Small Engines (Lawn Mowers, etc.): run, small engine mechanic, internal passages

Question
Marc. I have been working on this Lawn Chief riding lawn mower for 3 weeks to no availl. I have adjusted the float so many times. I have another float, needle valve, upper and lower jets. It will crank and run for a few seconds, then die. It will immediately crank again (sometimes) and do the same thing again, 'til I run the battery down. And I give up and say that's it. Then I will rest and go right back at it again.
I have a retired small engine mechanic who has helped me trmendously on things but this one baffles him too.
Think I'll pour the gas out, buy the best grade and try that.
Thanks in advance,
Fred

Answer
If it runs only on choke, there is a blockage inside the carb.  Before I address that, the float should be set to a height that makes it parallel with the carb body when closed.  You need to thoroughly clean the carb, including pushing a piece of tag wire through all of the internal passages and follow up with carb cleaner.  Another problem, according to the symptom you describe, could be the fuel tank vent is plugged.  Try loosening off the fuel cap and starting the engine.  If it's plugged, there will be insufficient fuel flow to the carb.  You would need to replace the cap or clean the vent.  I don't suspect there is a problem with the ignition system or  valves related to heat as the engine only runs for a few seconds.  Hope this helps.