Joe Reeves
Supreme Mariner
- Joined
- Feb 24, 2002
- Messages
- 13,262
1977 6hp Johnson - Magneto Capacitance Discharge ignition.
BoatThings.... Frankly, in my 30+ some years at the bench, I was never really interested in the actual ohm reading of the coil(s)... what concerned me more was the continuity, as follows:
*********************
(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)
Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.
Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.
Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire... the spring should be touching the fanned out center wire Poor or no continuity of a coil is one reason for s/plug fouling.
********************
NOTE that a inline spark test light will not give a true reading of the powerpack or ignition coil's quality. The spark test requires a tester with an adjustable air gap.
With all spark plugs removed,the spark must jump a 7/16" air gap with a strong blue lightning like flame... a real SNAP. Anything else presents a problem.
********************
(Spark Tester - Home Made)
(J. Reeves)
You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:
A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.
Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:
..........X1..........X2
.................X..(grd)
..........X3..........X4
This can obviously be modified to a 6 or 8 cylinder setup tester.
********************
If memory serves me properly, the fuel pump operates off of the top cylinder so if the diaphragm was leaking, that would affect the top cylinder... and apparently that was still firing enough to run for a short time after the engine failure... so the fuel pump diaphragm should be okay. However, I'll list the diaphragm test procedure immediately below just in case you would want to make sure.
********************
(Fuel Pump Diaphragm Test)
(Two Hose Type Only)
(J. Reeves)
Note: This pertains only to the regular Two Hose type fuel pumps.
Leave the hoses attached to the fuel pump. Remove only the two screws that attach the fuel pump to the powerhead. Re-insert those two screws and install a nut to each of them so that the fuel pump is securely clamped together. With the fuel line attached to the engine, pump the primer bulb while observing the pressure/vacuum operating hole on the back side of the fuel pump. Should any fuel leak out that hole, the diaphragm is faulty.
If the diaphragm is faulty, the fuel pump will require rebuilding or replacing. Note that repair kits are not available for all fuel pumps, in which case replacing the pump would be necessary.
********************
The mention of a "power loss accompanied by a nasty racket, however does make me wonder as in my time at the bench I've had a lot of engines running on less than their numbered cylinders... BUT... no racket. However, perhaps our individual description of racket varies so putting that aside...............
********************
Miscellaneous:
Best to use new Champion QL77JC4 plugs, gaped to either .030 (long life) or .040 (super strong spark). Even though the actual running hours are short... age and the elements do take their toll on those items.
The graphic of the bottom s/plug... it really does have the given effect of being water, BUT if it burns.................!
I'll just have to take your word on the compression readings, however in our line of work for years on end, and coming across a 30 psi difference. To us, that spells disaster engine wise. Anyhow...............
Let us know what you find.
BoatThings.... Frankly, in my 30+ some years at the bench, I was never really interested in the actual ohm reading of the coil(s)... what concerned me more was the continuity, as follows:
*********************
(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)
Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.
Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.
Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire... the spring should be touching the fanned out center wire Poor or no continuity of a coil is one reason for s/plug fouling.
********************
NOTE that a inline spark test light will not give a true reading of the powerpack or ignition coil's quality. The spark test requires a tester with an adjustable air gap.
With all spark plugs removed,the spark must jump a 7/16" air gap with a strong blue lightning like flame... a real SNAP. Anything else presents a problem.
********************
(Spark Tester - Home Made)
(J. Reeves)
You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:
A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.
Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:
..........X1..........X2
.................X..(grd)
..........X3..........X4
This can obviously be modified to a 6 or 8 cylinder setup tester.
********************
If memory serves me properly, the fuel pump operates off of the top cylinder so if the diaphragm was leaking, that would affect the top cylinder... and apparently that was still firing enough to run for a short time after the engine failure... so the fuel pump diaphragm should be okay. However, I'll list the diaphragm test procedure immediately below just in case you would want to make sure.
********************
(Fuel Pump Diaphragm Test)
(Two Hose Type Only)
(J. Reeves)
Note: This pertains only to the regular Two Hose type fuel pumps.
Leave the hoses attached to the fuel pump. Remove only the two screws that attach the fuel pump to the powerhead. Re-insert those two screws and install a nut to each of them so that the fuel pump is securely clamped together. With the fuel line attached to the engine, pump the primer bulb while observing the pressure/vacuum operating hole on the back side of the fuel pump. Should any fuel leak out that hole, the diaphragm is faulty.
If the diaphragm is faulty, the fuel pump will require rebuilding or replacing. Note that repair kits are not available for all fuel pumps, in which case replacing the pump would be necessary.
********************
The mention of a "power loss accompanied by a nasty racket, however does make me wonder as in my time at the bench I've had a lot of engines running on less than their numbered cylinders... BUT... no racket. However, perhaps our individual description of racket varies so putting that aside...............
********************
Miscellaneous:
Best to use new Champion QL77JC4 plugs, gaped to either .030 (long life) or .040 (super strong spark). Even though the actual running hours are short... age and the elements do take their toll on those items.
The graphic of the bottom s/plug... it really does have the given effect of being water, BUT if it burns.................!
I'll just have to take your word on the compression readings, however in our line of work for years on end, and coming across a 30 psi difference. To us, that spells disaster engine wise. Anyhow...............
Let us know what you find.
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