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LOL....

I have an older model Murray 36" riding lawnmower with a 12 HP Briggs "Power Built" vertical shaft in it.

So far I have replaced a new carb, spark plug, fuel filter and all lines. Simple fixes but no luck.

The rider operates fine when it is cold and first started up, and mows well. But once warmed up it goes to pot, runs intermittently going good for 15 or so seconds
then spurting and coughing and back firing for 5-10 seconds, then once again pulls and runs good for no more than a 15-20 second period, then once again spurting, coughing and back firing.
It keeps doing that unless you let it cool completely down, then recycles all the way through again, running good till warmed up and then spurting
and backfiring then running good and once more again farting through the carb.

I am hoping it is not anything internally broken, but since it is interment I am wondering if the problem is something else.
What is the timing system on this or can maybe the firing system/coil/armature electrical on this be going bad and thus backfiring then running good?

The consistent, without fail 15 seconds good, 5-10 seconds backfiring then back to good is what has got me wondering.
Seems to me if it were bad valves or something it would be continuously firing bad once warmed up.

Please keep this girl out of the scrap yard. Disabled 60 yr old here so I cannot afford to replace her.

thanks for the help in advance.
New member with sparse knowledge on this model rider and engine.

Drew

Also, while throwing advice in here, how do I set the adjustments on this single carb, only two adj. screws on here. See attachment please.

Thanks again.

My guess would be the ignition coil. No easy way to test this, either.

The two screws are idle speed and mixture. Idle speed is the one that contacts the throttle shaft. Pretty obvious how that one works. The other will have an "initial" setting, usually 1 1/2 to 2 turns out from closed. This will be good enough to get the engine running and once it's warmed up, you turn the screw out until the engine starts to run rough, then slowly turn in back in until it starts to surge or die, then back it out a quarter to half turn. Then adjust the idle screw to whatever you wish. If the engine was already running rough when you started it, skip the step about backing out the screw.

Look on the engine for MODEL, TYPE and CODE numbers and post them. That will help immensely.

cpurvis said:

My guess would be the ignition coil. No easy way to test this, either.

The two screws are idle speed and mixture. Idle speed is the one that contacts the throttle shaft. Pretty obvious how that one works. The other will have an "initial" setting, usually 1 1/2 to 2 turns out from closed. This will be good enough to get the engine running and once it's warmed up, you turn the screw out until the engine starts to run rough, then slowly turn in back in until it starts to surge or die, then back it out a quarter to half turn. Then adjust the idle screw to whatever you wish. If the engine was already running rough when you started it, skip the step about backing out the screw.

Look on the engine for MODEL, TYPE and CODE numbers and post them. That will help immensely.

Click to expand...

Thanks CPurvis:

i will check those tips out tomorrow and see what happens and then repost to let you know the outcome if any.

Get an inline spark tester ( red tube ones are the best ) and some starter fluid.
Put the tester on and start mowing.
When it plays up, look at the tester ( dark place will help ).
If the tester blinks or fails to blink in time with the engine spluttering then your coil is the problem.
In this case, remove the blower housing and pull the small wire off the coil.
Fire up the engine and watch the tester, problem goes away then you have a problem with the cut out wire shorting out ( or ignition switch shorting out ).
NOTE if this engine does not have a fuel shut off solenoid you can only stop it by replacing the small wire or pulling the spark plug lead.

bertsmobile1 said:

Get an inline spark tester ( red tube ones are the best ) and some starter fluid.
Put the tester on and start mowing.
When it plays up, look at the tester ( dark place will help ).
If the tester blinks or fails to blink in time with the engine spluttering then your coil is the problem.
In this case, remove the blower housing and pull the small wire off the coil.
Fire up the engine and watch the tester, problem goes away then you have a problem with the cut out wire shorting out ( or ignition switch shorting out ).
NOTE if this engine does not have a fuel shut off solenoid you can only stop it by replacing the small wire or pulling the spark plug lead.

Click to expand...

Thanks so much for the info...its a learning experience. Haven't gotten a chance to get out there and play with it after posting but plan to soon when the coil gets here.

Will be sure to post and let everyone know how it is going.

As a pre-thought consideration...where is a good place (website) source to look for running known good used 12-12.5 to 16 HP vertical Briggs engines at?
Not sure if I need to replace but wanted to compare price worthiness if repairs go that far.

Thanks again...

DjDrew said:

Thanks so much for the info...its a learning experience. Haven't gotten a chance to get out there and play with it after posting but plan to soon when the coil gets here.

