Briggs & Stratton : Dies when hot, backfires

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  #1  
Old 09-05-08, 02:52 PM
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Question Briggs & Stratton : Dies when hot, backfires

Hey guys....hope you can help as I am an extreme noob when it comes to small engines, riding lawn mowers, etc....but a friend just passed along to me a riding lawn mower that I would like to see if I could get fixed. We just purchased a house and I don't have the money currently for a new mower, so ... this is what I got.

First off, its a riding mower thats uglier than home made sin, but it runs fine until it gets hot. I believe its an MTG Mastercut, and when I flip the lid, this is the info on the engine:

Model: 286707
Type: 4025 01
Code: 0311114A

Its 12.5HP, B&S, 38" Cut and 7 speed trans

So, I haven't had a chance to even use it yet (raining..thank you Hannah) but would like to work on it while the rains here and hopefully be ready to go once its gone...anyway, as far as I know, from what the friend said (it was given to me, so I wasn't being sold anything) is that it starts right up, which it does, and that it will go about 10-15 min before it will start to stall and backfire. At that time, you have to let it cool and the process can be duplicated over and again.

I searched these forums and found a few things that look like contenders for the culprit...I saw one post where, the fuels running to lean, causing the carb or engine to get to hot, causing the fuel to ignite to early??

And the other potentially being a coil...now I will also say here that the person that gave me the lawn mower did say that had a mechanic friend look at it and he said he thought it was a coil as well.

So..anyway, there is my story...more than willing to gather any additional info and take pics, whatever...just hope to be able to get her right.

Anyway...thanks in advance for any help that comes my way.

 
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  #2  
Old 09-05-08, 05:24 PM
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it definately sounds like a coil. this is very easy to check. start it, let it get hot and die, then check fire. you can do this many ways, but the best way is to purchase a tester at the local auto parts store, an inline tester is the best. you can remove the plug wire, attach it to the tester, and attach the tester to the plug. this way you don't have to work on a hot engine. now if you still have fire when it dies, you may have a fuel delivery problem. you could have a gas cap that is not venting properly. to check this, simply remove the cap as it is dieing. if it picks back up, you have got it licked. or if it restarts faster, you know this is your problem. you could also have a sheared flywheel key over heating the engine. for this the flywheel must be removed in order to check the alignment key. i have also seen instances where there was trash in the fuel tank. some fuel tanks have filters built in, if this is the case, the trash can plug up the output on the tank while running, and drive you crazy! i would check these things first!
 
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Old 09-05-08, 06:37 PM
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Great!

Wow...thanks, Bill!

Lotsa good stuff there, and I will definitely attempt to test that tomorrow...is there a way to test without the inline tester? If not, how much do they cost, as money is a concern, but if I gotta...I gotta.

I will get back to ya one way or another on how it goes...if it IS the coil, do you know where I can find the part # for it, and do places like Home Depot or Lowes carry such parts, or would I need to go to a specialty shop?

Thanks again!
 
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Old 09-05-08, 07:06 PM
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The best way to check is with a spark tester, but you can check it many ways. You can remove the spark plug, but be careful it will be very HOT, plug the spark plug wire on it and ground the plug to the engine then crank the engine while looking to see if a spark jumps the gap on the plug. You can grab on to the end of the wire and crank the engine, if your eyes pop out and you smell burning hair then you know you have spark!!

Another thing to check is the fuel cap to make sure the vent is open.
 
  #5  
Old 09-06-08, 08:22 AM
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Originally Posted by 30yearTech View Post
The best way to check is with a spark tester, but you can check it many ways. You can remove the spark plug, but be careful it will be very HOT, plug the spark plug wire on it and ground the plug to the engine then crank the engine while looking to see if a spark jumps the gap on the plug. You can grab on to the end of the wire and crank the engine, if your eyes pop out and you smell burning hair then you know you have spark!!

Another thing to check is the fuel cap to make sure the vent is open.
Thanks 30YrTech...much appreciated. On my way to Lowes now to see if I can find one...don't suppose anyone can point me to the part# of the coil, or somewhere I can find it myself? Also, does Lowes / Home Depot, etc carry these parts?

