How To Service A Briggs And Stratton 450E 500E or 300 Series Petrol Lawnmower Engine

Servicing a Briggs And Stratton Engine has never been easier.

The new style engines such as the 300 Series 450E and 500E basically have the same set up with one simple linkage to the carburetor and one governor spring.

This is great news for anyone wanting to service their own lawnmower from home, you don’t even need any specialist tools and later on, in this article I’ll reveal a “killer tip” to resolve 90% of all running problems on this type of Briggs and Stratton engine.

In this article, I will share everything you need to know about servicing these great little engines including servicing the carburetor.

So let’s get started.

Before I do any work whatsoever on a lawnmower I remove the spark plug.

The correct spark plug for the Briggs 300 series  450 E and 500 E is BCPR5ES you can find these spark plugs here Spark Plug

Oil, Fuel And The Underside Of Your Lawnmower (Don’t Skip This Step)

If your lawnmower still runs it is advisable to run the engine for a few minutes to warm up the oil as it will help extract it more easily.

You may think that tipping a lawnmower up and draining out the oil would be the quickest and easiest way to do it. Actually tipping a lawnmower over or on its side causes terrible white smoke problems.

I like to use my pela oil extractor to remove old oil. You can see what it looks like here Pela 6000

Its a quick and clean way to remove old oil and fuel and eliminates the need to tip over the lawnmower. My extractor also stores the oil until I can dispose of it in an environmentally friendly way.

I suggest using an extractor to remove the fuel (gas/Petrol) at this point. If you are going to sharpen the blade you will now be able to tip up the lawnmower without fuel and oil causing any further problems.

I use a bench grinder to sharpen the blades and just follow the natural angle of the cutting side of the blade to sharpen. You can also balance the blade with one of these clever balancing tools to reduce vibration.

Take a look at them here Blade Balancing Tool

Here’s a full-service video from my Youtube channel on how to service a Briggs And Stratton 450E Petrol Lawnmower.

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When it’s time to replenish the oil the correct oil is SAE 30 Oil. Most lawnmowers take under 0.5 litres of oil so this product is perfect Lawnmower Oil

Be sure to check the oil level using the engine oil dipstick.

You should fully thread in the engine oil dipstick to check the level and be sure not to overfill to avoid white smoke problems.

At this point, if your Lawnmower has a self-drive I suggest removing the belt guard and cleaning all the grass out to prevent future problems. Once all this work is done re-fit the drive belt guard and blade and I strongly suggest if you have some paint to give the underside of the lawnmower deck a paint to prevent it rotting out over time.

Did you know one of the main reasons people purchase a new lawnmower is because the deck rotted?

How To Remove The Engine Cover On A Briggs And Stratton Lawnmower

What we want to do next is service the carburetor, but removing a few simple parts on this type of lawnmower makes this process much easier so stick with me for a moment.

If we remove the starter recoil and the petrol tank from this type of engine it makes this job a whole lot easier. The great news here is that this is simple! To remove the entire starter recoil and petrol tank we only need to remove 3 small bolts.

On the top of the starter recoil, you need to remove the 3  bolts and lift off the starter recoil. This gives us much better access to the carburetor.

If you had trouble removing the spark plug first you should now have better access to it so please make sure it’s removed.

Next, we need to lift off the fuel tank. this is easy as it just pulls up and off the engine without needing to remove any bolts at all.

Before you remove the fuel tank, slide the fuel retaining clip near the carburetor down the fuel pipe, then simply pull off the fuel line. I usually use a pair of forceps to clamp the fuel line but if you don’t have any (why would you!) then simply place a bolt in the end of the fuel line once removed to stop any spillages or drain out the fuel.

You should now have the starter recoil removed and the petrol tank from this lawnmower engine. This gives us great access to start working on the carburetor service and you will clearly be able to see the linkage and governor spring that was hiding behind the fuel tank.

I’ve serviced these mowers many times and this is by far the easiest way to do it, It has further benefits when re-assembling the engine later.

Here’s a video I made on how to service a Briggs And Stratton 500E Petrol Lawnmower

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How To Service The Carburetor On A Briggs And Stratton 450E 500E or 300 Series Petrol Lawnmower

To access the carburetor and remove it, we first need to remove the air filter box cover, the air filter and then the air filter housing, again don’t worry its just 4 small bolts.

Unclip the air filter cover using the plastic tab on the top and remove the air filter cover and air filter.

You will now see 4 small bolts. Two of these bolts are usually 7mm and the other 2mm are 8mm.

Be sure to remember which size goes where. To remove the air filter housing remove the 4 bolts now. You will notice at the top of the air filter box there is a rubber air breather pipe, you can remove this now. Next pull the air filter housing towards you and it will come off.

Be sure to clean all these parts such as the air filter and the air filter box before replacing. There is a small mesh on the back of the air filter box that is part of the primer, make sure this is clean.  You can test the primer by putting your finger over the hole and pressing the primer bulb to feel for resistance.

You can purchase a new air filter for the Briggs 450E 500E and 300 series here Air Filter 

Now you have full access to the carburetor you can pull it towards you and it will come off the engine, you will notice there is only one linkage to remove which is great. Just pull the carburetor towards you and twist it slightly to unhook the linkage. A small amount of fuel may spill out.

