Briggs motor has me ready to shoot it!!!

Posted on Tractor Talk also.

My Grand Daughter is going to college. She and three other girls rent a house. They bought a mid-priced push mower to mow their yard three years ago. She was mowing the yard a few weeks ago and it ran off speed wise. She shut it off before it blew up. She brought it home to me to fix. It would start but just as soon as it got going it would over speed. DID start hard but would start.
I tore into it and found that the plastic air vane/governor had broken. No problem. I ordered a new one. It came in yesterday. I installed it. I cleaned everything up under the flywheel. I then tried to start the mower. No start. I checked for spark. Light yellow. AHHH the problem. I put in a new spark plug and still poor spark. So I put a new coil on it. Now I have bright blue spark. Tried to start it. No go. Removed the carburetor an cleaned it and installed a new kit. No run!!!! I removed the flywheel to check the shear key. All was fine. I checked compression, right up to spec. I even adjusted the valves. I have brought it up on compression and checked to see if it is firing on TDC. It is. Check for intake leaks, all is tight. You can not even get it to hit one time on starting fluid or WD 40. I have had the carb off three times and it looks fine. Still no hit or fire.

The only thing I can find that I question is that the flywheel has the magnet on one side and a counter weight on the other. At least I think it is just a counter weight because it is not magnetized. I marked the one that is magnetized and it is at the coil at TDC. It seems to spark at TDC.

I am at my wits end on this thing. I came close to using the sledge hammer on it today!!! I gave the Grand Daughter my push mower to get her yard done with.

SO where do I go next??? I am out of ideas on this thing. I have asked the two local small engine guys and they could not think of anything I have not tried. So what do you guys think????

Check if the mower blade is loose. It acts as a flywheel and if it is loose , the mower can be very to start.

When you opened it up to fix the governor, did you remove either the camshaft or the timing gear on the crank? the internal timing may be off. Seems like on some of the Briggs the crank gear is slid up on a pin in the crank and it will slide out of mesh pretty easily.

I can recall 6-7 years ago working on a 3 hp briggs on a tiller. I worked on it a long time before I realized that the intake valve was open on what should have been the power stroke. Opened it up and the cam was way out of time.

(Best I recall we put in a new cam, then when we got it back together the pto bearing was out. It had been low on oil and that was when it jumped time, plastic cam gear and all.)

CHECK THE SHEAR KEY...IF YOU SEE A SLIGHT DIAGONAL MARK...REPLACE.

If it has points and a condenser have you checked those? Had an old one this summer that the points weren't adjusted right and it got to where it did not start.

ok look on the coil /magnatron unit should say this side up , confirm and post back

Stuck or bent valve from over rev.

Top Dead Center is when the piston is at the top of the stroke and the valves are closed.
If you already adjusted the valves, then you should be able to see them to make sure they are opening and closing properly. I think the sparkplug sparks twice during the 4 cycles. Just make sure the sparkplug sparks right before the piston is at the top of the stroke.

What engine? How old is the engine? Honda engines use a rubber timing belt.

Some newer mowers don't seem to need the blade to be aligned to run correctly.

I did have an older mower than definitely needed the blade and blade adapter aligned a certain way to run properly.

I had an old Briggs 12 hp engine that i had to open up to check the innards. This engine must of been run low on oil at one time. I found the recessed "boss" where one end of the cam-shaft fits in the block was worn rnough to allow the cam to lean away from the timimg gear, and fall out of time!
So, i sat down and figgered out how to keep the cam in mesh until i could slide the sump down onto the block. I cleaned the shaft of the cam and also the crank-shaft, and made a loop of masking tape, installed it around both shafts, and installed the sump. It worked great. It held the cam in mesh with the crank gear. And made the job much easier. RJ

I went to the Badger Antique Show today. So I did not have time to look at the lawn mower any today. It will be next week at the earliest, that I will have time to work on it anymore. I will let you know how I come out on it.

Thanks for all of the input and ideas.

Since you had the blower housing off and replaced the coil, is there any chance you have pinched and shorted the small kill wire to the coil when you re-installed the housing? Worth checking.