How To Service A Briggs And Stratton 35 Classic Lawnmower Engine

The Briggs And Stratton Classic engine is a very popular engine fitted on many lawnmowers all around the world. They are incredibly well built and designed to last a very long time.

If you’re not sure what type of engine you have I’ll show you how to find the serial number, but for now if your lawnmower engine has a red primer bulb and a rectangular air filter box with a triangle at one end, this article will teach you how to service and repair a Briggs And Classic Engine.

Serial Number

To find the serial number on your Briggs And Stratton Engine take a look at the metal casing just above the spark plug lead it should be stamped onto the casing. You will see the model type and code numbers listed.

If you can’t find the model numbers be sure to remove and outer cover and check near the exhaust heat guard and all around the engine itself.

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

Once you find all the details you can check the exact engine using the identifier page at the Briggs And Stratton website.

Spark Plug

Before I do any work or servicing on a lawnmower I first remove the spark plug.  I always use NGK spark plugs and have so far not encountered one faulty one.

You can find all parts required for servicing here

I have serviced hundreds of Briggs And Stratton Lawnmowers using these spark plugs.

The correct spark plug for a Briggs And Stratton 35 Classic engine is NGK B2 -LM.

These spark plugs come with the correct gap specifications already set and be sure not to overtighten the spark plugs when re-fitting as you can accidentally close the gap as the piston get too close.

I like to fit the spark plug hand tight and then an 8th of a turn with a spark plug socket. I would advise re-fitting the spark plug as the final part of servicing for safety reasons.

The correct spark plug gap setting for a Briggs And Stratton Classic engine is 0.76mm (0.030 in)

Briggs And Stratton have a spark plug wrench with 19mm and 21mm ends for easy removal of two different size spark plugs.

The official part number for a Briggs And Stratton spark plug wrench is Briggs And Stratton 992356

Feel free to check out my Youtube video I made to accompany this article.

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Oil And Fuel

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.

Its a quick and clean way to remove old oil 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.

When it’s time to replenish the oil the correct oil is SAE 30 Oil and the Briggs And Stratton Classic Engine take 0.6 litres to re-fill.

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.

Air Filter

To remove the air filter on a Briggs And Stratton 35 Classic lawnmower engine only requires the removal of one screw.

Take a flathead screwdriver and remove the screw from the top of the air filter housing.

The thread on the screw is fairly long so be sure to unscrew it fully and pull the screw up and out of the air filter housing.

Lift off the air filter and turn it over. You can now remove the sponge air filter.

Often if a lawnmower has been tipped over this air filter can be black with oil. You can either replace the air filter or clean it off thoroughly in some old petrol/gas.

When refitting the air filter take a small amount of fresh oil and smear it very lightly on the air filter. This helps attract dust and particles and should help your air filter stay clean.

I regularly repair lawnmowers for profit. Please check out this playlist with over 90 videos on Briggs And Stratton repairs

Air filters are inexpensive to replace and I suggest replacing them whenever servicing.

The correct air filter for a Briggs And Stratton Classic Engine is Briggs And Stratton part number 698369.

Starter Recoil Rope And Handle

Removing the starter recoil gives you access to everything you need to carry out a service.

The design of the Briggs And Stratton 35 Classic is very simple and really easy to work on.

To remove the starter recoil assembly you will need to remove 3 bolts.

Take a 10mm socket or spanner and start with the bolt above the spark plug. There are two further bolts on the rear of the starter recoil one near the engine oil dipstick and one through the exhaust guard.

Remove these 3 bolts and place them in a magnetic parts tray.

Often the bolt that goes through the exhaust guard has a slightly wider head so it may be worth labelling or colour coding the 3 bolts.

Lift the starter recoil off the engine and set it aside. If the pull cord is attached to the lawnmower handle you should un-attach it now.

  • Note never cut the starter recoil rope from the handle. It will wind up the pull cord inside the recoil.

Take a look at the starter rope, if it looks frayed or damaged it should be replaced.

I buy 100-meter lengths of 3.5 mm pull cord rope. It’s not much more expensive than purchasing one single starter cord.

To replace the starter rope pull out the cord all the way against the tension of the recoil spring and clamp the recoil so it can’t move.

Here’s a video from my Youtube channel on how to replace a starter rope on a Briggs And Stratton 35 Classic Engine.

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Pull out the old starter cord and cut it off. Also, pull out the cord from the opposite end and remove the starter handle.

To measure the length of your new pull cord simply lie the old cord along the ground next to the new one. Be sure to leave a little extra on the new cord to allow you to tie a couple of knots.