Will be sure to post and let everyone know how it is going.

As a pre-thought consideration...where is a good place (website) source to look for running known good used 12-12.5 to 16 HP vertical Briggs engines at?
Not sure if I need to replace but wanted to compare price worthiness if repairs go that far.

Thanks again...

Click to expand...

Google mower breakers.
There is not much money in it so there are not many breakers / bone yards out there.
Labour costs make it a no brainer for repair shops and there are very few owners who bother when they can usually pick up perfectly good mowers at the local tip that require little more than a new belt or plug.

Tight valves will also act up like that. Check your valve adjustment.

Sorry for the delay. It has taken this long because the coil I bought new turned out to be defective DOA and I had to wait again for a new replacement to ship and get delivered. Put it on today, and it started and ran good, but idled terribly fast and got hot to quick so I had to shut it off and let it cool down. Now I think I am having problems with it either flooding or a carburetor adjustment and have to play with it for a bit. Having to charge the battery in between testing intervals so it is taking a while.

I was asked for model number and such so here that is.

Murray 12HP Power Built B&S vertical shaft 36" riding mower
model #: 284 707
type: 1026-E1
code #: 020123ZD

Ignition coil #: 591459 replaced aftermarket
carb #: 799728 replaced aftermarket

SO once I figure out what the problem is with it starting and idling I will get back with everyone. Thanks so much for the help from everyone.

DjDrew said:

Sorry for the delay. It has taken this long because the coil I bought new turned out to be defective DOA and I had to wait again for a new replacement to ship and get delivered. Put it on today, and it started and ran good, but idled terribly fast and got hot to quick so I had to shut it off and let it cool down. Now I think I am having problems with it either flooding or a carburetor adjustment and have to play with it for a bit. Having to charge the battery in between testing intervals so it is taking a while.

I was asked for model number and such so here that is.

Murray 12HP Power Built B&S vertical shaft 36" riding mower
model #: 284 707
type: 1026-E1
code #: 020123ZD

Ignition coil #: 591459 replaced aftermarket
carb #: 799728 replaced aftermarket

SO once I figure out what the problem is with it starting and idling I will get back with everyone. Thanks so much for the help from everyone.

Click to expand...

Start the mower then go around to the carb.
manually work the governor lever.
If you can slow the engine down to proper speeds then the governor is incorrectly adjusted or broken internally.

bertsmobile1 said:

Get an inline spark tester ( red tube ones are the best ) and some starter fluid.
Put the tester on and start mowing.
When it plays up, look at the tester ( dark place will help ).
If the tester blinks or fails to blink in time with the engine spluttering then your coil is the problem.
In this case, remove the blower housing and pull the small wire off the coil.
Fire up the engine and watch the tester, problem goes away then you have a problem with the cut out wire shorting out ( or ignition switch shorting out ).
NOTE if this engine does not have a fuel shut off solenoid you can only stop it by replacing the small wire or pulling the spark plug lead.

Click to expand...

Okay, choosing this post because it dealt wit the cut out wire.

Here is what has happened since I last wrote (next to this last bottom post by me)

I have been going round and round on this. After determining that the first coil I bought was supposedly bad (from TEK but maybe cheap Chinese aftermarket)
I then waited for the replacement. Once installing the replacement it fired up and seemed fine but I didn't even make it to a test run on the yard before it failed to start again.
So I switched back to the old coil that had been cutting out originally and it fired up but of course the same problem of sporadically cutting out when under a load .

So I did some swapping between old and new and replacement carbs and coils and still have not gotten it to fire up like it use to, so easily before all this and it would almost always fire right up. So I pulled the plug, it was new as of three weeks ago, and it seemed fouled a slight but with all the dead start tries and then running to fast and a bit hot so I cleaned it up and am going to put it in and try again>

Now why I referred to this cut out wire is this.

If I unhook the cut out wire, that completely eliminates any ignition switch or wiring problems right? I should be able to cross the two battery terminals under the seat, the ignition and starter terminals, not the ones on he battery itself, and it should fire right up correct? I had done it this way before, just using the terminals and crossing it over and it worked every time before this coil problem arose. But now it seems that it is just dead. I presume this second coil ran for a few minutes and then went DOA dead. I am putting the old coil on, going to test it and then get back to you all. But removing the coils cut out wire that leads to and connects to the ignition switch "off" wire, it should eliminate the switch and allow it to start correctly, right?

I have not yet gotten a spark tester and ran it what with all the way and in the order of re-occurring events after trying this new coil out.

