How To Service A Tecumseh Lawnmower Engine- A Complete Guide

I’m going to show you my complete guide for servicing a Tecumseh lawnmower engine in this article, including how to service the carburettor and solve any hunting and surging issues you may have.

I have repaired thousands of lawnmowers for profit over the years including hundreds of Tecumseh engines.

These simple engines can easily be serviced in around an hour if you follow the instructions I’m about to share, In fact, In my opinion, the hardest part about servicing these engines is removing the parts (and fluids) in the correct order so let’s get started.

Many of the service parts you may require can be found at my recommended products page. There is a specific section for Tecumseh.

https://repairlawnmowersforprofit.com/recommended-products/

The Exact Process I Use

I always start any servicing by removing any old oil and fuel from a lawnmower. Don’t worry, I’ll cover all parts of the engine service, but there a few key steps to follow at the very beginning.

You can find lots more information and start repairing lawnmowers for profit by checking out my online training here https://repairlawnmowersforprofit.com/recommended-products/lawnmower-repair-training-products/

Remove All Oil And Fuel From The Lawnmower

Please do not skip this section because it will save you from making a massive error when re-building the lawnmower after servicing the carburettor.

With most of the lawnmower engines I service or repair, it only takes a few minutes to refit the carburettor and test the lawnmower once servicing is complete.

With a Tecumseh engine, you need to re-fit a lot more parts to be able to test the lawnmower and it’s very time-consuming.

With this in mind, I strongly recommend using an oil extractor to remove all the fuel and oil from the engine.

Using an oil extractor eliminates the need to tip the lawnmower up or over to remove the fluids. Tecumseh lawnmowers, like many others, really don’t appreciate being tipped up as it sends fuel and oil into areas of the engine it shouldn’t be.

Not only will you have a massive white smoke problem when the lawnmower restarts, but it may also stop you being able to pull over the lawnmower engine at all. ( I’ll explain why later)

If your lawnmower engine runs, then I suggest running it for a few minutes to warm up the oil before extracting.

You do not need to run the lawnmower out of petrol/gas as this can pull any dirt from the bottom of the petrol/gas tank into the carburettor and cause further problems.

Just use an oil extractor to remove the fuel and please dispose of it in an environmentally friendly way.

I use a Pela 6000 Oil Pump – Oil Extractor/Oil Extraction Kit. Oil Change Sump Pump! 6 litre

I have used this product many times. Here it is in action.

There are smaller alternatives that will do a great job including Silverline 104616 Oil and Fluid Extractor Pump, 4 L

The next part of the servicing requires tipping the lawnmower up to access the blade underneath. With all fluids now removed we can do this without causing further problems.

Remove The Spark Plug

At this point, before working on the underside of the lawnmower cutting deck, you should remove the spark plug completely and leave it removed until all other servicing is complete.

You can re-fit a new spark plug at the very end of the service.

The correct spark plug is
NGK Spark Plug Single Piece Pack for Stock Number 1147 or Copper Core Part No. B2-LM

Sharpen The Blade

With all the fluids removed and the spark plug safely out of harm’s way, we can now tip the lawnmower up to remove the cutting blade.

Tip the lawnmower with the exhaust side facing the ground and the carburettor pointing up in the air. I usually just lean it against the fence or wall to do this.

To remove a lawnmower blade you will first need to clean the blade bolt off with a wire brush. This will make sure you are less likely to round off the bolt if it’s really tight.

Next, take some WD-40 or any penetrating spray and spray the bolt and surrounding areas.

I used to remove blade bolts manually with a spanner or socket but many times I would spend hours attempting to remove stuck blade bolts. They are particularly hard to remove if a lawnmower blade is bent.

Eventually, I purchased a New Clarke CEW1000 Electric Impact Wrench 240v

This tool has saved me many hours (and smashed fingers) and in all honesty, I wish I’d purchased it sooner.

Here it is in action removing a bolt that I simply could not undo.

With the blade removed you can either sharpen it using a hand file or use a bench grinder. You could even take it to a local service centre and have it professionally sharpened and balanced, or fit a brand new blade if you prefer.

I use a bench grinder.

To sharpen a lawnmower blade I follow the natural angle of the blade on the grinder until I get a clean sharp edge.

This may all sound very simple but the angle of the blade provides backlift for the cut grass to be transferred to the grass box so do your best to get it right. Also if you are experiencing vibration problems with the lawnmower you should balance the blade.

You can purchase a special tool to help you do this or just put a nail on the wall and hang the blade on it to ensure it is evenly weighted at both ends.

