Have a 1971 evinrude outboard and the spark comes and goes any ideas?

Question

the motor will start and run great sometimes and other times it doesnt have any spark at all

Answer 1

Most likely the point gap is too small.

Answer 2

switch box   or stator   do you lose one side    than its the switch box

Answer 3

Bad coils - look for cracked an broken insulation. Sometimes the coil will short out. Had the same problem with a1960 Evinrude. Coils are cheap.

Answer 4

Really need more information on the engine to make an educated guess. Horsepower, # of cylinders, type of ignition, etc.

We can guess all day, but the answer could be totally different between a one cylinder and multi cylinder engine.

The coils on Evinrudes have plug wires that just push into the coil. If it's a one cylinder, check that. If it's multi cylinder, that's not likely.

If it's got points, it could be the points. If it's got a stator, it either works or it doesn't no sometimes, so rule out the stator.

If it's multi cylinder and has a stator, I'd check the kill circuit before anything else. To check that, take the cover off of the power pack and remove the black wire(should be top right side in the power pack), with that wire removed, turn the engine over and see if the coils are firing. If they are the kill circuit has a problem. Or the ignition switch is bad.

Answer 5

Does the spark go only when the motor is warm?  If so, coil problem.  

If the spark comes and goes any time, whether the motor is warm or not, I would check, clean and tighten every connection on the motor.  For its age it is likely there is a bit of corrosion.  I would check the condition of the leads- either run a multimeter over them, check the resistance (should be able to find acceptable resistance in a manual or on the net) also see if the resistance changes as you manipulate the lead (looking for a broken lead).  

Check also the spark is not arking out somewhere.  Easiest way is to try starting at night

When you find it is not sparking straight away put a screwdriver into the end which clips onto the spark plug and ark the screwdriver onto the block (hold the insulated bit) you should see a strong blue spark.

Good luck