Burn the end of the new pull cord to stop it fraying. It also helps push it through into the starter recoil. Align the new rope up with the recoil and push it through and tie a knot. Push the knot down into the recoil so it doesn’t obstruct anything.

  • Note Leave the clamp in position.

Now burn the opposite end of the pull cord rope and re-attach the pull cord handle. Release The clamp and slowly let the spring take up the tension and rewind the new starter rope.

The first time you attempt this procedure it can be a little awkward, however, if you are looking to repair lawnmowers regularly for profit like me then it’s something you will need to do.

I can do the Briggs And Stratton Classic pull cord in under 5 minutes partly thanks to the simple design, After a couple of attempts you will be able to do the same.

Brake Cable

The Briggs And Stratton 35 Classic engine uses a brake that sits against the flywheel. This brake needs to move far enough away from the flywheel to ensure easy starting.

With the starter recoil cover removed, we can now see and check the brake is working correctly.

Operate the safety lever on the handle of your lawnmower and you will see a brake, along with a kill switch move away from the flywheel.

If it doesn’t move away sufficiently take a look at the brake release cable and make sure it’s installed properly.

To remove a faulty brake release cable take some long nose pliers and squeeze the cable connector. You can now pull the cable back through the housing and replace it if necessary.

Kill Switch

The kill switch on a Briggs And Stratton 35 Classic lawnmower sits near the brake. If you can’t see it look for a small plastic cover that protects it.

It is on the back of the flywheel.

Remove the bolt and lift off the cover. You will now see a small switch with a small wire attached to it.

It’s essential that the kill switch operates correctly or you will either not get a spark or if the lawnmower does run it may not stop!

Clean the kill switch and operate the safety lever on the lawnmower handle once more.

There should be a disconnection of the kill switch whilst the safety handle is pulled and a connection once released.

Take a look at the metal tab that makes the connection and make sure it’s free from dirt or obstruction and that it connects properly.

The correct part for a Briggs And Stratton Kill Switch is Briggs And Stratton Part Number 692310.

For a detailed video on kill switches take a look at this from my youtube channel and be sure to subscribe.

Ignition Coil

The ignition coil should not need any adjusting during a service, however, I will include the information on how to set the ignition coil gap to the flywheel.

On either side of the ignition coil, you will find two small bolts, loosen them both but leave them in position.

Turn the flywheel to a position where the magnets on the flywheel do not grab the ignition coil.

Take a piece of card around the thickness of a playing card and place it between the ignition coil and the flywheel, next turn the flywheel to a position where the ignition coil is grabbed by the flywheel with the card in between.

Tighten the two bolts evenly and rotate the flywheel to remove the card. You should now have an even gap on both sides of the ignition coil in relation to the flywheel.

I have only ever had one ignition coil fail in the hundreds of lawnmower I’ve repaired for profit.

More commonly the problem is with a break in the wire that runs around the flywheel to the kill switch.

Spark Plug Lead

With the spark plug removed take a look at the connection inside the cable.

When you push this lead onto the spark plug you should feel a click if it’s connected properly. Occasionally the inner connection can become bent and damaged.

Governor Flap

The governor flap assembly is a plastic semi-circular flap that runs part way around the front of the flywheel. Make sure it moves freely and springs back against the governor springs.

There is no setting of the governor flap. It opens and closes against the flywheel when the engine is running to help maintain an even speed on all terrain.

Make sure it is free from obstruction.

Cooling Fins

One common question I’m asked is why does my lawnmower start and run for a few minutes then die. The answer is usually because it overheats.

Take the time to clean out all the cooling fins around the engine. If they are clogged the lawnmower will quickly overheat and cut out.

White Smoke Problems

If you have a lawnmower that pumps out white smoke, leave it running for at least 10 minutes to burn off all the oil that has been tipped into places it shouldn’t be.

The Briggs And Stratton 35 Classic Engine is particularly prone to white smoke problems after the engine has been tipped up or over.

Unfortunately, I don’t know of a more environmentally friendly way of removing the excess oil without running the engine. If it helps you could run the engine in 2-minute sections to reduce smoke.

Servicing The Carburettor

Servicing the carburettor on a Briggs And Stratton 35 Classic engine is fairly straightforward. The reason for this is it only takes the removal of two bolts to remove the entire carburettor and petrol tank.

This is why I always suggest this Briggs engine as a great starting point for anyone looking to start repairing lawnmowers for profit.

Check out my video on how to replace the diaphragm and gasket and service a Briggs and Stratton 35 Classic Carburettor here.

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Please note the DVD is no longer available for sale but you can watch it all for free here.


With all the fuel now extracted remove the petrol cap. This gives easy access to the 13mm bolt to the left-hand side of the carburettor.

