Briggs & Stratton 4 HP engine surging...

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  #1  
Old 05-26-13, 12:03 PM
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Briggs & Stratton 4 HP engine surging...

I have a Briggs & Stratton 4HP engine on my push mower.

It was running fine then suddenly it started surging. I've run it for about an hour since and it has been fairly consistent in its surging. Only a couple of times did it smooth out - and only for a few seconds.

The carb has no adjustments except for what I call the throttle - the owner's manual calls it the "governor control lever." Adjusting this lever does vary the engine speed, but the surging remains at any speed.

The air filter is clean and the bowl appears to be clean.

Any ideas on what the problem could be?

Thank you!
 
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Old 05-26-13, 12:57 PM
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It's likely a dirty carburetor.

Even though the float bowl is clean there are tiny holes for metering fuel, jets, that can clog. It can be anything. Dirt or old gas are likely culprits. Usually the surge is caused by it being lean.

If you haven't, drain all the gas out and put in fresh, as in you just got it from the station, fuel. Gas goes bad in as quick as 30 days.

If it's running somewhat well you could try running a fuel system cleaner. Odds are the carb will need to be taken off and cleaned.
 
  #3  
Old 05-26-13, 04:30 PM
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To clean this type of carb, do I need special cleaner or do I just take it off and make sure the holes are clear with the help of some gasoline?
 
  #4  
Old 05-26-13, 05:37 PM
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You'll probably need something stronger than gasoline to clean it. Get some spray carb cleaner. Do you have compressed air to blow out the carb?

You can use something like the bristle off of a wire brush to clean the jets. Make sure the float is pivoting freely as well.

Before you take the carb off, take lots of pictures of the linkages. They can save you a lot of grief later.

What are the engine numbers?
 
  #5  
Old 05-26-13, 06:56 PM
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I appreciate your help aandpdan.

I do have an air compressor.

What are the engine numbers?
Do you mean the model and serial numbers?
 
  #6  
Old 05-26-13, 09:49 PM
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It would be nice to have the Model, type and code numbers usually stamped in the metal shroud just above the spark plug, however.
If you have a fairly new B&S 4hp engine the carb sets on top of the fuel tank and the instructions below will explain how to fix it.

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
 
  #7  
Old 05-27-13, 01:27 PM
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Do you mean the model and serial numbers?
Yes, that's what I mean. Briggs makes many engines and can have many different carburetors.
 
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