Lawnmower not starting

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My mower is a yard machine by MTD. It is a 21 inch cut push mower with a Briggs and Stratton 500 series 158 cc with 5.00 horsepower. It has not been starting lately. I don't know if it is the spark plug, needs new oil or the engine is flooded. Anybody with any lawnmower expertise would be great thanks.
 
Old oil would not cause a mower to not start. An engine needs 3 things to run: Fuel, spark, and compression. If you're missing any of those things, it won't run. Compression is most likely fine and your problem is almost certainly fuel or spark.

Testing for spark is easy. You can buy a cheap spark tester, or you can remove the spark plug, plug the wire onto it, and touch the base of the plug to the engine. Have someone crank the mower while you look at the plug. You should be able to see a spark when the engine turns over.

If you have spark, you have a fuel issue. Inspect the carburetor.
 
Primer bulb or "automatic choke" version of the carb?

The auto choke ones get a bad rep, although mine's still working fine. I find that if it's sat for a long time, filling the fuel tank and then tipping the mower up on two wheels with the carb side of the engine down does a pretty good job of priming it even without the primer bulb.
 
Originally Posted By: exranger06
Old oil would not cause a mower to not start. An engine needs 3 things to run: Fuel, spark, and compression. If you're missing any of those things, it won't run. Compression is most likely fine and your problem is almost certainly fuel or spark.

Testing for spark is easy. You can buy a cheap spark tester, or you can remove the spark plug, plug the wire onto it, and touch the base of the plug to the engine. Have someone crank the mower while you look at the plug. You should be able to see a spark when the engine turns over.

If you have spark, you have a fuel issue. Inspect the carburetor.


I don't think I can do much better than this, except to add that I would guess it has a spark and either the carb is clogged/plugged or the diaphragm is ripped or not sealing. The diaphragm is probably a 4 dollar part, the cleaning you can do on your own pretty easily. Modern Briggs are easy to work on and/or difficult to put back together incorrectly.
 
Spray in a shot of starter fluid without pushing primer bulb. If it pops when you pull the starter handle your spark is good. If not try changing the plug. HF sells some in-line spark testers for cheap.

Unless its real old it does not have points and condenser. I have not had ignition problems of recent vintage engines (no points) other than a plug. A plug is cheap, just change it rather than evaluate it.

How long since it last ran?
 
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How old is the lawn mower and when is the last time you changed the oil, filter or spark plug?

About every two years, I replace the spark plug, oil and filter in my lawn mower. The last mower lasted 16 years.

Sears and Home Depot sell a "tune up" kit for lawn mowers. The kit is based on the engine not the manufacturer of the lawn mower. The kit contains the oil, spark plug and filter for that engine. If you haven't done these maintenance items, I would start there.

The hardest part is draining the oil.

Good luck.
 
We had a lawnmower that would run / die sporadically and sometimes just wouldn't run. Had fuel, had spark.

Turns out the plastic "intake manifold" after the carburetor was broken. Sometimes it would seal, other times it wouldn't. Little bit of duct tape and it ran another year.
 
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I had a lawn mower with a brigs and stratton engine and a no start condition, good spark,clean carb.. I finally determined that its air filter was SO clogged it couldnt breath at all.. you may check that..
 
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@OP:

does your B&S mower looks like this (mine) (with a sidedraft carb, not like the older ones)?

http://i1167.photobucket.com/albums/q627/questbuster/Craftsman mower/IMG_0633Medium.jpg



Also: per other poster's comments: when was the last time the mower started, did it run well? Have you checked/replaced the air filter so far?

Lastly: just like all internal combustion engines: it takes air, fuel(mixed together) and spark to get an engine going. One has to perform all 3 checks to ensure that everything is in good order before moving on to the next stage of diagnosis.

Q.
 
Was this mower used all summer with no problems and all of a sudden won't start? Tell us the story.
 
That engine has the carburetor mounted on top of a metal gas tank with a diaphragm mounted between the carburetor and gas tank.

Usually, they just need a shot of gas/started fluid shot down the carburetor throat to get them running/primed again. If it starts for a few seconds and then dies, you know that you have spark. If it won't stay running, you will need to replace the diaphragm between the carburetor/gas tank and/or get the carburetor rebuilt.

There are tons of youtube videos showing you how to replace the diaphragm and rebuild or replace the carburetor if you have never done this before.
 
Regardless, it is still to our (as well as OP) interest to be able to first identify what kind/type of engine he/she has.

I know/aware of B&S mowers up to abound 6hp running the old pulsa-jet carb type:

http://www.compgoparts.com/TechnicalResources/BriggsCarburetors.asp

later, most of these pulsa-jet type of B&S engines was re-categorised as "quattro" or "classic" type until recently.

But I'm also aware (actually recently overhauled one for my dad, circa 1998) that B&S moved to side-draft carbs for 5hp B&S (it's a 21" sears craftsman mulcher/rear-bagger) similar to the original link included.

We need info to properly identify the engine type before diagnosis begins.

Q.
 
Originally Posted By: Quest
Regardless, it is still to our (as well as OP) interest to be able to first identify what kind/type of engine he/she has.

We need info to properly identify the engine type before diagnosis begins.


He already identified it as a 500 series 158cc. That is a modern engine, made in the last 5 or so years. It is not a quantum.

It looks like this:
70370.jpg

_briggs_carb_assembly.JPG



And here is an excellent video on how to work on these carburetors:
http://www.youtube.com/watch?v=ObEOfiBdSXk

The Briggs & Stratton part number for the diaphram is 795083, available for $2.49 on eBay.
http://www.ebay.com/itm/Diaphragm-Gasket...=item35cf518c72

The Briggs & Stratton part number for the carburetor should be (verify first) 798758, available on Amazon and Ebay for $28, should the carburetor need replaced.
http://www.amazon.com/Briggs-Stratton-79...s=798758+briggs

Close the thread. Excellence has been achieved. Applause....
 
Put a new spark plug in first and verify spark (Champion RJ19LM). Also, if the gas is old, I would drain and replace with fresh gas before you can verify a carburetor problem.
 
MillerBB, that's funny. the duck has kept mine going strong 3seasons now.
I would like to a float carb, but haven't got around to looking into it.

My experience has been have a clean and oiled air filer and a fresh plug on hand. these diaphragm carbs do there job but run rich and dirty.

ken
 
Geez. I didn't know they use PJ carbs on anything approaching 5 horsepower. Used to be those were limited to the 4-horse and below engines.

My 6-horse B&S engines all have gravity-fed float bowl type carbs that never give any problems.
 
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