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Hi,
I have a lawn boy mower (5236 d-400 series) that is giving me problems to no end. It has problem starting (even after priming) and when it finally starts, it has very low power. My lawn has very short grass and the moment I push the mower there it just sputters and then dies. It's easier to start when hot but the low power problem still persists.
The plug is in good working condition, the ignition coil is new, and so are the seals. The only thing I am not sure about is the carburetor and governor.

Changing the lever from normal to heavy doesn't seem to affect the power in any way.

I had the carburetor cleaned some time back but seeing that I have been using it without the air filter, it may have took some dirt in. I tried to use a sponge in place of the air filter (which got lost) but the power got so low that the mower went off. I guess there wasn't sufficient air flow. I therefore had to do away with the sponge altogether.

Any help is appreciated.

Ok where to start. Wait I know. The carb is DIRTY. you can not run a low to the ground lawn mower without an air filter. Clean that carb the find a way to get an air filter on it. I have seen them zip tied on. Carb cleaner around the governor. It needs to move with out restriction.

I had this same problem once with an F series model. I took off the muffler to check the exhaust port for excessive carbon, but the root problem turned out to be that the muffler was plugged up with chunks of carbon--cleaned it out and it ran like new.

By the way, running your Lawn Boy without an air filter will severely shorten the engine life, but you probably know that.

As above, you need to run with that mower WITH an air filter. If you can't get to a dealer, you can just go to Amazon.com and key in "Air Filter for model #" and off you go. Or you can go with any of the numerous parts dealers online, but I like Amazon because you can choose from many offers on one item and get it for the least amount delivered. I have ordered air filters, blades, coils and other parts no problem. If you get into dicey parts like a spring for the governor, you may have to go to a place like Partstree.com. A new air filter will probably be well under 10 bucks delivered. WELL WORTH IT!


OK, so you don't run that mower any more without the air filter except in a garage to tweak the carb or clean it out with carb cleaner. That's the first thing I'd do. Give it a good spray with carb cleaner in the air filter intake port, and into the fuel inlet after you take off the fuel line. Some models have a tiny screen in that fuel line inlet that you can pull out and spray with carb cleaner. Then I'd clean all of the outside of the carb with carb cleaner. Then I'd make sure the Governor is pivoting easily. if not, spray around the pivot point and then use penetrating oil to make sure it's free to swivel when it needs to. Do not break the spring or you will be in a world of trouble until you replace the spring. Seeing you have run it without air filter you may have to take that carb apart for a good cleaning or rebuild, but I'd try spraying it with Carb Cleaner first. Inside and out. With some luck you will be OK with this method and not have to remove the carb.

Take off the muffler and check for carbon. Clean the muffler well. Look at the exhaust ports and make sure they are clean as a whistle. If not clean them out carefully making sure not to knock carbon into the chamber. Make sure your fuel vent on the gas cap is clear and you are not creating a vacuum when you run the engine. Check the spark. Make sure that new coil is putting out good spark. Pull the plug, ground it against the engine and attache the plug wire to it and give the starter a pull when in a dim or dark environment like a garage with the lights out. Is the spark good? I have seen new coils fail withing weeks of installation. It's not unheard of. I've also seen brand new spark plugs fail out of the box. Not unheard of either.

I assume you are using fresh gas less than a few months old, yes? And that your mixture is within standards. I've been running 40:1 synthetic lately and I have had no issues whatsoever. In fact, no more carbon in ports and muffler.

If I had a 20 dollar bill for every time my LB lost power due to one of the above issues, I'd be able to buy a new mower with the proceeds!

Good luck. I'm sure you will find the issue. These engines are not complicated. There are usually two or three simple things you can do to cure what you are experiencing.

I wanted to add something.

