What are the common reasons why lawn mowers won't start?

[Hipa Jeremy]

Carbs? Spark plugs? Fuel systems? Need more suggestions! Please!

 

[Rivets]

There are only three reasons all engines will not start. No spark, No fuel, No compression. Now if you are asking what are the causes for one of these conditions, then you must first find out which of these conditions is occurring. No spark could be any of the following; bad plug, bad coil, bad switch, shorted wiring, etc. No fuel could be any of the following; bad fuel, bad pump, air leak, dirty carb, etc. No compression could be any of the following; bad rings, bad valves, bad valve clearance, blown head gasket, etc. You must find out which reason is causing the problem and then diagnose which of the causes is creating the problem.

 

[StarTech]

There are only three reasons all engines will not start. No spark, No fuel, No compression. Now if you are asking what are the causes for one of these conditions, then you must first find out which of these conditions is occurring. No spark could be any of the following; bad plug, bad coil, bad switch, shorted wiring, etc. No fuel could be any of the following; bad fuel, bad pump, air leak, dirty carb, etc. No compression could be any of the following; bad rings, bad valves, bad valve clearance, blown head gasket, etc. You must find out which reason is causing the problem and then diagnose which of the causes is creating the problem.

Very much to the point.

And of us must have good working tools including the one between out ears. That along with knowledge we first start with non invasive tests and proceed down the path they lead us. As Rivet said you check spark first and that fuel is present. Just because a spark sparks outside the compression zone doesn't always means it is good that why you need to test with a good plug. Other tests start getting a little more involved but are necessary at times to get started down the right diagnostic pathway.

Unlike the 652R repair I currently reworking. First it comes in with a non-working deck along with other problems. Operator reported that he was having to jiggle wires to get it to work before it completely failed.

Well what I have found so far it some idiot tried bypassing the operator present system haphazardly. He had one grounded wire floating when I got to harness. Not even physically tried in, just stuck in the connector. And someone had already touch the loose wire to the voltage regulator. Well repaired the electric clutch wiring at the connector and removed the that extra ground wire. Off to see what else the idiot did. At the operator present switch I found a tip off a spray can and a piece of duct tape. Removed and check the switch which was good. From there I had to get the wiring schematic for 652R. (a couple hundred bucks for SM if I had gotten it from the dealer). With that in hand I found that a relay was removed. When replaced the electric system was restored to factory operation. Now when operator get off the QuikTrac it will stop if not parked as it should.

Now I got the order a new stator and voltage regulator as those are shorted out. Plus I might need to pull the heads for valve seals.(just extra work from normal wear and tear, not part of the original problem).

All this because some idiot didn't know what he, she, or it was doing. Just give us mechanics a bad name, especially us that work under shade trees during the hot summer months. Here it would have only been less than $2 in parts to fix the original problem along 15 minutes labor. Now it is $150 in parts alone just to straighten the deck problem. Hopeful the equipment owner will go back for his expenses caused by the idiot. I calling the tech an idiot for not using his head to start with and for not referring to the service manual.

 

[Bertrrr]

I always start with a little starting fluid in the intake- if it hits and tries to start- it's a fuel problem - if not, it's ignition then you know which path to go down.

 

[shadetree#1]

It's how you hold your mouth.

 

[hlw49]

There are only three reasons all engines will not start. No spark, No fuel, No compression. Now if you are asking what are the causes for one of these conditions, then you must first find out which of these conditions is occurring. No spark could be any of the following; bad plug, bad coil, bad switch, shorted wiring, etc. No fuel could be any of the following; bad fuel, bad pump, air leak, dirty carb, etc. No compression could be any of the following; bad rings, bad valves, bad valve clearance, blown head gasket, etc. You must find out which reason is causing the problem and then diagnose which of the causes is creating the problem.

You forgot one spark has to be at the right time.

 

[MowerBladeService]

start or turn over? start? see the other replies, turn over? safety switches and electrical connections.

 

[srwa]

There are 3 conditions which must be in place for any internal combustion engine to run........IE: fuel, spark, time...if those are "in" place any engine should run.

 

[g-man57]

I like to work on small engine 'stuff'. It's fun and rewarding to make then run again. If something turns over, has compression, but will not start, you can buy them dirt cheap. I fix them and give them away. The last one I worked on was a Weed Eater brand with a 4.5hp Tecumseh engine. It was the nicest 'trim' mower ever. So light - no problem working around stuff. I gave it to an 80 yo woman who insists on doing the trimming at her home. Her husband rides around on his big JD. LOL

Anyway, this mower ran great. But it was hard to start. Starting fluid worked, but I didn't want this woman to have to resort to that. I played with it a long time. It ran so good that I didn't think it was the carb. No leaks, no bumb in the idle... It did have a primer bulb. If I primed it many times I could get it to start - but it would run a few seconds and die again.

So I started it and kept pumping the bulb and it kept running. Then I pushed the bulb in and held it - still running. I bought some new rubber bulbs, replaced the old one and it started and ran perfectly since then.

The hole in that primer must have negated any choke I tried to use. When I pressed and held the button, the choke function was restored. Anyway, just and FYI

I see lots of posters mention fuel and spark. An engine needs air too. A clogged air filter will make things run poorly or not at all. This is especially true with a chain saw. They are tuned to run a peak levels and don't like lack of air. Take the filter off, if foam, wash it wilh soapy water, rinse/dry. For a chainsaw filter, blow it out with air. They have a very fine mesh and just shaking it or knocking on something isn't good enough.

 

[9snapper]

Carbs? Spark plugs? Fuel systems? Need more suggestions! Please!

Carbs? Spark plugs? Fuel systems? Need more suggestions! Please!

My guess would be that the choke is not set correctly, set the throttle lever in the start position and check that the choke is fully closed, if it isnt, adjust cable so is fully closed, youtube will probably have a video of how to do this