Small Engines (Lawn Mowers, etc.): Simplicity model 5212.5 engine troubles, fuel air mixture, combustion chamber

Question
QUESTION: The engine starts fine, when cold, does not start when hot, does not idle well and when running (ie mowing) it needs the choke pulled out 1/2 way to run smoothly. If the choke is pushed in the engine stalls. Exhaust is not dirty (sooty).

The 12.5 hp hydrostatic tractor mfg number is either 1691234 or 1691235

Sometimes altho not lately, when shutting down the engine it will emit a solid fart-like backfire.  

The engine numbers are: model 404707; type0122 01;code 86102912

thanks in advance,

Patrick


ANSWER: Patrick,

IT sounds like you may have a couple of things going on here.

Do you have a clean air filter?  IF not this is one of the first things you should replace.

The reason your engine is stalling is because its starving for fuel.  By pulling the choke out you are compensating for the fuel/air mixture.

You need to have your carb replaced or cleaned and the essential parts repaired or replaced.  ie nozzle, jet, etc..

The backfiring you talking about is also due to the fuel being able to bypass the fuel shutoff solenoid. The fuel flows past the shutoff needle into the combustion chamber and explodes.

A carb replacement should cost around 100.00 installed by a dealer.  to rebuild and service the carb not much less, but the downside of this is if its serviced and still doesn't work you will then incur the cost or replacing the carb anyway.

---------- FOLLOW-UP ----------

QUESTION: Dave,

thanks much you are right about the filter being dirty, it also is somewhat oily that appears to be coming from the tube coming from the engine rebreather(?).  It recycles air from inside the engine block.  Any idea what might cause oil to come up from that tube?  The emngine is not overfull, never has been and the foam sheath outside of the air filter is always firmly squeezed after cleaning and reoiling.

That fuel is getting past the shutoff needle means that the shutoff needle is bad??

thanks

Patrick

Answer
The shutoff needle could be bad, but its more likely that you have dirt on the tip of it.  This does not allow it to seal properly and allows a lil bit of gas to seep by.

The oily residu could be from a crankcase vacum leak, check all your o rings around the dipstick, or it could be a bad gasket or breather.  Do you have any oil leaks around the valve cover if this is an OHV engine.

Do you have a crack in the breather hose?