Use an extended 13mm socket to remove this bolt.

Next, take a 10mm socket or spanner and remove the second smaller bolt towards the front of the lawnmower.

Refit the petrol cap and pull the petrol tank towards you. It will pull away from the lawnmower and is now only held on by one spring linkage.

Unhook the linkage and set aside the petrol tank and carburettor.

Clean any outer areas of the carburettor and petrol tank to avoid further problems when cleaning the inside of the carburettor.

Looking from above you will see 6 screws that sit around the carburettor. Remove these screws now and put them in a magnetic parts tray. All the screws are identical.

Pull the carburettor up from the petrol tank and be sure to not lose the small spring that sits on the underside of the carburettor.

The spring part number is Briggs And Stratton 691839

Remove the diaphragm and gasket from the underside of the carburettor.

The part number for a genuine Briggs And Stratton Diaphragm and gasket set is 795083 this number replaces the old part number of 495770. (same parts)

You can find all these genuine parts on the recommended products page:

The long pick up tube on the carburettor actually pulls off the carburettor but may require a little persuasion (part number 496046S).

Spray all the carburettor and tank with carburettor spray and blow everything out with compressed air.

Make sure everything is clean and dry including the long pick up tube. This tube has a filter. Make sure it’s clean and when you look through it you should see daylight through a small hole.

Here’s a video of a complete teardown of a Briggs And Stratton lawnmower engine.

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Push the pick up tube back into position. It will click loudly as it goes back on.

With everything clean and dry take a new diaphragm and gasket set and place it on the petrol tank.

The thinner diaphragm goes on first against the top of the gas tank and then the thicker gasket sits on top of that nearer the carburettor.

If you have a lawnmower that hunts and surges it’s because the thinner diaphragm has worn out and become wrinkled. This tiny part works in conjunction with the small spring to transfer the fuel.

Carefully replace the carburettor on the petrol tank making sure the spring sits evenly.

Look down from above to line up the diaphragm gasket and carburettor and refit and lightly tighten the 6 screws.

When everything is lined up correctly, tighten the screws fully working in a criss-cross pattern.

Take a look on the back of the carburettor there should be two seal washers, a black one and a white one. If you don’t see them look on the lawnmower inlet manifold itself. They may still be on there.

The white seal is actually a retainer (part number 697478).

The black seal is the inlet seal (part number 270344S).

If these parts are missing from the back of the carburettor then refit them onto the back of the carburettor. The black one goes in first with the white one sitting on the outer edge.

Offer the carburettor up to the lawnmower and re-connect the spring linkage. Make absolutely sure it goes all the way through the hole.

Next slide the carburettor back onto the lawnmower and re-insert the 2 original bolts we took off at the beginning.

Make sure all the springs and linkages move freely in a tug of war fashion and that the linkage is all the way through the hole.

Make sure the governor flap moves freely and the servicing of a Briggs And Stratton 35 Classic lawnmower carburettor is complete.

You can find genuine spares on the recommended products page including Briggs And Stratton diaphragm and gasket sets and most items discussed in this article.

Never use non-genuine parts. They don’t work well if at all particularly diaphragm and gasket sets.

The part number for a new genuine Briggs And Stratton 35 Classic Carburettor is  Briggs And Stratton 498809.

The carburettor is a plastic part that sits on a metal petrol tank, very occasionally they can lose shape so you may wish to replace the carburettor and the gas tank.

The part number for a petrol/gas tank for a Briggs And Stratton 35 Classic is 494406.

Head Gasket

To inspect the head gasket or replace it you will need to remove the control arm and the head of your Briggs And Stratton 35 Classic engine.

With the starter recoil removed you will see 8 bolts. Remove the exhaust guard first to allow full access then remove all 8 head bolts.

Pull the head of the engine away and inspect the head gasket. I always suggest replacing it at this point as sometimes removing it can cause damage.

It will be worth de-carbonising the head at this point.

Make sure the piston is at top dead centre to stop and carbon deposits and use whatever is at your disposal to clean off the carbon.

Fit a new head gasket and re-fit the 8 bolts tightening in a criss-cross manner.

The correct Briggs And Stratton part number for a 35 Classic Engine head gasket is part number 698717

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

Primer Bulb

While the air filter box is removed you should check and test the primer bulb.

Take a look from above the carburettor and push the primer bulb.

You should see fuel being pushed across. If you don’t see any fuel, I recommend checking the primer bulb for cracks and splits in the rubber.

Replace the primer bulb if necessary with a genuine part as aftermarket primer bulbs are poor quality and don’t last very long especially if you store your lawnmower outside or in cold conditions.

