# Briggs & Stratton 500 Series surging



## PipePlayr (Oct 30, 2008)

Hey guys,

I have a B & S 500 Series, 158 cc, walk-behind auto-throttle mower that is "surging". The engine speeds up like when going through tall grass and slows back down again. The problem is, it does this under no load. It is also drinking the gas like crazy.

The only numbers I found on the engine are on a barcode: 0709265460775

Does anyone have any ideas what's causing this and how to fix it??

MANY thanks !!!!!!!!!!!

Vic


----------



## 30yearTech (Sep 14, 2006)

The model number is usually stamped into the blower housing and painted, so it may be hard to see.

Is your carburetor mounted above the fuel tank? If so, then you likely need to replace the diaphragm as it could be leaking allowing fuel to bypass the metering circuit and drawn directly into the intake, causing excessive fuel usage and the running issue you describe.


----------



## geogrubb (Jul 28, 2006)

If you have the model with the plastic carb setting on the fuel tank, the following applies;
You need to install a new diaphram kit, it is Briggs part # 795083 or old # 495770 also Lowe's has a kit #5083 which has the same parts.
Here we go;

Remove air cleaner, there are 2 bolts that hold things together, one on the front of the tank 3/8" and one into the block 1/2", remove these bolts, now "slowly" slide the carb/tank off the intake tube and breather tube, now tilt the tank in to release the throttle linkage and waalaa the carb/tank is removed. Check the intake tube to see if the “O” ring seal and plastic retainer are still on the intake tube, if so remove them and re-install them into the carb. Remove the 5 screws from the carb/tank remove carb(don't loose the spring) now spray all holes, cracks and crevases in both the carb and tank surface with brake parts cleaner, remove the main screen(looks like a thimble), now with a small screwdriver pry out the main jet(carefully) and clean it, check the “O” ring on the main jet for damage, if it is damaged it must be replaced, reinstall the jet, it can be difficult some times to get it to snap back in place(I use the rounded end of a screwdriver handle). Remove and clean the fuel pickup stem(not necessary if the fuel tank was clean). Clean any junk/rust from the tank. Install the diaphram on the tank then the gasket(no goo or sealer) now carefully replace the carb(the spring will try to misalign the diaphram), tighten all screws a little at a time so as not to crimp the diaphram until they are all tight. Install the carb/tank in reverse order and you are done. If I missed something one of the real mechanics will correct me. Have a good one. Geo


----------



## PipePlayr (Oct 30, 2008)

I found the correct model numbers: 10T502 3764 B1 07092655

Thanks for the replies!


----------



## geogrubb (Jul 28, 2006)

PipePlayr said:


> I found the correct model numbers: 10T502 3764 B1 07092655
> 
> Thanks for the replies!


Follow the instructions provided above. Have a good one. Geo


----------

