Tractor Repair: 1950 International Cub starts hard, carborator, charge battery

Question
Hi,
Basic information:
Make:  International
Model: Cub
Serial Number:  on body:  351686-R1, on motor:  J4130016
Age:   1950 (59 years old)
Hours: unknown, many.

I use the tractor 2 to 5 times a month except in winter.  Can run for a couple of hours when I do use it.

Problem:  Used to start on first crank.  Now starts only with many, many tries using electric starter, sometimes not at all.  It will start on tow in third gear after 50 to 100 ft pull.

Things tried:
Always use hi-test gasoline.
Battery new last year.
Charge battery when it fails to turn engine quickly.
Pulled each plug to check for spark.  Spark seems OK (blue/white color), although the plugs are dirty.   Black and damp (gas or oil, not water).  Some carbon build-up, which I cleaned up.  Plugs about 5 years old.

Replaced starter motor about a year ago.
All wires were replaced about 5 years ago.

When the tractor is running it runs smoothly and normally I can stop it and restart it without too much trouble, unless it has cooled down, in which case it may or may not start with electric starter (a tow will work).

Typical starting attempt for a cold start on a 50-60 degree day:  
1) try without choking.  
  Starter turns engine turns over pretty quickly, but no sound of life.  After a few such tries, engine will make a weak putt, electric start kicks out and spins, try again.  Now each time I will get a putt from the engine but it will not come to life.
2) try with choke, first a little, then full.  Basically same sequence as explained above.

3) In desperate, get a tow.  Get a puff of black smoke, then it comes to life and all is  good.

My questions:
1) Since the tractor works great once started, it seems that the carborator is OK.  Gasoline is getting through.  But, as I am no expert, do you recommend pulling it and having a mechanic rebuild it?

2) Although the plugs and wires are 5 years old, I have not used the tractor that much.  I did not think it worth changing them?  Do you agree?

3) Not sure if I should replace distributor and/or magnito.  

Any suggestions would be much appreciated.

Thank you for your consideration.  

Answer
Hello,

  There are several things that can cause hard starting problems such as yours.  Gasoline that is more than a couple of months old can cause the exact symptoms you are having - hard starting, but runs good once started.  Gas does not stay fresh very long so if it has been in the tank for awhile, drain it out and put in fresh gas.  It does not matter if it is hi-test or not.  Spark plugs that are black and wet should be replaced.  No amount of cleaning will make them perform like new, especially with today's unleaded gas.  If an engine is flooded once, the plugs will never be the same and should be replaced.  While changing the plugs, do a complete tune up and replace the points and condenser.  Inspect the choke linkage and make sure the choke is closing all the way.  If it runs good once started, then the carburetor itself should be OK.  Make sure the valve clearances are OK and adjust if necessary.  If these things do not help, then a compression test should be performed on the engine.