4 hp briggs and stratton mower


Old 05-09-11, 06:44 PM
Thread Starter
Join Date: Jan 2011
Location: canada
Posts: 87
4 hp briggs and stratton mower

I have a 4hp brigs and stratton mower.

I picked it up as a no start. About 8 years old.

The carb is a plastic carb located on the tob of the metal gas tank. Pretty basic set up. I cleaned the carb, reset the ignition and cleaned it right up.

Started first pull. ran not too bad, then started to falter.

I put new gas in as well.

I noticed when it was running that there was oil spitting out of the hose attached to the carb. Never seen this before. Must explain why I am seeing smoke out of the exhaust as she begins to falter.

Any idea why this oil is leaving the engine and hitting the carb? Is this not for a vaccumm? Trying to understand the function of that hose into the carb from the engine???

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Old 05-09-11, 07:43 PM
Join Date: Jun 2006
Location: St. Louis
Posts: 2,365
The hose is the crankcase vent, it could send oil to the carb if the engine oil is overfull, the engine has been tilted with the carb down or the engine turned upside down.
For the surging:
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
Old 05-10-11, 06:42 AM
Thread Starter
Join Date: Jan 2011
Location: canada
Posts: 87
Hi Geogrubb,
You seem to be the resident mechanic.

I have taken apart the carb before so am very familiar with the diaphram etc. I was not aware the plastic jet could be removed. I was also not ware the stem could be removed. Thank you for educating me on that.

I will replace the diaphram with the kit out of Lowes. All good, I will have that done tonight.

I checked the oil level this morning. The oil is very dirty(expected) and is bang on for level.

If the mower was tilted etc, how long will it take for the oil to stop coming out of the crankcase vent. Can I clean it out? Id like to stop the oil from entering the carb. Certainly cannot be good for cleanliness. I notice the engine falter as the oil begins to spit into the carb from the Crankcase vent tube.


Thank you,

Old 05-10-11, 07:12 PM
Thread Starter
Join Date: Jan 2011
Location: canada
Posts: 87
Thank you for your post. You wer bang on. I took a carb and tank of an old mower I had and exchanged them. It runs like a screamin chicken. I am sure it is the diaphram. Ill get one of those and pout the new diaphram on the oldmower.

Good job and great help. I am learning every day.

Until my next post, thank you.

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