Again, any advice is appreciated.
 
  #6  
Old 09-06-08, 10:55 AM
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492341 ARMATURE MAGNETO, this is the Briggs and Stratton part number for the ignition module. I don't think Home Depot or Lowes carries these parts. You will most likely need to find a Lawn mower shop or dealer in your area, or you can use the dealer locator on the Briggs website.

http://briggsandstratton.via.infonow.net/locator/

There are also numerous websites that sell parts, including Sears.
 
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Old 09-07-08, 01:32 PM
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Sorry for the delay...

Ok, I have an update, but not the one I think I wanted to bring...but here it is.

Ok, so I was able to mow my entire front yard (30 min-ish) without any problem from the mower yesterday, and even got partway into the backyard (another 15-20 min) before it did the mentioned backfire (and a little sputter) and died.

Now when it started to happen, I attempted to fight it from dying by lowering the throttle, which helped for a few seconds, and then trying to adjust the choke, which helped a little too, but it eventually still sputtered and died.

Now, (this is where I didn't get what I wanted) I didn't get to check whether I was still getting a spark, but I was able to turn the key off and back on and it started right back up.

Also, I think that if I were to have pulled the blade up and thrown it in neutral, it would have ran til it ran outta gas, but this is pure speculation on my part...

Now, all of this is pretty much irrelevant at this time, because while mowing in the backyard, somethings happened to the blade, because as soon as I attempt to lower it, I smell rubber burning. I am assuming that somethings happened to cause the blade to not spin, and what I'm smelling is the belt turning on the stuck pulley. I didn't hit anything while mowing, but there were a few times when it sounded like the blade was hitting the deck and I don't know why. Not sure if flex in the mower would do this when I was riding on uneven ground, but it did seem to happen in the same spot every time. Kinda weird....there wasn't any evidence of anything on the ground as I rode past where it happened.

Anyway...I am going to assume that this is probably something I need to take into a shop for, but if you guys happen to know any ideas..I'm open to trying them.

As always, your helps appreciated

Mike
 
  #8  
Old 09-07-08, 03:19 PM
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May have a spindle on the mower deck that has bad or worn out bearing and may be binding, You may also want to check the blades to be sure they are not bent and causing your problem. You should also check the condition of the mower deck drive belt as you may have a bad spot in it as well.
 
  #9  
Old 09-08-08, 10:31 AM
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Well...so far so good...

Okay...so here is the latest.

I checked under the mower last night, and where the (not sure the technical term for it) grass shoots out from under the mower, the outside part of it (the side closest to the front of the mower) was bent inwards, thus making the radius under inside the deck smaller, and the blade catching on it and unable to turn....so I got out the BFG unit, wacked it a few times to get it pulled out some, and hopped on and started her up and away it went. I mowed the entire backyard without a problem, didn't die, sputter or anything... although the twisting and flexing over the mower is definitely causing the deck to drag at times, which is causing the grass chute (or whatever) to get bent in....anyway, I guess its all working...just kinda worried if I should just go ahead and get a new mower, as this one is definitely old, and not sure how long it has left....and a guy near me is selling this mower, which is probably a good idea...I just don't wanna shell out the 450 for it...even tho I know its a heck of a bargain.

http://columbia.craigslist.org/grd/832500781.html

(Don't mean this as advertising, just asking if I should go ahead and bite the bullet and fork over the 450, or stick with what I have as it seems to be getting the job done.)
 
  #10  
Old 09-08-08, 05:38 PM
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That kinda looks like an HMS unit, do you have the model number of it??

The Toro's with this HMS setup had several issues in the drive system, so I would find out the model number and do some research on it before biting the bullit!
 
  #11  
Old 09-08-08, 05:51 PM
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If what you got is working, and the engine seems strong, keep it, and keep saving that money for a better/newer one. Unless the price of riders is really outrageous where you live, I would not call that a heck of a bargain. There were several others listed on that list at the same or lower price. Most people sell their riders cause they know fixit time is just around the corner. The guys here can help make sure the one you have keeps running until you are ready for a new one. A little tlc and maintenance really can go a long ways.
 
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