Small Engines (Lawn Mowers, etc.): my mower wont start, cold briggs

Question
QUESTION:
    Hi I have a 4.5 hp B&S engine on a murray lawn mower and it wouldn’t start yesterday when I attempted to start it. It was –15 degrees but still

The engine is a 4.5 hp B&S
Model# 10G 902
Code# 03022855
Type# 0189 B1

Mower
Model# 204210X31A
SKU#101-763
Serial# 7515 306432F323

     
  The motor wont start it has good spark, good compression (112 P.S.I) and I tried starting it with quick start. Any suggestions appreciated.

Thanks
Derek  


ANSWER: At -15, that would be more than enough to keep it from starting.  Personally I wouldn't do anything to it until I had warmed it up.  Also, at that cold of a temperature you can ruin a small engine pretty quickly from the oil being gelled.  

In my shop, we won't try starting engines on cold days for the first couple of hours unless we have a heater pointed at them.  And our coldest days are in the low 20's.

So I'd get it warm first and try it.  Let me know if it still won't start.  Thanks, PK.

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

QUESTION: thanks P.K Jones

    the engine did start after heated but when it started it would rev- up then it would miss a couple times then catch again and blow black smoke. What should i do next?

much appreciated
Derek

Answer
If you have 30 weight oil in the engine, the oil temp needs to be above 30 degrees.  What you're describing is an over rich condition.  This can be caused by a stopped up air filter, and internal problems in the carb.  You have a very basic carb and the primary thing to suspect is the fuel nozzle or pick-up.  

This should be a plastic carburetor.  I would expect extreme cold would cause a problem with the fuel nozzle as it's metal and is going to shrink and swell differently than the carb body.

Also, this is an all aluminum engine and is going to move around a good bit.  You'll have problems with valves not seating correctly because they're much harder than the block and won't shrink at the same rate.  The cylinder is going to move around more due to the cold and the block is going to change.

You have to consider that this engine was designed for summer temperatures.  With that in mind, I wouldn't try and do anything to it as you can't really diagnose the problem.  It wouldn't hurt to pull the carb and clean it out and replace the fuel and clean the air filter.  But if the problem persists, I wouldn't spend any money trying to repair it because there's no way to know for sure what the problem is.

Thanks, PK.