# Briggs Quantum, Surging and air filter



## twomey (Jun 15, 2005)

We have a Toro walk-behind mower with a Briggs & Stratton Quantum engine. We have had a problem with surging since first starting it up this year. We cleaned and rebuilt the carb (using the Briggs kit). Still surging. My wife washed the air filter (which the manual says not to do), and the surging when away. So We stopped at the dealer and picked up a new filter. The new filter looks the same and the part number is the same except it has an 's' at the end. Fits fine. When the new filter is put in, the surging returns. Put the old washed filter in, and the surging goes away. Anybody have an idea what would cause this?

Thanks,
Tim


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## bugman (Aug 12, 2004)

the old air filter that was wetted down, is probablly stuck up alot more then the new one. it sounds like the governor is causing the surging. and the old air filter is starving it for some air calming it down, kinda like if you take your hand and cover most of the carb opening and it calms down. try holding the governor if you can, it may calm down some or all the way.


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## Denali60 (Aug 6, 2005)

*Briggs & Stratton Surging*

Here's my successful experience...

My mower: MTD mower, about five years old, Home Depot. 4HP Briggs and Stratton 10A902 model engine, part of the 10A900 model series, automatic throttle.

Symptoms: Initially, for a few seasons, engine would sputter when pushing mower back and forth. Then at the start of the next season, the engine would surge, the automatic throttle gunning the motor over and over. It runs, but it sure makes you look like a dope mowing like this. You'll see the automatic throttle lever with two springs moving back and forth while it's surging. (By the way, the fan for the air-cooling of the engine blows air against a lever. The lever, connected to those springs, is your throttle; less air, mower speeds up; more air, mower slows down; proper amount of air, mower runs fine. You'll see this gizmo if you remove the top covers of the engine, which is very easy to do.)

Solution: Replace the gasket-like membrane (part number 495770 for my engine) between the carb and the fuel tank. $2.95 part cost. The membrane lets fuel sift through it, from the fuel tank to the carb, and a gasket is sandwiched with it.

Why does it fail?: Poor design. I'm not an expert on this stuff, but there's a 1/4" diameter spring pushing against the membrane, and over time (about two years in my case) it pushes the membrane far enough where the membrane is no longer sealed by the gasket. The replacement part is slightly larger in the area of the 'failure.' 

Future Insurance?: When I installed the new membrane/gasket, I put some liquid gasket product around the gasket & membrane in the area of the failure, being super careful not to put too much on, or spread it into the other holes and flaps.

Cautions: One of the small springs connected to the carb broke upon reinstall. I just cobbled it back together. Also, there is a metal tube connected to a rubber elbow, and then to the carb. The metal tube goes across to the far side of the engine, where it partially broke; I gasket-sealed the thing in place. 

Procedure:
1. Remove air filter.
2. Remove carb and fuel tank as one unit.
3. Detach carb from fuel tank.
4. Look for 1/4" diameter spring pushing against the membrane. This was the trouble area.
5. Clean carb, tank, gasket areas, and reinstall. If you used gasket sealant like me, wait one day before gassing up and testing.

For pics, email me at: [email protected]

Lance :thumbsup:


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## bugman (Aug 12, 2004)

well, the quantum and the quattro? right. if it uses the carb thats mounted right on the metal tank, that membrane is the diapragm, and yes they can usually last a few years and need replacing once in a while through the engines life, since it is what controls the gas, the gasket is there to seal it up, and then of course a warped tank can cause it to suck air and well.....you won't get much. that lever... is the wind vane governor, quantum's use a internal governor. the windvane governor on these newer ones should have 2 springs, and one link, older ones was one spring. the springs can get rusty and break or stretch or both, also make sure the windvane moves freely. and that spring there you were talking about on the membrane, well they also do wear out, but only on these little diapragm carb engines. (what gasket sealant)?? didn't really need it, but i guess it would do. but screwing the carb down good and tight (if its not warped etc.) it should seal tight. also the metal tube with the rubber elbow that hooks to the carb on the side....it comes from the breather on the other side, and hooks to the carb. kinda hard to get off if you are not taking the carb off. though those elbows are easily replaceble, they over time rot, and crack up. if it has no throttle control, on the handle bars, or on the front like the classics, then all it is set to do, is run full throttle, all the time.


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