Check out this Arnold 6011-X1-0195 Blade Sharpening and Balancing Kit for Lawnmower Blades

This is a handy tool to own if you are servicing multiple lawnmowers and selling them on for profit.

Check The Blade Adapter

The blade adapter is the part the blade bolts on to. Usually, there are two holes near the centre of a lawnmower blade where the blade sits neatly onto the adapter.

Make sure there are 2 pins on the blade adapter and the blade is set on these pins evenly before re-tightening the blade back on.

There are a few jobs to do before we refit the blade, including cleaning the underside of the cutting deck.

Clean The Underside Of The Cutting Deck

Most lawnmowers that end up in the scrapyard have perfectly running engines and rotten cutting decks.

This is because of the grass, particularly when wet or damp, sticking to the underside of the cutting deck.

If this grass isn’t removed, it eventually rots the cutting deck and holes start to appear. Take a wire brush and a scraper and remove any old grass from the underside of the cutting deck.

This will also increase airflow to help send grass clippings through the chute and into the grass bag. Your newly sharpened blade with the correct angle will also help!

Clean Out The Belt Guard And Check The Belt

Hopefully, by now you can see my reasoning for removing all the oil and fuel at the beginning!

There are lots of serviceable items to check and service underneath the lawnmower before we begin servicing the engine itself.

If your lawnmower has a self-drive you should now remove the belt guard cover and remove any grass and debris. You will be amazed at how much is in there.

At this point visually inspect the drive belt and also remove debris from around the transmission box which is usually located beneath the rear wheels.

The main cause for a self drive not working is because the belt is either obstructed by grass or has actually been dragged off and chopped to pieces by the blade!

With all these tasks complete, replace the belt guard and blade securely, making absolutely sure it’s sat on the blade adapter properly.

You can now place the lawnmower back on the ground evenly as you will be finished with the underside. Hopefully, you will have no fluids leaking out and everything is kept clean and tidy.

If you have any problems with the self-drive be sure to check out this article https://repairlawnmowersforprofit.com/lawnmower-self-drive-not-working-help-and-repair/

How To Remove A Tecumseh Lawnmower Starter Recoil

Servicing a Tecumseh Engine on a lawnmower has good and bad points.

I always like to remove the starter recoil and engine cover to give myself the best access and it makes it much easier to work on the engine

The bad point is it’s a little annoying and slightly time-consuming part of the process removing the carburettor because of the design on these small engines. For this reason I remove the starter recoil first.

The good news is when Tecumseh engines are serviced properly they pull over really easily and run well.

There is no quick way to remove the carburettor on this type of lawnmower if you want to have full access and service it properly.

The best way is to start by removing the starter recoil cover and the petrol tank.

We need to remove these parts to have full access to all the linkages and springs plus we can also check the flywheel key at the top of the lawnmower crankshaft.

Take a look at this video which shows you how to do it before I explain it in more detail.

Start by removing the bolts from the starter recoil cover and petrol tank.

With these bolts removed you will quickly find you still can’t remove the starter recoil cover as there are two bolts through the exhaust guard that also hold not only the exhaust guard on but in-turn the starter recoil.

This is why a Tecumseh lawnmower engine takes longer to service than most other brands such as Briggs And Stratton And Honda.

If you look at the bottom of the exhaust you will see two bolts through the exhaust guard that need to be removed. The easiest way to do this is with a screwdriver as the bolts often have screw heads.

If you can’t undo the two bolts with a screwdriver then take a socket and fit it over one of the bolts with your hand.

Next, push a socket extension bar through the exhaust guard and connect it into the socket. With everything in position, you can remove the bolts and take off the starter recoil cover.

The reason I mention fitting the socket first and pushing the extension through the exhaust guard is to minimise any damage to the guard as the socket may not fit through the guard but the extension will because is smaller. (see video)

How To Set A Tecumseh Ignition Coil

The ignition coil probably will not need any setting during a service, however, I will include the information on how to set a Tecumseh ignition coil gap to the flywheel for future reference.

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

Next, 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.

The correct gap is 0.37mm (0.015 inches) , personally, I just use an old playing card and have never had a problem!

Re-tighten the two bolts evenly and rotate the flywheel to remove the card. You should now have an even air 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 kill switch wire.

How To Replace A Lawnmower Pull Cord

To replace a lawnmower pull cord you will need to pull out the starter recoil all the way and clamp the inner recoil with a clamp.

Cut off the recoil rope but do not remove the clamp at this point.

