Starting problem

Have (2) TO 20s 1 complete eng. rebuild 2yrs ago other had to change cam & gov. all else in tolerance / just taped valves while head was off. Tractor 1 the rebuild / elect. ignition new china carb.Tractor 2 points/ new china carb. Both Extremely hard to start after running & up to temp. Both fire right off when cold. Thinking fuel vapor lock?? if so how to correct or what else THANKS
 
Low compression can cause that as can a weak starter drawing high current which can make weak spark.
You need to check and make sure you have a good blue/white spark that will jump a 1/4 inch gap or more. Also check compression many times a rebuilt engine will be low on compression till broke in well
 
Vapor lock is somewhat rare. It will usually show as loss of power when working
under heavy load on a hot day. Usually it will be associated with gas boiling in
the tank, you can hear it. The fuel line should be steel, not copper, and routed as far from the exhaust as practical, and as straight and down hill path as possible. Be sure the ignition timing is correct and the centrifugal advance is working. Retarded ignition timing causes the exhaust to run hot, promoting the boiling.

Hard warm start is usually spark related. Need to catch it in the act, check the
spark at the end of each plug wire. It should have 1/4 inch spark to ground
minimum.

Weak spark can be caused by many factors. If it's 6v, everything must be right
for it to start, good battery, working generator, size 0 or 00 battery cables,
healthy starter, (worn starter bushings will cause the starter to drag and draw
too many amps), healthy well tuned engine.

If it's been converted to 12v, be sure the coil is correct. It should not be
uncomfortably hot to touch, usually run about the same temperature as the
surrounding components. The wrong coil, or coil/resistor combo, or a failing coil
can cause weak spark after running.

If the ignition checks out, be ready to check the fuel flow when it refuses to
start. Remove the drain plug in the bottom of the carb, catch the flow in a clean
glass. It should have a steady stream of fuel, not slow to a drip or stop
flowing. Look at what is caught, if it's contaminated with water or rust, the
same will be in the carb and tank. The carb will need to be cleaned and the tank
cleaned. If it's flaking rust it's a matter of time till it starts leaking and
will continue to foul the carb and fuel screens. If it's in the budget, a new
tank will solve a lot of grief.
 

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