I've been working on lawnmowers and motorcycles for over 30 years now. Ignition coil (magneto) issues can very often mimic fuel starvation or carb/fuel issues. Often these are confusing to the new mechanic. I had a 95 Triumph that you would bet the ranch had a fuel delivery problem. It sputtered, ran rough, surged, and acted like you had hardly any fuel. Even fooled a 20 year Triumph technician whom replaced the vacuum system, fuel lines, petcock and tuned the carbs. No joy. The actual problem? Bad coil. Finally replaced the failing coil and bike ran like a top.

When coils are starting to fail, they often work sporadically. You may start, but then run rough, or bog down under load or stall out. It's not ALWAYS the coil going bad, but you can't rule the possibility out. It is absolutely something you should check, especially on LawnBoys where it is well know that coils have issues of failure more often then not.

There is a home remedy that I have tried on failing coils. You can try and "BAKE" them in a preheated oven at about 185 degrees for 30 minutes to revive them. Evidently, sometimes this takes out moisture and can possibly breathe new life into a failing coil. Personally, for 20 bucks on Amazon, I replace them.

Again, it is not always a failing or bad ignition coil, but you can't rule it out.

Thanks for all your replies and valuable input. I will be tearing the carb down this weekend as well as checking on the coil, spark plug, governor and exhaust ports. Hope by the time I am finished with them it will be running like new.
By the way, how do I ensure that the governor is set up correctly?

To check the governor components on the D and C series lawnboy motors the flywheel has to be removed. The governor has parts that wear (weights and collar) and can cause the motor to not run at the proper rpm. I would try the possibilities that everyone else has suggested before looking at the governor. Good luck and keep us posted!

Another thing that hasn't been mentioned is just plain old "low compression" from a well used mower engine. You got to have decent compression to get power. Have you run a compression test?

Yeah, that's a good point. It's usually very rare that it is a compression problem, but it can happen.

So many issues go back to either Carb or Ignition that Compression and Exhaust are frequently overlooked on our beloved LawnBoys.

I have a drill set-up with a drive for the starting bolt head. If I have sufficient fuel and compression but do not even get a "sputter' when I have my drill hooked up to turn the crank, then I'm pretty sure it's a CDI problem with the ignition, or the spark or the wire or something in the ignition chain. There have been times when it appears I have a decent spark, yet I can't even get a sputter from the mower no matter what, even with quick start sprayed into the carb. Putting on a new CDI/Plug will either cure the issue or you have to widen the search.

You should not overlook the exhaust ports and muffler, making sure they are clean. You don't want to bust your gut working on everything else in the mower and overlook the exhaust. I know it can be a dirty job, but it's worth it. If you've got a LB where the muffler is below deck, it also gives you an excuse to sharpen and balance the blade.

I've said this before, but if I had 20 bucks for every time I thought I had a carb or fuel delivery issue when it really was an ignition issue, I'd be able to buy a brand new mower by now.

Hi guys,
So I spent a better part of the weekend tearing the mower down. I have attached the pictures of the exhaust port and the governor. From my observation, the 3 holes in the exhaust port were clear. However, I did observe some oil deposits on one side of the exhaust port (NOT the side with the 3 holes). I don't know what this could possibly signify or whether the deposits were formed before I replaced the rings and seals (about 3 months ago).

Also, a quick look on the piston (through the exhaust ports) showed that it was a bit scored (kinda like scratched). Could this lead to starting problems and low power?

For the governor, I still don't understand much about how it should be set up properly. All the same, I did observe that tugging/pulling on the spring that is attached to the "normal/heavy" lever did not seem to make much/any difference on the yellowish thing that is attached to one arm of the governor.

I think the coil and spark are working well since I got a spark when I grounded the spark plug and gave the starter a pull.

I haven't managed to clean the carb yet as I don't have the carb cleaner and my Mech said he would be available over the coming weekend.

That is all I have managed to do at the moment. If there is anything you find from my observations or anything else you would like me to do, kindly let me know.

Almost forgot to add: The compression seems to be okay as the pulley rebounds when I run the compression test. However, I just noticed that the pulley seems to be brushing against the governor when I move it with my hands. Is it possible/advisable to run a mower without the governor in place as it seems to be hindering the free movement of the pulley?

