I would like your advice as to the next step I should take to get this mower going. It's a MTD 600 series rider from 2001 with a 13 HP Briggs (28T700). This machine ran a month ago but now it won't. The starter will engage the engine and it will "run" while the starter is engaged, but the engine will not run "on its own", without the starter turning it. It seems to completely cycle as the starter turns it. I have:

1. Put in clean fuel
2. Checked for spark (there is one)
3. Changed starter switch
4. Replaced ignition coil
5. Tried to jump from car
6. Cleaned all electrical connections
7. Removed carb and cleaned it with carb cleaner (didn'e notice any water or anything)
8. Tried using starter fluid in the carb
9. Replaced the air filter
10. Checked and replaced the fuse
11. Replaced the fuel filter
12. Oil level is OK (I use synthetic 10W30)

Halfway into last season I went berzerk chasing a faulty safety switch. As a result, I removed all safety switches and completely rewired the machine. The machine ran fine the following 10 times or so I ran it. I'm not sure I cleaned the carb good enough or not. Is there a good online resource about cleaning it correctly? The float seemed fine and the choke and throttle, too. I don't know what else to check or clean on the carb. Any ideas? It might be worth mentioning that the last time I successfully started it was in January when it was very cold (for NC), about 35 degrees F. I let it run for 10 minutes or so just to move the oil around and charge the battery.

When you say it will "run" in the crank mode do you mean it actually runs and when you release the key it dies? If so you may have a miswired ignition switch but the fqact it ran after you wired doesn't make sense. You have done a lot of chasing why the work performed? Is there a reason you replaced ignition coil and the rest or just hoping it woud start.

More info would be helpful, If you IM me with your phone# maybe I could understand better what is going on.
Don

You need 3 things for a controlled explosion, my father always told me when I could not get something started.
Fuel,Compression,spark. What he was saying is that a spark at the right time will explode, when you spray starter fluid in does it pop at all. You may have a stuck valve. Did you check compression. I highly doubt that the timing jumped..

No I haven't checked for proper compression. But I will... I'll let you all know what happens. Thanks!

I checked and the motor does seem to have compression, at least it is reflected in the simple "finger over the spark plug hole test." I will open the motor another time to take a look at the valves. Any other thoughts? I notice today that the needle for the ammeter does not move when I try to start the engine. What wiring problem could allow the starter to engage and generate a spark without completely starting the engine? In a normal successful startup, what happens to make the motor continue without the starter, i.e. when you let go of the key and the motor runs? Maybe the answer to that can help.

The finger test already tells you the valve are closing enough not stuck open, Yes you need to have a constant voltage feed to keep it running that's why the always have a run position and a start on any ignition switch. You implied it doesn't pop at all?

So it really is running with the switch in the start position like your first post??

Do you have a standard coil with points or what's can you send me a wiring diagram sound like you lost the feed to the coil..

No voltage required to run,Works off a magneto and has an electrinic ignition. The key in the run position opens a circuit to ground. If the engine is trying to start when it spins and seems like if it would spin faster would start, you may have compression problem.

Very rarely do we have compression issues on newer machines unless there is a valve or rocker problem. Is this an over head valve engine? If so try checking the clearance should be around 2-3 thousands on intake and 4-6 on exhaust.

Don

All,

It turns out that the flywheel key had sheared, misaligning the magnet on the flywheel, creating an incorrectly timed firing sequence. Hopefully this might help others because this would have been a $.50 fix had I conducted a more thorough preliminary examination.

Me

Flywheel key on a rider is rare, usually caused from a loose pulley on the engine driving the blades and transmission. On a walk behind it is much more common from hitting something and no belt to cushion the blow.

Check the bolt holding pulley on, sheared key is a sympton of another problem?

Congrats,
Don

Well I can tell you this, you are using the wrong kind of oil. All brigs engines are designed to run off single viscosity 30 weight oil, definitely not synthetic.