Measure the length of the old rope and cut off a new one slightly longer to allow for tying two knots. (I usually buy 30 metres at once) it’s almost the same price as a single one.

You will want to burn the end of the new rope to stop it fraying, this makes it easier to push back through.

Push it back into the recoil, tie a knot and pull it tight.

Again, do not release the clamp.

Fit a new pull cord handle (or the old one) to the other end of the new pull cord rope.

Remove the clamp and slowly allow the spring to take up the new rope and rewind it. It’s actually a lot easier for me to show you.

Take a look at this video from my Youtube channel.

You can purchase a new pull cord here
Pull Starter Cord Rope 3.5mm x 3 Metres Lawnmower Hayter Briggs Honda Engine

Or, if you prefer in 30-metre lengths
Oregon 522852 Heavy Duty Professional Starter Rope

How To Remove A Tecumseh Air Filter

There are two different types of air filter systems on a Tecumseh lawnmower engine.

One is a long coffin shaped air filter that lies above the carburettor, the other is a more “sports style” and is much smaller that sits directly to the right of the carburettor.

The sports type air filter is removed by simply twisting the filter and pulling it off.

The longer coffin type filter will need removing via two screws on the right-hand side of the carburettor. You can then remove the filter and the filter box.

How To Remove A Tecumseh Lawnmower Exhaust

With the starter recoil removed the next job is to remove the exhaust

Make sure it’s not hot before doing this!

Unfortunately due to the design of these small engines to unbolt the carburettor we need to remove the exhaust to give easy access to the bolts that hold the carburettor in place

It’s very straight forward to remove the exhaust, just bend down the two metal tabs surrounding the exhaust bolts and remove the two bolts using a socket or spanner.

Make sure you don’t lose the exhaust gasket.

How To Service A Tecumseh Lawnmower Carburettor

Finally with the starter recoil cover and the exhaust removed you will be able to see the two bolts that connect the carburettor to the intake manifold on the lawnmower.

Before undoing the two bolts and removing the carburettor, I strongly advise taking some photos on of the linkage and spring set up.

If you have a lawnmower that is hunting and surging you be fairly sure it is a fuel starvation problem caused by a dirty carburettor. Check out this article on hunting and surging issues https://repairlawnmowersforprofit.com/petrol-lawnmower-hunting-and-surging/

Although it’s pretty simple it’s often easy to forget something or replace a part incorrectly from memory.

Clamp the fuel line and pull it off the carburettor. I usually place a bolt in the end also to avoid any spillage and then release the clamp.

There are two bolts holding the carburettor to the intake manifold, you should undo them now and unhook the linkages. Be sure to take plenty of photographs first.

With the carburettor removed, place it in a tin or clean container. Carefully undo the drain bolt from the bottom of the carburettor and allow any old fuel to drain out.

Be very careful with this bolt. It is incredibly easy to damage the thread and replacement parts are very expensive.

Remove the bowl from the carburettor and keep an eye on the gasket to make sure everything stays together.

Pull out the retaining pin (over the container) and remove the float and the needle. Take your time not to lose any parts, for reference a Tecumseh lawnmower carburettor does not have a spring near the needle, so don’t presume you’ve lost it!

Next, you will need to remove the emulsion tube that runs up through the centre of the carburettor.

Take an Allen key and push the tube down from the top. When this tube drops out it will have a small O ring attached to the bottom. If this looks damaged or worn in any way then replace it.

There is usually another O ring that stays inside the carburettor so inspect to check it’s still there. It doesn’t need to come out. Sometimes it falls out with the emulsion tube and sometimes it doesn’t.

Spray carburettor spray all around and through the carburettor and get in every hole you can find.

Next, take an airline or a can of compressed air and blow out the carburettor until it’s clean and dry. Make sure every tiny hole in the main jet is immaculately clean, also make sure the bowl itself is clean.

Push the emulsion tube back up inside the carburettor. This requires some care and attention not to lose the O ring. I usually use the back end of a drill bit to push everything back into place. Make sure the O ring looks perfect.

Refit the needle back onto the float bowl and drop back into position. Push the retaining pin back through and refit the bowl.

Make sure the float bowl gasket is seated properly and in good condition.

Replace the drain bolt through the bowl and retighten it to the main carburettor body.

I have filmed a video showing how to do this exact process.

Check For Leaks And Good Priming.

Do not skip this step. It is absolutely essential.

Taking apart a Tecumseh engine to service the carburettor takes a long time compared to many other engines I regularly work on.

For this reason, we need to make absolutely sure the carburettor has no leaks before re-installing.