Hope I am not turning this into a big confusing mess but this eliminating the cutout wire would of course tell me if I have ignition switch problems true? That is if it is agreed it SHOULD start.

Waiting for a reply folks, and thanks for your patience. I will at least learn procedures for diagnosing the ignition at least on these little 12HP Briggs when done.

bertsmobile1 said:

Start the mower then go around to the carb.
manually work the governor lever.
If you can slow the engine down to proper speeds then the governor is incorrectly adjusted or broken internally.

Click to expand...

Thanks for that tip, I checked and when putting the new carb back on, I had gotten the idle linkage stuck a bit between the breather housing and the idle shaft plate so it had stuck open and would not decelerate when I would raise the throttle rpm. I rerouted it and got it lose and it worked until it failed to start at all on the second try. refer to my last post above for updates since. Thank you for that tip though.

I had not heard anything at all back from my last post here for a while so I figured I would have to take a different frontal attack defense/offensive mentality to get anywhere with this problem. LOL

I found a good Craigslist ad and went that route and bought two riders all in one setting. the photos are included.

I bought the light grey MTD 12HP B&S 36" cut for $45 since it had swappable parts for the motor pretty much...

Then I got the Craftsman (green) 16.5HP OHV 42" cut rider. from the same man and considered it a good buy on both..

and I think it was a lucky find but will accept any opinion input from anyone.

What is the Craftsman worth on sale for a fair price?

After finding out that the Murray replacement coil was still bad again after the second coil which proved bad after two starts, I figured it was a bad batch from China and a bad company to do business with.

So now at least I will be able to pull the working coil off the MTD, and install it on the Murray and find out if that resolves my problem, then if it does simply buy a better quality coil from a reputable seller warehouse and have that cured.
Then I found that the MTD simply needed a battery and maybe a carb rebuilt later on, but in truth it had been in the guy's barn for three years. A bit of smoke when you first start it, and the famous idle surge B&S are famous for but that is all I found wrong with it.

I had tested the old coils on the Murray by cranking the engine with the Key on, and holding the spark plug wire with an insulated set of pliers against first the spark plug, then the grounded engine main shroud. No spark at all even after the second coil had started and run the engine just fine for two or three successful tries then went deader than a door nail after that and still won't fire a spark at all. Cheap Chineee crap they are tho.

The Craftsman green rider was in his barn too and shows it from the great condition it is in. The MTD was his son's, and the other Craftsman was his son-in-law's who had just upgraded to a new rider to replace this one. It needs a drive belt and a tuneup but both mowers cut smooth and clean and sound good when they run, especially the Craftsman.

SO guys if you would please, give me an idea what the Craftsman is worth IYHO a fair price please ... and of course any and all advisory input is welcomed. A fair price means one that isn't if it's you're buying offer low ball haha. Not even sure if I would sell it given I now have two riders plus a third Murray I have yet to fix. Just wondered if I got a good deal on the buys.

Thanks all for sticking with me on this and being patient throughout my lost phase of learning. haha

Drew

whoops, sorry...here are the photos.....

If you thought you got a good deal on it, that's all that matters.

That's the beauty of a free market transaction--you valued his mower more than your money; he valued your money more than his mower. Both parties got what they wanted.

Drew, you might get more responses if you post your questions regarding the motor in the Briggs and Stratton section in this forum. Wish I could help you. I just did my first resurrection a few weeks ago.

Thanks everyone for the abundant help. I finally gave up and replaced with an authentic Briggs coil, paid the extra and got it from a more reputable company.
Fixed my problems and ran lie it was new.
Thanks again for the help.

DjDrew said:

Thanks everyone for the abundant help. I finally gave up and replaced with an authentic Briggs coil, paid the extra and got it from a more reputable company.
Fixed my problems and ran lie it was new.
Thanks again for the help.

Click to expand...

Just so you, and those who might read this post at a latter date know.
The coil has a chip in it that controls the spark much like the old points used to.
There are several different chips used that cause the plug to fire at different times.
There are also modules with different length high tension leads
So if you see any coil that the vendor says will fit almost any engine they are talking through the wrong end of their body.
I use good quality after market modules from reputable suppliers and I have around 20ish Briggs ones.

Secondly the mark ups in China are very small so no factory can afford to toss anything in the scrap bin.
Thus all the ones that Kohler, Brigs , Honda , Kawakasi reject get sold on the secondary market and most find their way back to the retail market after passing through a 1/2 dozen hands.