Lawn Mower Backfire /now Won't Start

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  #1  
Old 06-14-03, 07:38 PM
LAWNGIRL
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Lawn Mower Backfire /now Won't Start

My lawnmower backfired as I was shutting it off and now it will not start. It acts as if it may start but not strong enough. what happened? What should I check first?
 
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  #2  
Old 06-14-03, 11:50 PM
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Hello LAWNGIRL!

Is this a push mower, or rider? What engine is on it? (brand, horsepower, model)? Do you have spark at the plug?
 
  #3  
Old 06-15-03, 05:10 PM
LAWNGIRL
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It is a lawn boy commercial push mower and I am getting spark. It tries to start but is too weak and eventually quits. I'm not sure of the HP of the mower.
 
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Old 06-15-03, 07:40 PM
4stroke
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Timing?? Something Else??

It's not clear whether you're working with a two or four stroke engine.
Lawnboy seems to have hung on to the 2 stroke engine longer than most other mower manufacturers.
Let's assume you have a four stroke engine.
Backfire could mean an intake valve sticking open. Pull the head, roll the engine over and determine if the valves open and close properly.
If your engine uses breaker point ignition your points may have fallen out of adjustment or become weak or contaminated. Check to see that they are properly seated, open and close correctly and that the gap is proplerly set.
Did you hit something hard with the mower blade the last time you used the mower.
If so, it's possible that you sheared or partially sheared the flywheel key. This will cause backfire, hard starting, rough and low power running and/or no runningat all.
Pull the shroud and check to make sure the flywheel key is properly aligned and
not sheared.
If this is a magneto fired ignition, remove the shroud and make certain that there is a proper clearance between the flywheel and the coil pick ups. You can check to see if it's magneto fired by running the edge of a steel shaft screwdrive along the edge of the flywheel throughout its circumferance. If the flywheel attracts the screwdriver (magnetic attraction) it's magento fired. Clean the edges of the flywheel of any debris and make sure nothing interferes with the clearance between the coil pickups and the enge of the flywheel as the flywheel turns.
Good luck lawngirl.....
 
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Old 06-15-03, 10:01 PM
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4stroke has some good advice. I would also just change the plug...it could be bad. Another possibility is that the engine is flooding, due to a carb problem, or there could be water in the carb.
 
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Old 06-16-03, 04:09 PM
LAWNGIRL
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This is a two-cycle engine. I changed the spark plug and still doing same but seems to have a little more power but won't keep running.
 
  #7  
Old 06-17-03, 07:14 PM
4stroke
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Checking Some Simple Stuff First

As I recall, Lawnboy mower service manuals speak to the importance of ensuring that the exhaust ports remain clean. Clogged exhaust ports can produce loss of power, stalling, etc.
To get to the exhaust ports, you've first got to remove the muffler.
The Lawnboy mowers I've worked on have a muffler installed on the underside of the mower deck housing. Accessing the muffler requires removing the cutting blade. If you're not familiar with the correct safety procedures for removing the blade let a professional do the job.
Exhaust ports can be cleaned using a piece of hardwood dowel or similar tool, but we have to be careful not to allow pieces of the carbon pieces that are cleaned away to get into the engine as that could cause internal engine damage. One more thing about your ignition system settings.
The Lawnboy mowers with breaker point ignition use a spark plug gap of .025; solid state ignition plugs are set at .035. Make certain you're
using the correct gap on your plug.
While we're on the subject of ignition systems,(spark timing and duration)your breaker points (if you have them)are situation beneath the flywheel. Set the points at .020. The air gap between the flywheel and the coil should be set at .010. If you have a solid state ignition (instead of breaker points)the only adjustment will be the air gap (.010) between the flywheel and the coil.
On the air/fuel side of the coin, check to make sure that the throttle disc isn't jamming in the intake - it should move freely as you manipulate the throttle control.
Of course, you're using fresh fuel with the proper fuel/oil mix....
"Fresh fuel" means it isn't more than 30 days old.
Another thing I've learned over the years - never trust a working
ignition system.
I have had small engines drive me crazy when they'd start and run fine
for a while then stop for no good reason. Disassembly and checking of
ignition parts revealed that all parts checked good. Only when I replaced
a part with an "out of the box" new part did I determine that the ignition
coil or ignition module was breaking down as it warmed up. Frustrating to
say the least.
 
  #8  
Old 06-18-03, 07:05 AM
LAWNGIRL
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How do you get the flywheel off? I took the cover off and the nut at the top but now don't know how to get it off without breaking it. It says it requires 30lb torque...Thank you for all your help! I will also check the gap on the spark plug cause I did just take it from the box and assumed it was right.
 
  #9  
Old 06-18-03, 01:20 PM
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You will need a puller. If you don't have one you can rent one from auto zone.
 
  #10  
Old 06-19-03, 08:24 AM
4stroke
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Renting Your Tools

When you go to rent your tools (Auto Zone or elsewhere) make sure they understand that you're pulling a flywheel from a small engine. Some of the companies that rent tools hire folks that know less about your intended tasks than you do.
One more thing....
The "30 pounds torque" refers to the torque you will apply to the flywheel retaining nut when you put the engine back together. You'll need a torque wrench to do that. Make sure the person who rents,loans, or otherwise provides the torque wrench knows how to use it properly and knows how to demonstrate it's use....
 
  #11  
Old 03-14-09, 06:52 AM
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I have a murray lawn mower 4.0 hp engine quattro it wants to start but it sounds like a car is sputtering. I checked the spark plug,the oil, the gas its fine. I mean it started just fine then suddenly it stops.

ps. I had this thing for a long time it does fine
 
  #12  
Old 03-14-09, 07:01 AM
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zebraman;
Start a new post, it is at the top of the forum labeled "New Thread", the one you are hook on to is about 6 years old, also post the engine model and type numbers and we will get you taken care of. Have a good one. Geo
 
  #13  
Old 03-14-09, 11:49 AM
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no title

yeah well sorry just trying to get help but no someone has to yell at me. I dont see where you post new threads thankyou
 
  #14  
Old 03-14-09, 11:57 AM
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Not yelling..just informing...some folks won't go back to a thread they may already have marked as read/resolved.

Just go in to the main part of the topic..in the box at the top..small font. You'll see a "new thread" button above the older posts and announcements.

Don't forget the model and engine info if you can get it..otherwise its all just generic advice.
 
  #15  
Old 03-14-09, 03:41 PM
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zebraman;
Sorry if it sounded like I was being an a** , just trying to get you help as quick as possible. Have a good one. Geo
 
  #16  
Old 03-14-09, 09:02 PM
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I don't see anyone yelling. Geogrubb is a helpful member of this forum and would be glad to help you, but the proper way to ask a question in a forum is to start a new thread, not hijack someone else's. It's kind of hard to keep track of one persons problem when it's mixed up with some other person's problem. Accusing folks of yelling at you won't inspire them to help very much. Consider researching forum etiquette.

As for your mower, have you checked the air filter? Replaced the spark plug? What model engine do you have?
 
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