How To Take Apart The Carburetor On A Briggs And Stratton Lawnmower Engine

Now you have the carburetor free from the engine we can start to take it apart. Be sure to not lose the brown/red gasket that’s attached.

The first thing you should do is give the outside of the carburetor a good clean. This stops any dirt entering the carburetor once it’s apart. I use compressed air to do this but a stiff paintbrush would also work fine.

Now we need to remove the bowl from the bottom of the carburetor. I always do this over a container so any fuel or small part can be easily collected. There are two bolts on the bottom of the carburetor, you can go ahead and undo them now and place them in a container. Once removed get a flat head screwdriver and prise away the bottom of the carburetor to remove it.

Next, we need to remove the float, this is the large white plastic part. The float has a tiny needle attached to it so be sure to pay close attention to it. To remove the float lift up the silver bridge pin that is holding it in place. Remove the float the needle and the pin and place it in a container. I usually leave the needle attached to the float where possible.

On the top of the carburetor to the right-hand side you will see a white air inlet. You can remove this by pulling it out by hand or carefully with a pair of pliers. This part is important. You need to make sure the hole is completely clean and unobstructed.

Here’s a video that shows how to service the carburetor on a Briggs And Stratton 450E petrol lawnmower

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On the underneath of the carburetor you will see another white plastic part. Go ahead and pull this out with a pair of pliers. This white plastic part has a separate part that looks like little towers that can also be taken off. The 450E has this tower and I Believe the 500E also. Don’t worry if there is only one piece it may vary slightly from model to model.

At this point you have the carburetor completely stripped down and ready to clean. You will need some carburetor cleaning spray and ideally some compressed air to clean out the carburetor.

You can buy cans of compressed air and carburetor spray here Carburetor Spray  Can Of Compressed Air 

Once you have given the carburetor a good clean by spraying some carburetor spray in any tiny little hole you can find and blowing everything out with compressed air you can reassemble the carburetor.

Start by replacing the white plastic part that looks like the twin towers. This will only go back one way so you can’t get it wrong, next place the needle back into the float, and drop the needle and float in place. Next secure the float with the silver pin and refit the lower bowl part of the carburetor using the 2 bolts. Don’t forget to refit the small white outer plastic air inlet.

Killer Tip For The 450E  500E and 300 Series Carburettors

Usually, I’m not a fan of replacing parts to eliminate problems.

In this instance, though I have reason to suggest otherwise. I have a Facebook page where I regularly get questions about this type of lawnmower. Many times people are complaining about the carburetor being plastic/poor quality and having various starting or running problems. The first thing I always suggest is to service the carburetor as it’s such a simple thing to try.

I have noticed on this lawnmower more than any other that more often than not cleaning the carburetor on this type of engine does not fix the problem nearly as often as on some other types of engine.

Here’s the good news, and it’s one of the reasons I’m a fan of these engines. These Carburettors are the cheapest to replace I have ever come across on any type of lawnmower and I’m yet to have anyone with running issues not have their problem resolved by replacing the carburetor.

Currently, they are under £10 which is amazing considering other lawnmower carburetors can be around £40

You can purchase a new carburetor for the 300 series and 450E engine here Briggs 450E and 500E Carburetor 

Here’s where to buy the Briggs 500E Carburetor Briggs 500E Carburetor

Personally I would try cleaning the Carburetor first, however, I know it to be true that changing this part eliminates 90% of running problems on this type of Briggs And Stratton lawnmower engine.

Refit The Carburettor

With the carburetor serviced you can now refit it back onto the engine. Fit the linkage on first then simply push the carburetor back onto the engine. It’s the best design I’ve seen yet. Make sure the black inlet seal and white inlet are sat evenly when you do this and they form a good seal on the inlet manifold.

Now is also a good time to make sure the governor spring that is usually hidden behind the petrol tank is in good condition.

  • Tip. If you bend the tab that the spring connects to towards the carburetor the engine will run slightly faster.

You can purchase new governer springs for a Briggs And Stratton 450E 500E and 300 Series Lawnmower here Governor Springs

Connect The Fuel Line

Remember when I mentioned why I take extra parts off to service the carburetor? Here’s why.

While the air filter housing is off the engine, fit the fuel tank back in position. This is much easier to do with the air filter housing, not in place.

Connect up the fuel line to the carburetor and secure the fuel line clip. Before you replace the air filter housing drop a small amount of fuel into the tank and check the carburetor for leaks. If the carburetor does leak there is a good chance it’s because the needle isn’t seated properly.

Replace The Air Filter Housing

Now we have the fuel line connected and we are sure we have no fuel leaks you can go ahead and re-fit the air filter housing. Use the 4 bolts we removed to do this and don’t forget to connect the breather pipe at the top. Replace the air filter if needed and put the cover back on.

Kill Switch

Checking the kill switch and making sure it’s clean is essential. If the kill switch does not operate correctly your lawn mower will not have spark and, of course, it won’t run.

You can read more about it in this article

Replace The Starter Rope On A Briggs 450 E Petrol Lawnmower

If you would like to learn how to replace the starter rope on your lawnmower you can find more information here

If you are looking to replace your current lawnmower please take a look at my current recommendation here

I hope this article has helped you service your Briggs And Stratton lawnmower engine and don’t forget you can find over 300 free tutorial videos on my Youtube channel

Happy Mowing

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