K301 help please

[jbrewer]

Here's the situation:


I have a replacement 301 that I've never seen run for extended periods of time. I changed the oil, pulled the carb that was on it, and replaced it with a Chinese version to see if the engine was going to run.



This is the engine for the 123 in the other thread. I was firing it up to adjust the hydro/brake linkage and things were going well (we have brakes now for the first time since I've owned this tractor!) but herein lies the current problem:



Engine now starts up but as it warms up, it seems to "fatten up" after 2-3 min and run rich (I think ) till it finally sputters to a stop. It never backfires as an overly leaned out engine will when it craps out.

• Tank is cleaned.
• Sediment filter and housing cleaned
• Carb has been swapped with the original one that came on the engine numerous times (same issue with both carbs)
• Fuel runs freely when I pull the fuel feed at the carb (including immediately after it stalls). It's got gas to the carb.
• Replaced gas tank with tsimple test tank. Same issue resulted
• If I let it sit for 5 min it will start right up, and repeat this cycle.
• Fresh 100% gas
• When running, there's no oil smoke. There's lots of compression.
• When it first starts, it runs well, no missing, etc. at all RPM
• Carb adjustments are at the factory default settings per the manual (both carbs). I've tweaked these as it runs with no change in the end result, so I set back to default settings.
• I can feel a strong stream of air out the front of the head indicating the tins are not plugged up. Engine doesn't seem to be overheated.

I have not done anything with the points/plug other than to check the plug condition (nice white insulator, no soot/oil deposit) when I installed the motor.



I think I have new Chinese carb I could throw at it, but it seems extremely unlikely to me that regardless of the carb, the engine behaves the same way (warm up ok, then start to stumble, then die after about 3-4 min)

Coil?


Condenser?


I do need to check the plug.




Help!



When the engine first started, it would not low idle (engine speed stayed high). I set the governor per the manual and then I had a nice low idle.



I've always thought 90% of small engine problems are fuel problems, and this one acts like it, but I'm at a loss as to what to try.



John