725 quit running after a short time

[bgosh]

My 725 starts up real good and runs good,but after tilling for about 200ft. it stops and will not start until it really cools off. Now for 2 questions.Do all 725s breaker box cover have a kill switch built in? and is it possible that after running a short time that copper band in there heats enough to expand to the point where it would kill the motor? I really do get a great spark and this really baffles me.Twice I had to drag it out of the garden. Thank You Stan

[mongolio]

Is it dying from overheating (coil or condensor) or is the carb flooding like my 7016 does? My Simplicity 7016 won't restart until the carb dries out. My Chalmers 916H would overheat & die due to running too lean. Once it cooled, it would fire back up. Just a couple of thought from someone who's dealt with dying tractors....

[johnmonkey]

I'm thinking starving for gas, does it have an in-line fuel filter? or the tank strainer? I remov ethe tank strainer and use a fuel filter. Or it could be your valves need to be grinded, they expand after heating up and that afects the opening/closing of the valves. jh

[Boney]

when i first got mine it had the same problem. first owner put cardboard inside the gas cap. i poked hole in it and solved that problem.

[rsnik]

I am just saying, but here's what I do to trouble shoot the problem. A compression tester is cheap money if you do not already have one. I always start with a compression test. An "official" compression test, used for comparison purposes is always done with the engine completely warmed up, but not overheated. Take an "official" compression test to have an idea what your compression is before the trouble starts. When the engine quits after tilling for a while, quickly remove the spark plug and do a compression test. If the compression is way lower, which it will be if the compression fell so low that combustion stopped happening, you know that you have an internal engine problem, most like the valves as johnmonkey pointed out. The great thing about checking compression first is that if the compression is bad you can stop trouble shooting right there because you now have a known internal engine problem. A real Briggs spark checker is cheap money and well worth it. A real spark checker puts on the correct load and really tells you if you have adequate spark or a spark problem. If the engine passes the compression check, next check the spark to see if it is weak or not regular. You can't, IMHO, get a reliable read on your spark without using a real spark checker. If the spark check fails you know you have a problem in the spark system. Check the kill wire first. If heat is causing the kill wire to ground out anywhere it will ground out the magneto coil. Next check your points both for condition and proper gap. "Don't try this at home" :D, but what I do is, while working safely, in complete darkness, start the engine with the points cover off and see if you see any unusual sparking around your points. That can mean that you have a points plunger problem or that the machine screws that mount the points are not holding for some reason. Most likely it means that your condenser is going, going or gone. Condensers can be aggravating because sometimes the new one you buy was made in China and works worse than the one you took off. You can perform the compression and spark test, if you are well prepared to do so, very quickly and very shortly after the engine dies in the field. If it passes both tests you can move on to fuel problems. I think most of the time contaminated fuel or crud in your tank, fuel screen, fuel line, filter etc which contaminate clean fuel. However you can not check for these issues very shortly after the engine dies in the field, so despite the fact that it is probably going to be a fuel problem I do the trouble shooting first that can be done very quickly in the field when the engine dies. Another approach, if the engine overheats after tilling 200 feet is this: stop after 50 feet, stop the tiller if it's a roto tiller and run the engine at medium throttle in neutral until it cools down to normal and then till another 50 feet. The engine is air cooled and will cool itself way faster when running at medium throttle than when stopped. Also check the intake screen on the flywheel for chaff and any evidence of a mouse nest that may be creating an over heat situation. I once took the side plates off a round hood and discovered that there was a big mouse nest sitting on the rock shaft that was getting sucked out the hole where the hydraulic lift goes and constantly plugging the air intake screen for the cooling air on the flywheel.

[HubbardRA]

Check your valve clearances. I am guessing you have too little clearance on one of the valves. As valves get hotter, the stem gets longer. With insufficient clearance, the engine will get hot and the valve will quit sealing, till it cools down again. I have seen this many times. As was said above, check the compression immediately when the engine dies. If it is a valve you will have little compression when hot, but it will come back up when engine cools down.

[rpickle]

Mouse next around the coil. Overheats the coil, no spark. After it cools, spark is back. Just a thought.