Petrol Lawnmower Hunting And Surging- Help And Repair

How To Fix A Briggs And Stratton Lawn Mower That’s Hunting or Surging

When I first purchased a Briggs And Stratton Lawn Mower, I honestly couldn’t believe it when it started hunting, revving up and down (Surging) and chugging out black and white smoke. It was only a couple of years old!

Luckily I found out why and managed to fix the problem in a few simple steps.

I still use the very same lawnmower  15 years after I nearly scrapped it!

In this article. I will show you how to fix any  Briggs And Stratton hunting and surging lawn mower problems  (for under $10) or for free.

So how do I do this I hear you ask?

There are two types of carburettor on a Briggs And Stratton Petrol Lawnmower and whichever one you own I’m going to show you a quick fix.

Before we start I just want to say the reason your lawnmower is surging and hunting is due to fuel starvation!

You can find lots more information and start repairing lawnmowers for profit by checking out my online training here

Briggs Engines With A Primer Bulb

If your petrol lawn mower has a primer bulb on it that you push to prime before you start the mower, I can tell you with 100% certainty that the cause of the hunting/surging is due to the diaphragm and gasket between the carburettor and petrol tank needing to be replaced. (A lot of people think it’s the little governor springs). It’s not!

This is a simple procedure that should take no longer than 10-15 minutes and you can purchase a new gasket kit very cheaply (I’ll cover this later).

Check out this playlist of videos it covers lots of common issues with hunting and surging.

The only other type of carburettor you will find on a Briggs And Stratton Lawnmower engine is a bowl-style carburettor. (If you don’t have a primer bulb it’s this one!)  In this case, if your petrol lawnmower is hunting you need to simply clean the main jet in the carburettor and I promise your lawn mower will run as good as it did when it was new.

Imagine how learning these 2 small repairs has earned me thousands over the last ten years.

This is how I got into the whole business of repairing lawnmowers for profit.  In this article, I will show you step by step how to undertake these repairs on both types of carburettors and stop your lawnmower hunting and surging and chugging out black or white smoke!

Trust me, once you see how simple it is and have saved a fortune on purchasing a new lawnmower you’ll be amazed.


Replace The Gasket Set On A Briggs And Stratton Lawn Mower

OK, the first thing you will need to do is remove the spark plug from your lawnmower this is the only way to guarantee there will be no accidents! Next purchase a diaphragm and gasket set usually Briggs and Stratton part number 795083 Diaphragm/Gasket Kit.

Remove the air filter box using a flat-headed screwdriver pull out the long screw and set aside. There are only two bolts to remove to get the entire petrol tank and carburettor off the lawnmower.

I have made a Youtube video covering this exact procedure.

Please subscribe to my Youtube channel here

Looking at the petrol tank from the side (longways on facing the primer bulb) there is one 10mm bolt on the right-hand side and a 13mm bolt near the primer bulb.

Undo these two bolts and wearing safety glasses and some gloves in case of petrol spillage, pull the petrol tank towards you.

You will notice once it’s loose there is a little connector linkage still attached near the governor springs, just unhook it and you have the whole petrol tank and carburettor off the lawnmower!

With the petrol tank now removed undo the six Phillips (crosshead) screws from around the carburettor and pull the carburettor away from the petrol tank. In between the petrol tank and the carburettor you will see the diaphragm and gasket.

Don’t Play With The Springs!

Just remove them and dry the surrounding area on the petrol tank. Replace the old gasket set with the new one. Carefully line up the carburettor looking down the screw holes from above and re-tighten. Hook the little linkage back on FIRST then push the carburettor and petrol tank back on the mower.

Note: make sure all the springs move freely afterwards, they should bounce around against each other in a tug of war type way! There are 2 washers on the back of the carburettor a black and a white one, make sure they are seated correctly!

Tighten the 13mm bolt and the 10mm bolt and replace the spark plug. As if by magic your lawn mower will no longer hunt or surge as it’s no longer starving the fuel flow and it will be good for another few years.

You can view a video on replacing the governor springs here 

Note. You can purchase complete carburettors for most Briggs and Stratton lawn mowers complete with gasket sets included. Occasionally the carburettor becomes slightly warped as it’s a plastic carburettor sitting on an aluminium petrol tank. The part number for a genuine new part is Briggs And Stratton part number 795477. This is for a new carburettor and a gasket set.

