Briggs & Stratton 42A777-1270-01 Not Starting

Rick_ILMay 3, 2014

I have a Briggs & Stratton 42A777-1270-01 on a Lawn Man lawn tractor. I received it used, as a gift and spent the winter cleaning it up and giving it a complete overhaul.

To date I have replaced:
1) Starter
2) Start Solenoid
3) Ignition Switch
4) Magneto
5) Battery
6) Carburetor overhaul kit
7) Plugs

After the overhaul I could turn it over but not start it. After reading a pile of forums on this and other sites I came to the conclusion that the magneto (purchased straight from B&S was faulty). I purchased a second one and after installing (yes I set the gap) it started up straight away and ran better than it has since I received it...for about an hour. I had to run it at partial choke but aside from that it seemed to be performing well. During that run (under load) it throttled back momentarily but came back up without me adjusting anything. Suddenly, on flat ground, it shut off like I had turned off the switch.

Now it will not start. It is getting plenty of gas but I did notice that there wasn't much charge on the battery as I could only crank it a few times before the battery dropped. The original owner used to have a problem with it stopping when hot (needing cool down to run again) but it is now hours after and I still can't get it to fire up.

Is it possible to short out (damage) the magneto? It seems rather suspect that the first replacement and then this one may seem faulty.

Any ideas?

Rick in Illinois

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Charge the battery.
A slow cranking engine is hard to start. Slow enough and it won't generate spark.
The flywheel has to turn fast enough so the magnets/windings can "do their thing".

    Bookmark   May 3, 2014 at 9:10PM
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Charging as we speak. Still mysterious about why it cut out so suddenly. The low battery after running for about an hour suggests that the alternator might be weak but I'll deal with that later

    Bookmark   May 3, 2014 at 9:14PM
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I suspect a wiring or switch problem is allowing battery current to reach the ignition system which will destroy the electronic ignition - (CDI)

After charging battery, see if you have any ignition spark when the engine cranks normally. Remove spark plugs to let it crank faster if necessary.

Walt Conner

    Bookmark   May 3, 2014 at 10:21PM
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I agree with your statement, Walt. Another thread here described the same scenario. I'm an electrical engineer and I understand well what would happen to the magnetron if it gets battery voltage to it. I had a hunch that this was the situation but it's good to hear it from others.

    Bookmark   May 3, 2014 at 10:32PM
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It may not be a bad idea to do a test run with a voltmeter on the disconnected kill wire to see if something may be intermittently be sending voltage. Unfortunately, there is scuttlebutt that the new design Chinese made Briggs coils can fail w/o external cause. I've had two fail and I know of others in other shops nearby, so I don't think they are having just an isolated failure. If I have another, I think I'll go to aftermarket for a while.

    Bookmark   May 4, 2014 at 1:06AM
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tomplum, do you have any recommendations as far as aftermarket versions that might be appropriate?

    Bookmark   May 4, 2014 at 12:11PM
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I don't really. I have snuck a Stens or an OEP on a parts order when I wasn't ordering from the Briggs distributor quick enough and had no problems though. At least in recent history. I liked the OEM coils as there was I time 10-12 years ago when I could't get the OEM coil and had to use the Oregon and did have a bad one and swore I wouldn't go back because it ended up being a thorn in my side. Given the choice, a NOS 394891? was the best coil if you could find one.

    Bookmark   May 5, 2014 at 12:09AM
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Thanks tomplum. I will check that out and report back my progress. I don't get to play much during the week so it will be weekend at the earliest.

    Bookmark   May 5, 2014 at 8:49PM
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Bypassed the ignition switch and made up my own OFF-ON with a separate pushbutton start. Didn't solve the magneto issue so I bought one from Oregon. Tractor started right up after installing.
Thanks to all for your help. B&S is checking the magneto for defects. Will post once more when I learn the status.

    Bookmark   May 28, 2014 at 2:28PM
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