1990 140hp johnson no spark under compression.

[saddlebandit]

What causes spark with plug out and no spark with plug in under compression or at very least a small spark every now in then?

 

[jakedaawg]

Many things, with that said you need to get some things together and do some trouble shooting. You will need a compression guage that preferably is not from harbor freight, many parts stores will rent/loan a known good one. You will need an open airgap spark tester capable of testing up to a 7/16" air gap, preferably one that will test all four at once but not absolutely necessary at this point. The tester is but not the four at once part. You will also most likely need a multimeter and a peak reading volt meter or a DVA adaptor for your multimeter. Assemble this tool set. Check out CDI electronics web page and it has a troubleshooting guide available for free. Many of the parts you may need are probably available on this website at a significant discount as compared to the dealer.

 

[racerone]

A starter motor / battery / cables that are in poor condition will mean slow cranking.------That means no spark.-----Same as your lawnmower / chainsaw.----If you do not pull the starter with some effort it will not start !!!!!!!

 

[saddlebandit]

Its turning at the same rpms with plugs in or out. I made a spark tester with a 2x4, bolt, and nail with a 7/16 gap. I've had it running after rebuilding the 4 carbs. Sometimes it just starts working. I have the fuel tank above the engine so it will gravity feed in. I have another power pack with taped up small boots i could try. I havnt got the flywheel off yet to check the stator or timing base but no sticky stuff. I have electronic experience from ITT. I dont have DVA.

 

[saddlebandit]

it was the power pack.