Thanks,
Moses.

It looks like one of the flyweight lugs (on the governor) has jumped out of its slot. The governor assembly is supposed to touch the underside of the flywheel when the mower is not running. As the motor runs it is pushed down. The exhaust ports look OK to me. The kind of cast aluminum muffler on your model seldom gets plugged up, it will be very obvious if it is. A coating of carbon on the inside of the muffler does no harm. A motor that old can certainly be low in compression. A new set of rings is relatively inexpensive. You should make sure the governor assembly can push down on the crankshaft easily and in doing so moves the throttle butterfly lever on the carb. This all needs to work smoothly.

Guys,
I found someone else to help me clean the carb. After cleaning it, the mower seems to start well without any problems. However, it still struggles when I get to the grass. Do you think a new set of rings could cure the problem? Also, is there a way to know which rings to buy without removing the piston and reading the numbers?

Thanks!

rev20 said:

Guys,
I found someone else to help me clean the carb. After cleaning it, the mower seems to start well without any problems. However, it still struggles when I get to the grass. Do you think a new set of rings could cure the problem? Also, is there a way to know which rings to buy without removing the piston and reading the numbers?

Thanks!

Click to expand...

Possibly but not probably in my opinion. Did you do a compression test, or can you? I'd only suspect rings if you had measured poor compression. A more common cause of low power (assuming you are confident you tackled Governor, muffler/exhaust ports and have good Carb and Spark going) is the bottom crankcase seal. If this seal is leaking it will rob you of power. Between lower crank seal, governor, carb and spark those would be my first hits on loss of power. Lastly would be piston rings. However, IF they are worn and IF you are losing compression because of them, then this could possibly be a suspect of your issue on power loss.

I've had loss of power issues due to magneto/spark issues, carb, governor and crank seal. I've had start issues because of the same plus Reed valve. I've not yet had to replace the piston rings, but it's probably on the horizon at some point as I'm not parting with my LawnBoy.

bt3 said:

Possibly but not probably in my opinion. Did you do a compression test, or can you? I'd only suspect rings if you had measured poor compression. A more common cause of low power (assuming you are confident you tackled Governor, muffler/exhaust ports and have good Carb and Spark going) is the bottom crankcase seal. If this seal is leaking it will rob you of power. Between lower crank seal, governor, carb and spark those would be my first hits on loss of power. Lastly would be piston rings. However, IF they are worn and IF you are losing compression because of them, then this could possibly be a suspect of your issue on power loss
I've had loss of power issues due to magneto/spark issues, carb, governor and crank seal. I've had start issues because of the same plus Reed valve. I've not yet had to replace the piston rings, but it's probably on the horizon at some point as I'm not parting with my LawnBoy.

Click to expand...

I did the compression test by pushing the flywheel and then observing if there was a rebound. When I got one, i concluded that there was compression. Is there any way to know if the seals are the problem or a better way to do the compression test? Also, is the presence of oily substance on one side of the muffler a sign that the seal is leaking?

rev20 said:

Guys,
I found someone else to help me clean the carb. After cleaning it, the mower seems to start well without any problems. However, it still struggles when I get to the grass. Do you think a new set of rings could cure the problem? Also, is there a way to know which rings to buy without removing the piston and reading the numbers?

Thanks!

Click to expand...

You don't need specific numbers to order rings for late model "D" engines. Here is a link:

Piston Rings Replaces Lawn-Boy: 678422

The governor part under the flywheel key looks a little mangled to me.

I had the same d motor did the same thing you described did all the things mentioned in the posts.If you have good compression check the needle and seat in the carb.yeah thats what it was after hours of tinkering around.but unfortunately you have to rule out all possibilities.

beg said:

I had the same d motor did the same thing you described did all the things mentioned in the posts.If you have good compression check the needle and seat in the carb.yeah thats what it was after hours of tinkering around.but unfortunately you have to rule out all possibilities.

Click to expand...

May be worth replacing if you can get a carb kit where you live or online.