Why is my 1250 dying?
 

I have a 1250 that I just replaced the head gasket on, and decarboned as well, rebuilt the carb, replaced the spark plug, points, condenser, and coil. It starts right up, better than it ever has for me, but after 10 min of run time it dies, it blew the dip stick out. Is it overheating? Inset the carb to the factory settings in the manual. So maybe it is running lean causing it to overheat? It runs longer when not under load, if I let it sit in place and run up the throttle it will sound fine but after a little while it will begging to pop out the exhaust and run rough. Shin it happens faster when mowing and will actually stall out. I'm stumped. Please help. I looked and couldn't find any one who had similar issues. Thanks

Is the crankcase breather plugged?:bigthink:

Did you resurface the head when you had it off? How about retorque the head after one heat cycle? Did you adjust the carb once the engine had warmed up? You can't just set it to what the book says. That's just a starting point...you have to adjust it, on your own, from there once the engine has warmed up.

I had the same thought about the crank case breather, I haven't been back out to the tractor yet tonight, yes I resurfaced the head, yes I retorqued the head after a heat cycle, no I have not adjusted the carb from what the book says. I will check the breather and hopefully not mess up the carb while trying to adjust it tomorrow. Thank you for you inputs.

1.) Did you use the right coil?
2.) Is the condenser grounded?
3.) Fuel line clear?
4.) Float height correctly set?
5.) Gas flow well through the filter screen in the tank?
6.) I'm assuming you haven't had the breather off to adjust the valves. Probably could use a valve adjustment.


Already mentioned:
1.) Plugged engine breather. (Possible)
2.) Tune the carb. (Absolutely necessary)


Could also be:
1.) Engine is shot.
2.) Sticking exhaust valve.


Blowing the dipstick out can only be caused by 4 things: 1.) It wasn't in all the way. 2.) O-ring on the dipstick is shot. 3.) Crankcase breather plugged. 4.) Motor is shot.

You are going to have to narrow it down some......

When it dies, will it restart right away?

Does it smoke at all? One of my tractors has a plugged breather and it smokes like a mosquito fogger. It's the next on my list to tear down and fix.

Yes it will start back up after it dies but cranks just a touch longer than the initial start up, yes the gas line is clear and flows very well, no I did not adjust the valves or check the breather. The coil is an after market one but is said to be "correct" I will put the original one back on and see if it helps. I set the float height when I rebuilt the carb with the instructions and measure device in the rebuild kit. Since I have never rebuilt one before I'm sure it is close to right but probably not perfect. And yes the condenser is grounded like it was originally.
Thanks again for all the input JMech you are always full of knowledge on these matters. Thanks for your time everyone.

No smoke, runs very clean and smooth, only the throttle is a little loose I have to hold it up, if not it will slowly go back down to about half throttle.

Popping out the exhaust is usually either too lean mixture or stuck exhaust valve. after it stops and cools do you hear a clink ? Pull and replace the exhaust valve, ream the guide with a wire brush reamer.

Just wanted to extend a yuge thank you to all those who chimed in, and especially to @J-Mech due your thought of the coil. You knowledge of these machines is astounding, I would have never thought that the coil was causing my problems. Today I checked the breather to see if it was clogged, it was not. While in there​ I adjusted the valves, they were off a couple thousandths but not much. Then followed the carb adjustment steps in the book, but still couldn't get it to run smooth at high rpm. Then remembered J-Mech mentioned the coil so I swapped it back and wala it smoothed right out. A few more min of carb tweaking due to trying to set it with the wrong coil. Now it runs great but cracked the new muffler, so on Monday I get to take it to work and weld that back up.