ignition testing with needle point spark tester

[karl3419]

I have questions about checking the ignition with a needle point spark tester on 70 HP 1978 Johnson engines. First, can this be done on a running engine or is it always done on a crankimg engine? Second, does the sharpness of the electrodes effect the distance the spark will travel? My shop manual says that the spark should jump 1/2". My engine seems to run properly and shows a spark when spark plugs are used but will not show a spark at a 1/2" distance on an inline spark tester.

 

[HighTrim]

Re: ignition testing with needle point spark tester

Are you having issues with the motor?

The sharpness does not matter. If the motor will not jump the 1/2" gap the ignition system is weak. Are you using the starter to crank it while testing? Are you getting at least a couple hundred RPM when cranking?

 

[boobie]

Re: ignition testing with needle point spark tester

Checking spark with the spark plugs tells you nothing. The spark should jump a 7/16" open air gap on a spark tester with cranking rpm around 200-250 rpm.