This may be "apples and oranges," but here's some info.

I have a 7.5 HP Briggs on a rear tine tiller, from it's second season on, it surged and hunted badly. Played with governor settings, there are no carb adjustments, nothing helped. Finally with info obtained here, I partially disassembled the "non serviceable" carb and sprayed it very well with carb cleaner, did that a couple of times. Totally drained the tank and refilled with new gas which had Stabil added, also some carb and fuel injector cleaner. Couple of tanks later the problem had essentially disappeared. This pretty much proved to me that my issue was caused by the "mystery fuel" available at the pumps today. Now I'm rabid about fuel conditioners. Stabil or equivalent goes into the empty can before it goes in the back of my truck to make a fuel run. I've actually bought a shut off valve for that tiller so I can run it dry after use, just haven't got around to installing it yet.

I'd look into what parts you get in the carb rebuild kit, you may have to replace the carb, as the issue is probably in the jets. I know Sears now automatically replaces those carbs as there isn't a lot you can do to them.

Just my two cents,

Good luck,

Ev

Hold the throttle shaft steady with your finger, if it smooths out and runs steady the governor is too sensitive. If it stumbles and fights you have a carburetor issue or intake air leak.
Spray carb cleaner around the base of the carb and the manifold gaskets on the head while the engine is running, an air leak should show up.

My surging problem was cured by changing the fuel filter.

Regarding carburation in general, usually this is a fuel starvation issue. In almost all of these cases, I've soaked the carbs in NAPA carb cleaner and they end up working great. Disassembly is necessary, along with an air gun, and removal of welch plugs. Sometimes you can do it without removing all the welch plugs.

Lot of ifs. Model and spec?

Kudos to romore, I forgot to mention that I did that. The engine didn't settle down as it normally would when you hold the throttle.

Ev

"Spray carb cleaner around the base of the carb and the manifold gaskets on the head while the engine is running, an air leak should show up.

Isn't that kind of dangerous? I have never saw nonflammable carb cleaner. I use a spray bottle with water and a little soap to do that.

***"I use a spray bottle with water and a little soap to do that."***
Please tell us what kind of results you are anticipating by spraying a non flammable liquid onto a seam suspected of having a VACUUM leak.

"Please tell us what kind of results you are anticipating by spraying a non flammable liquid onto a seam suspected of having a VACUUM leak."

The soapy water will temporarily stop the leak.

Soapy water for expected PRESSURE leaks - makes bubbles

Never heard of using that for a vacuum leak. Have always used spray carb cleaner - far easier to hear the sudden increase in RPM's, than a slightly better running engine when the leak is plugged temporarily.

***"far easier to hear the sudden increase in RPM's, than a slightly better running engine when the leak is plugged temporarily."***
Hear Hear!

I guess you have never had your eyebrows burned off? I have, by someone unexpectedly spraying carb cleaner on a hot motor! Sorry but I believe in safety first!

What if your advice caused the OP to get hurt or worse? Would you feel bad? Advising someone to do something that dangerous is not good.

How much alcohol is in your fuel "up there"?
IF it's more than 10%, you may need a bigger Main Jet(s) in the carb.

Engine Model & type#'s are handy to know so one can see exactly which carb you have etc.

Must be using exxon gas that crap has a bunch of water in it. I filled 10 1G jugs and got 2G of water out of them.

Must be using exxon gas that crap has a bunch of water in it. I filled 10 1G jugs and got 2G of water out of them.

It's actually difficult to find water in the gas when freshly purchased. The alcohol absorbs it.

Just sounds like some kind of rant from a BRAND NEW POSTER!

We have 26hp briggs stratton v-twin it surges up and down u pull choke out run pertty good we dun clean carb two times what u think it could be we set the governor like it but will still idle up more eidle up it ben a nightmare it was running good he was mowing with deck belt pull in garge and know it won t run right it new plugs and fuel pump he set values on too

Quote "I have a new b/s lawnmower" Assume new not a newly purchased use machine. If it is New, I would take it back to the dealer. If it is new it should be under guarantee.

Why spend a lot of time with it let the dealer deal with it. It may be a lemon, and if you try to fix it it could invalidate the guarantee, and you would be stuck with it.

The best way i have found to check for vacume leaks is a small propane torch like the ones used to solder copper pipe. Just turn the torch on but don't light it. Hold to tip close to the suspect vacume leak you will get a increase in rpms if the is a leak. No buent eyebrows.

Great tip. thanks.

Start with the basics. Air, Fuel, Spark. One time I had "surging" the air filter was dirty. Before that it was the fuel cap; centering the gasket solved the problem. Most recently it may have been only hot humid weather (vapor lock?), but cleaning the exhaust recirculation port in the air cleaner and repairing a leaky fuel hose seem to have solved the problem. Surging seems to be due to a cumulation of problems, and simple fixes may have more effect than adjusting the governor or carburetor...

I fixed mine by changing the spring on the throttle to the carborator.

Spring was too weak.

Found this cap missing on our one causing bad surging issue. (see photos) fell out mid way through mowing the lawn.

Located behind the mounting bolt.

I noticed on a 26HP V Twin Briggs and Stratton with a manual choke system be careful when adjusting or installing a throttle cable. In Max run mode be careful cable doesn’t start to apply choke or engine will begin to hunt. On this engine choke is applied when you apply throttle forward of Max RPM run mode.

why ask for help and then criticize the advise given everyone who works on almost any engine would use that method to find a leak the one that's performing the process is suppose to have enough sence of where to spray at smh