if the tiller doesn't have a battery/ electric start mode, i don't think it hurt anything to leave it on. If it has to be plugged into house current to start, same deal.
but, if you have a battery to start the machine, then you might have caused some damage, especially if you left the key on "ON" How old is the battery, if it has one?
Usually life of an electric start type battery is 2 years, although some extremely lucky person might get 3 seasons from a battery.

Thanks for the reply,
No it doesn't have a battery, just funny that it wouldn't start. It was kept inside a shed, so not wet. It's getting gas, but will check spark tonight, was worried that it had burned out the points or something. Adjusting the points and ignition is listed in the maintenance schedule, but notes it is to be performed by the dealer. In the manual I have, it doesn't give the location or the specs for the points.

Leaving the switch on IMO done nothing. Some trimmers have switch that spring loaded to the on position and when you want to shut them off it spring loaded to the on position. This prevent people from frogetting to turn the switch on. All the switch does is break ground to prevent coil firing through the spark plug wire to the spark plug. if flywheel an't turning nothing is happen.

Don't have fuel cutoff valve does it? IMO first you need to know if you getting spark to the plug? remove the plug lay it on the head (metal Part) turn the switch back on and pull the rope. You should see nice blue spark. Now that you know you got spark spray some carb. cleaner in the spark plug hole before you put the plug back in. It should fire off the carb. cleaner? If so you problem IMO lies in fuel flow problem. Could be as simple as clogged filter or just priming it with carb. cleaner. it also may have sticky needle in the seat which may require cleaning the carb. or cracked fuel hoses. Last question does it have primer button? if so does it circulate fuel from the tank through the carb. and back to the tank?

Your F400 Tiller has the Honda G150 3.5hp flat head engine. Last made in the early 1980's and replaced by the GX120-140-160 series. Good engine, but "old school".

Your engine has breaker points and condenser, which are located under the flywheel. A few later engine were fitted with transistorized ignition. If your coil is outside the flywheel, you have electronic ignition and your life got earier, but not necessarily less expensive. No coil visible means breaker point style coil, and everything under the flywheel.

You have to pull the flywheel to get at the points. That's why Honda suggests a dealer. You need a tool to hold the flywheel while you remove the crankshaft nut, and then you need a puller to remove flywheel. Can be done without special tools, but if you haven't done it before, you can damage the crank, flywheel, and/or block. And, as I'm sure you know Honda parts prices will curl your hair.

Once points are exposed you either need to replace, or if only lightly burned, file or burnish. Use an automotive point file. Don't take off anymore metal than need to clean up. Adjustment is to .020 gap at highest point. adjustment is done to the "fixed" contact. There will be a hold down screw and the point frame will have an oversized slot to allow adjustment. Could also be a bad condenser, so after I did the points, I'd dry fit back together to see if you have spark, before you crank everything down to full torque. You may have to go back under the flywheel to replace condenser.

As for fuel system, the G150 has a petcock under the tank, and then a fuel line to the carburetor (Keihin is mfg). I believe it has an "OFF", "ON", and "RESERVE" position. There is no primer or return line. Carb has a choke plate, and I'm not sure whether it is manual, or integrated with the throttle cable and governor assembly.

In my judgement, best practice is to close the fuel petcock after every use and then run the engine dry. Others will disagree, but I have generally had less trouble with varnish and corrosion build up in my carburetors.

OK had time to look at the tiller today and found it is getting some spark when I remove the plug and spin the engine. So I tried some ether down the carb and it would start and run as long as I kept spraying ether down it. Replaced a broken fuel line and removed the carb. Removed and cleaned the float bowl, needle inlet, the main jet (I think), but not the metering tube under the jet. I could see it and it was clogged so I squirted cleaner into it and compressed air through all passages I could find. After looking at some diagrams online ( I dont have the Shop Manual) of the carb, I see this metering tube or jet has other orifices in it that cant be seen from where I was looking, so probably will need to take it back apart tomorrow and try to get that tube out to clean it. Anyone know how to get it out?
By the way, thanks much for the replies and the info on the location of points and condenser, I hope at this stage I dont have to deal with that yet, but will if I have to, I love my Old School honda tiller.

If your motor was recently running OK it seems a quick cleaning should work. Such as, with compressed carb cleaner to dissolve and flush varnish, fine wire to rod ports/orifices and verify opening are open/clear and compressed with a small direct pointer to direct higher pressure directly into orifices/ports. If that does not clean it, my suggestion is to strip the carb and soak it overnight then check the orifices/ports with wire and compressed air again verifying every opening is open. Reassemble, Adjust & Good Luck! loger

PS. Do you use Stabil etc in your gas to prevent varvish etc??