, the newer ones use a plastic carb, but are very cheap to work on. It may have gotten some trash in the tank, and since these can't have a fuel filter, the fuel pickups use a mesh screen to filter the big stuff, and can get clogged. Oh and make sure you have some carb cleaner and blow out all holes. You can leave some gas in the tank, slosh it out, and dump it somewhere safe if you can, to remove any trash in there.

Thanks for the help. We'll see what happens this weekend.