Re: 100 hp mariner late 80's early 90's 4cylinder 2 not running
Troubleshooting a problem in a logical sequence will help you determine which way to proceed to zero in on the problem.
The compression test will tell you if you have a mechanically sound cyl/piston. The actual # can vary quite a bit with the quality of the gauge used, the important thing is that all cyl's read within a very tight range, within 10% or less of each other. A cheap tool may only read 85 or 90 PSI, as long as all cyls read near that, fine, a quality tool may read 110 to 120, again, as long as they are near the same.
Next is a spark test using a 7/16 inch air gap to see a nice fat blue arc capable of arcing under compression. This only tests the ignition system at cranking speed, the stator actually has two sets of generating coils, a low speed series used at cranking and running below 2500 RPM where the high speed coils begin to take over voltage generation for high speed running. Here is where a DVA Meter or any volt/Ohm meter and a DVA Adaptor can be used to test the high speed coils while cranking, if they cannot generate within the acceptable range at cranking speed then the high speed coils cannot generate well enough for high speed running.
There is always the possibility of broken trigger wires abutting and working, then failing as the throttle is moved and the wires are flexed. During the spark test it may be a good test to disconnect the throttle cable and while cranking and watching the spark, move the throttle lever at the motor all the way from idle to WOT and back. If spark fails at any point during throttle movement then the trigger wiring is suspect. It is also a good idea to remove the spark plugs to relieve load on the starter and battery during spark testing, and grounding the other three plug wires to prevent any errant sparks from either biting the #### out of you or igniting and gasoline fumes that are blown out of the cyl's.
CDI Electronics has what may be THE best Ignition Troubleshooting Guide ever written, available for free download, find your particular ignitions section, study it, as it details very clearly which wires to test and how to test them.
CDI Electronics Practical Outboard Ignition Troubleshooting
So after confirming compression and spark, the only thing left is fuel and adjustments. Be sure to double check fuel delivery to the carbs, air sucking into the system from old cracking hoses or a leaking fitting will not allow the fuel pump to fully fill the upper carbs, the motor will not perform. Two good tests, disconnect the fuel hose between the fuel pump and carbs, point it into a suitable container and crank the motor, you should see a strong pulsed fuel stream the diameter of the fuel hose and spurting out with good force, any less and suspect the fuel supply hose and fittings. The second test it to temporarily replace that section of fuel hose with a clear hose, hook up the ear-muffs and water hose, start and run the motor watching to see if any air bubbles keep passing thru indicating air sucking in anywhere before the fuel pump. O-rings in quick disconnect fuel fitting die, sealing fine when pumping the bulb but failing when the fuel pump sucks on it.
Time spent on these details will soon detect the problem, just remember to remove that clear hose once finished with testing and repair, clear hose is NOT RATED and is NOT APPROVED for fuel use, only as a temporary tool to check for a problem.
Check each of these and repost what you find.
