C won't start again when I shut it off

Hi, I apologize in advance that this is a long post, but I feel I need to explain the situation completely in hopes that some of you guys might be able to tell me what's going on with my tractor. I recently bought an Allis Chalmers C with a side mounted sickle mower to mow my 2 acres of hay. It's my first AC tractor and I was very impressed with it for the first crop. It has a magneto and the starter and lights run off a 12V neg ground setup with a generator. For the first crop of hay the tractor started right up every time without even having to choke it! It ran great the first day when I mowed. The next day when I was raking it started to miss, but still kept running and starting OK. I thought maybe it was the gas I was using. I didn't think to buy premium so there was some ethanol in it... maybe 5-10%? A friend also suggested it might be a good idea to buy a Lead substitute to add to the fuel, so I picked some up at the local car parts place and added some to the fuel. While I had it in the garage I checked the plugs and wires and I realized that a couple of plug wires had worked loose so I tightened up the ends and put them back on. The tractor seemed to run fine and I parked it until we were ready for second crop. It seemed to start a little harder when I went out the other day to mow, but it was running OK. I mowed for about half an hour and I had to stop for something and shut the tractor off. When I tried to start it again it would not start... at all. It turns over like crazy with the 12V battery, but wouldn't start. Had my wife pull me back to the shop with the truck so I tried pull starting it and half way to the shop it started. Ran for about 30 seconds then quit. I spent the whole day yesterday messing with it. I found a bad wire from the switch and replaced that. I checked to make sure that gas was getting to the carb and that was OK. When I checked to make sure I had spark I noticed it was weak so I replaced the plug wires, but that didn't help. I tried cleaning the plugs and checked the gaps, but that didn't help either. I finally went and bought new plugs and I drained out the gas and put in fresh Premium gas with No ethanol, installed the new plugs and it started right up and ran like a new tractor!! Again this morning it started right up and I went out to mow again. I had to turn off the tractor for a few minutes while I adjusted the mower. When I got back on the tractor it would NOT start!! It turned over like crazy, but no start. I kept trying and FINALLY it started and ran fine! I got back to the field and just as I started mowing it quit. I'm really hoping to find someone who can tell me what's going on with it!???

As I read your post It seems to me that you do not have an engine problem. I would say you have one of two problems. Intermittent fuel restriction or intermittent spark. For an intermittent fuel restriction it can be anywhere from something sliding around in the tank to something in front of the power jet or some where in-between. I bought an Oliver 66 and mounted a cycle mower and when I started mowing hay it would cut out and die on only one corner. It would start up and run until I cam to this same corner. Long story short I found a large flat washer in the tank. On my Allis C that I mow with I have several time had it stop like yours and found the neck of the sediment bowl neck plugged. It always happened at the far end of the yard. Until I could get time to clean the tank a quick fix was to remove the gas line at the carburetor and blow compressed air back into the tank. I also had the problem in this picture where a build up was in front of the power jet. You can burn you regular pump gas without any problems. That is what I burn in all of my gas tractors. Oliver 1850 down to my lawn tractors.

For intermittent spark, check points first but could need a magneto rebuild. On a magneto I have only found points to be intermittent problems. Others have had coil problems. For weak spark I have found magnets that lost the pull on a screwdriver to be one problem. All of my magneto coil problems over the years have been no spark any time.

If its NOT a fuel flow problem (When it stops open any carb bowl bottom drain cock to insure a steady full steam of gas drains out) but an ignition problem (When it stops pull a plug or coil wire to see if its making a good strong blue spark), my suspects would be the Points (insure they are gapped correct, clean and not carboned or pitted or burned),,, the Condensor (fails once warmed up),,,,,,,,,,,,or the coil is failing once warmed up.

John T

Certainly no reason to buy premium gas....never was used years ago, and no reason to blame E10 ethanol.

I appreciate the quick and thoughtful replies! I think the main clue here though is that up until yesterday it did NOT quit running at all. In fact it ran great! The initial problem was that when I shut it off it didn't want to start again. Letting it cool down did not make any difference so I don't think it's a heat issue. I checked to make sure that there was fuel to the carb and it still wouldn't start. Someone suggested it might be turning over too fast with the 12v battery that the magneto isn't able to create a good enough spark, but if that's the case why did it start SO GOOD for the first couple of months and then just change all of a sudden? Also the last time I tried to start it I was frustrated so I just kept adjusting the throttle and trying to start it. I didn't change anything else and then all of a sudden it backfired and started after about five minutes of trying!?? I don't think it's fuel related and when it runs, it runs GREAT! What am I missing?

I'll agree with the others on ignition problems. The coil and/or condenser could have heat failure or the armature needs remagnetized. It takes more amperage to make a hot coil spark than it does a cold one. What brand of plugs did you install? Champion? Replace with AC or Auto-Lite.

Thanks so much for the advice! I did use Autolite 295 plugs. It's not even starting the same when it's cold now. It used to start within two seconds without choking whether cold, or hot. I went out this morning and it started without doing anything, but it took several bursts of the starter over 2 minutes for it to take off. I went out and mowed for 45 minutes until the mower broke and it ran fine the whole time until I turned it off. Now it won't start again. I guess my next step is to open up the magneto and replace points and condenser? How would I check, or re-magnetize the armature?

When you dang sure know it is a fuel problem you'll probly find it is an electrical problem. Then again when you are dang sure it is an electrical problem you'll probly find it is a fuel problem. Rather than have a sure thought when trouble shooting it is best to run each item all the way before jumping to the other. When you are checking for the electrical side you either have spark or you don't when you are trying and it is not starting. Since timing is not the issue and you seem to have compression and you find you have a good spark you would be left with a fuel problem. You can remove number four spark plug and with the wire on it ground the base of the plug to the tractor and run the starter at the same time and see what the spark looks like. The fuel side would mean you would need to disassemble more to find the problem. When opening up the carburetor bowl bottom you would need to draw out a couple cups of gas or more to see what flow you are getting. I still would not be surprised if you didn't find your problem in the neck of the sediment bowl or something in the tank sliding around. When fines clog the inlet of the sediment bowl it first slows the flow for a time before it stops the flow. That is why my first check after I know I have spark is to blow compressed air from the carburetor back into the tank. That quickly tells me the line is clear enough for fuel when I hear the bubbles. If that is not the problem I can remove the carburetor and check the jets and insides.
All an engine needs to run is Spark at the proper time, compression and fuel at the proper mixture.

Maybe too much fuel, it's flooded.