The correct part number for a genuine Briggs And Stratton Classic primer bulb is 694394


The Briggs And Stratton 35 Classic Engine does not have overhead valves (OHV) instead it is a flathead engine.

It’s not necessary to set the valves during the service but I thought it may be useful to include this information.

The valves and valve guides are designed to last a very long time without any adjustment.

You can replace the valves or grind them to get the correct clearance.

To do this procedure remove the exhaust and you will see what I refer to as a hidden door. Remove this door and you will see the valve stems and valve springs.

To remove the valve springs use a Briggs And Stratton Spring Compressor tool (part number Briggs And Stratton 19063) or visit the recommended products page.

You can get the correct valve clearances by grinding the valves, valve seats and valve stems.

The correct settings for the clearances are:

Inlet valve clearance 0.13 to 0.18 mm (0.005 to 0.007 in)

Exhaust valve clearance 0.13 to 0.23 mm (0.006 to 0.010 in)

Use a feeler gauge to measure the clearances.

This procedure should not be undertaken by anyone without a good mechanical background. I would recommend using your local lawnmower repair centre for this repair.

Governor Springs

One common mistake I often see is when someone has attempted to stretch or adjust the governor springs.

Governor springs sit between the primer bulb and the engine and when attached correctly do not require any adjustment. Make sure the springs move freely and are unobstructed.

Check out this article on how to replace the governor springs

Attempting to alter the governor springs will not help and hunting and surging problems you may have.

The only way to solve hunting and surging issues on a Briggs And Stratton Classic Engine is to replace the diaphragm and gasket and service the carburettor.

You can adjust the engine speed slightly by slightly shortening the longer of the two springs or bending the tab it attaches to.

Flywheel And Flywheel Keys

If you experiencing any kickback when starting a Briggs And Stratton 35 Classic Engine you should check the flywheel key at the top of the crankshaft.

To do this you will need to remove the flywheel itself.

The only correct way to do this is with a flywheel puller. Briggs And Stratton have a tool specifically designed for this procedure (Briggs And Stratton Part Number 19069)

Having a flywheel puller makes removing the flywheel a simple process. It is designed to screw in the top of the flywheel where the holes are pre-drilled and pull the flywheel up and off the engine. This little tool will save you a lot of time.

Intake Manifold

With the starter recoil removed you will also see the inlet manifold. It looks like a long tube that runs horizontally across the engine. It’s the part that the carburettor slides on and off. This Intake manifold also has a gasket that will be worth inspecting and replacing from time to time.

If the intake manifold gasket looks worn or old you should replace it with a new one.

There are 3 various intake manifold shapes used on the classic engines round, triangular and rectangular.

The round engine intake manifold Briggs And Stratton Part Number 699644

The triangular engine intake manifold Briggs And Stratton Part Number 792388

The rectangular engine intake manifold Briggs And Stratton Part Number 693446

Winter Storage Of A Briggs And Stratton 35 Classic

If you are planning to leave the fuel in your lawnmower for an extended period of time I suggest adding some fuel fit additive, it will help prevent fuel deterioration over long periods such as the winter months.

Briggs And Stratton offer fuel fit additive the part number is Briggs And Stratton 992380.

Final Thoughts

The Briggs And Stratton 35 classic engine is a fantastic engine to have on a lawnmower it’s also very simple to work on. Parts are easily sourced and I have linked to many of the above items on my recommended products page.

If you are looking to start your own business working from home I highly suggest starting with a Briggs And Classic Engine.

Many of the things you will learn whilst undertaking the repairs will be useful in the future. Most other lawnmower carburettors don’t use a diaphragm and gasket however the carburettors have more linkages and springs to attach.

What I really like is that you can remove the air filter and complete petrol tank and carburettor away from the engine with just 2 bolts and 1 screw.

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

If you are wanting to start repairing lawnmowers for profit then it will be worth reading my article

This is more advanced on a Honda lawnmower as the carburettor bolts through the air filter housing and also has a separate fuel line that needs to be clamped before removal of the carburettor.

There are plusses and minuses to both systems but for ease of access and inexpensive replacement parts, the Briggs And Stratton 35 Classic Engine wins hands down.

If you are still having problems starting your lawnmower check out my video here

You can subscribe to my channel here

One final thought would be to always use original parts. I have tried many aftermarket spares over the years and there is a great deal of difference between aftermarket and original parts.

All parts recommended on my recommended products page are genuine Briggs And Stratton spares.

This really is a great engine you can start learning how to repair lawnmowers for profit on and earn yourself some additional income.

Happy Mowing.













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