You can find all the parts required including diaphragm and gasket sets on my recommended parts page here

It’s So Simple

This is the exact procedure I used on my own Briggs And Stratton petrol lawnmower 15 years ago and I have done this repair HUNDREDS of time while repairing for profit. In fact, it’s the number one repair I have to do.

Another quick tip now you know how to make your engine last forever, is to remove the spark plug from your lawnmower and wire brush the grass off the underside of the deck. The problem I see most often that causes people to replace their lawn mower is that the engine is still working long after the deck has a hole in it!!

Servicing A Bowl Type Carburetor

So, what if I don’ have a carburettor that uses a diaphragm and gasket? Well, I promised I could provide a solution for both types so here we go:

The other type of carburettor you will have is a bowl-style it’s probably mostly hidden behind the air filter box on the opposite side to the exhaust (see photo). Remove the spark plug before you start any lawn mower repair.

If your lawnmower has a valve to turn the fuel flow on and off, then you should shut this off now.

If it doesn’t, then remove the air filter and you will see two bolts that go right through the back of the air filter box, through the carburettor and into the engine itself. Remove these two bolts and set the air filter box aside. Now you will be able to see where the fuel line connects to the carburettor.

Take a clamp or a set of mole grips and clamp the fuel line then pull the fuel line off the side of the carburettor. Next, take a photo looking down from the top of the carburettor and be sure to take a few photos of where any linkages connect to the carburettor. Unhook the linkages and remove the carburettor from the lawnmower.

Take a small container and put the carburettor in it and tip it upside down to remove any old fuel. Next, undo the bolt on the bottom of the carburettor and take off the bottom bowl part of the carburettor.

Don’t lose Your Needle!

You will now see a needle attached to a float just pull out the retaining pin and move the float out of the way taking care to not lose the needle! Looking from the bottom you will see the main jet, you will need a small flat-headed screwdriver to remove it. Unscrew the main jet and take a look at all the tiny holes!

Take some carburettor spray and give everything on the carburettor a good spray up. If you have a compressor you can blow everything out with compressed air but if not you can get a can of compressed air to do the same job very cheaply.  Note if the main jet doesn’t drop out after unscrewing it you can use an Allen key to push it down from the top!

Check out this video on how to service this type of carburettor.

Please subscribe to the channel here

Make sure everything is completely clean and dry and re-assemble the carburettor. Hook the linkages back on top of the carburettor FIRST before sliding the carburettor back onto the lawnmower. Re-connect the fuel line BEFORE you fit the filter box otherwise, you probably won’t be able to access it! Refit the bolts through the air filter box refit the air filter and re-fit the spark plug.

It’s as simple as that no special tools required! Believe me doing this makes a massive difference to the running of your petrol lawnmower, if it doesn’t get the correct flow of fuel it will hunt and surge plus it will be difficult to start.

Extra Tips For Stopping Your Lawn Mower Hunting And Surging

There are a few things you can do to avoid having to do this small maintenance procedure so often.

Visually inspecting the petrol tank is a great idea, take a look to see if there is any debris floating around or any rust in the metal petrol tank. All these little pieces will find there way into the carburettor and cause hunting problems.

Never ever run your lawnmower until it runs out of fuel. The reason for this is all the dirt and crud that has settled to the bottom of the tank will be sucked through the carburettor.
Use the best quality fuel! This may sound a little ridiculous but think about how long you usually store and use that fuel compared to using it in a car!  The reason you want the best quality fuel is simply that it lasts longer in storage.

Take a look at this video for example

Use a filter. When re-filling your petrol tank use a filter. The reason for this is it will help keep any dirt out of the container transferring to the petrol tank!
Buy a quality fuel storage container.

If you do this the petrol will maintain it’s properties longer but the main reason is not to spill a single drop when re-filling your lawnmower. This is particularly critical if you have a lawnmower with a diaphragm and gasket as you don’ want any fuel spilling over the plastic carburettor.

Don’t Mess With The Springs!!

I have repaired so many lawnmowers where someone has tried to stop the hunting and surging by stretching the springs! I’ve seen all sorts of various contraptions! It doesn’t work. Ever.

You may also want to check out my complete guide to repairing lawnmowers for profit. You can find it here

If you are still having difficulty with running problems you will need to take a look at the ignition kill switch.

You can see my article here

You can find lots more information and start repairing lawnmowers for profit by checking out my online training here

I promise once you use this information to repair your own lawnmower it will be very tempting to get another one to repair for profit! If so take a look at the home page or the recommended products section of the website and you can see all the tutorials and courses we have to offer.

Happy Mowing!


Recent Content