Place the carburettor on a level surface and reconnect the fuel line. Allow some time for the fuel to fill up the carburettor and make sure there are no leaks anywhere.

Next, replace the two screws where the air filter attaches and push the primer bulb.

Look inside the carburettor and make sure that when the primer bulb is pushed you can actually see fuel being pushed out.

Note. The primer bulb will not work without the air filter screws in position.

Although this may seem a little ridiculous to you I promise it’s true. Make sure the screws are in to test the primer bulb!

When you are satisfied you have no leakage and the primer bulb is working correctly, disconnect the fuel line, tip the carburettor over and allow any fuel to flow out. Do not drain it from the drain plug after doing the previous checks.

Replace The Head Gasket

Although not essential I usually replace the head gasket during a full service. They are inexpensive and it only takes a few minutes to do. It is worth considering doing at this point with many other parts removed.

Simply remove the bolts from the head of the lawnmower, turn the flywheel manually to make the piston come to the top. This stops any dirt entering.

Scrape off the old gasket from the engine head and from the engine itself. Order a new gasket (see recommended parts on this site) and replace the gasket.

Retighten the head back on working in a cross pattern to tighten the bolts.

I have repaired many lawnmowers where the head gasket needs replacing. It’s amazing how simple it actually is and can solve many problems of poor running.

Refit All The Parts

Without going through every step I will offer some information on how I go about re-fitting all the parts.

I find the easiest way to do this is to refit the linkages from the carburettor to the governor arm first. It is impossible to fit them later.

Fit both linkages from the carburettor to the governor arm, next take the inlet manifold that isn’t attached to the engine at this point and bolt the carburettor to it.

Now fit the inlet manifold back onto the lawnmower.

Doing it this way you have all the parts in moveable positions and it’s much easier.

Once the inlet manifold is connected to the engine make sure all springs and linkages move freely and are in the correct place (refer to your photos!)

Re-bolt the exhaust and refit the air filter.

Next, replace the outer shroud and recoil starter assembly. You can now place the petrol tank back onto the holding fittings at the back of the engine cover and re-connect the fuel line to the carburettor, once again checking for leaks.

This process takes a long time and a good amount of patience. Sometimes you may need a handy helper!

Take your time and make sure all the gaskets are evenly lined up as you go.

Fit A New Spark Plug

With all servicing complete the spark plug can now be re-fitted.

Before fitting a new spark plug pull the engine over a few times to make sure it is not locked.

This can happen if you leave the spark plug in and oil ends up near the piston when the lawnmower is tipped up.

Fit a new NGK Spark plug. Find one here NGK Spark Plug Single Piece Pack for Stock Number 1147 or Copper Core Part No. B2-LM

Technical Specifications For Tecumseh 3.5hp 35 4-Stroke Engines

Spark Plug Gap 0.8mm (0.032 inch) NGK B2 Lm Spark Plug is Recommended

NGK Spark Plug Single Piece Pack for Stock Number 1147 or Copper Core Part No. B2-LM

Ignition Coil to Flywheel air gap 0.37mm (0.015 inch) I use a playing card.

Valve Clearance Inlet and Exhaust 0.25mm (0.010 inch)

Piston Ring Gap 0.18 t0 0.43mm (0.007 to 0.017 inches)

Oil SAE 30 Lawnmower oil is recommended.

Don’t forget you can find many service parts here https://repairlawnmowersforprofit.com/recommended-products/

Final Thoughts

As stated in the opening paragraphs, Tecumseh lawnmower engines are pretty time consuming and can be frustrating to work on, however, there are many makes and models of lawnmowers that use these small engines worldwide.

I regularly repair Tecumseh engines for profit and I would have missed out on making some very good sales if I hadn’t taken the time to learn the servicing.

This isn’t the ideal machine to learn initial repairs on.

I would always pick a Briggs And Stratton 35 classic engine to start with.

I explain why in this article and there are full details on how to service them here https://repairlawnmowersforprofit.com/how-to-service-a-briggs-and-stratton-35-classic-lawnmower-engine/

One tip I will share with you is this. There is a massive shortage of second-hand spares for Tecumseh lawnmower engines on eBay. If you don’t want to do the repairs you could simply strip all the parts off these engines and sell them for profit.

I hope this article helps anyone looking for service advice on Tecumseh lawnmower engines, not the easiest to work on but certainly pull over easily and run nicely when serviced.

Be sure to check out the recommended parts store.https://repairlawnmowersforprofit.com/recommended-products/

Be sure to check out my youtube channel for more help and advice https://www.youtube.com/c/MowerMan

Happy Mowing