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Need Help. 1989 48 HP Johnson

S

snowmanbamf

New member
Alright so I am about at a loss here. I need some help.

I am working on a 1989 48 HP Johnson Outboard with remote electric start.

The Problem- Engine starts and runs, but will not accelerate in rpm. this problem happened all of the sudden and with no alarms, (alarm horn condition unknown at this time) while going across the lake close to WOT.

My Theory- It seams to me that this engine is stuck in S.L.O.W. mode. I looked it up in the repair manual and have performed all the tests that is listed, but cant pinpoint the problem. all wiring and the diode tests ok. it also has no change with or without the sensor pluged in so I cant see it being that.

So What would cause this motor to stay stuck in S.L.O.W. mode? or am I barking up the wrong tree all together? I cant find any other problems with linkage or carberators or any other explination.

I appreciate you help. thanks.
 
SLOW mode, if that engine is so equipped, would be caused by the engine reaching a temperature high enough to set off the warning horn to a constant steady sound. You can check the horn's operation by simply having the key in the ON position, then grounding the TAN wire protruding from the cylinder head (overheat sensor).

SLOW mode is completely reset to normal running mode simply by turning the key OFF then back ON.

Check the compression... what is the psi reading of all cylinders?

Check the spark of all cylinders which should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Note that the gap is important.

Check that the linkage has not disengaged from the timer base... between the top of the vertical throttle arm and the timer base.

Note: Saying that you can't find any other problems or explanation doesn't really tell us exactly what you have already done. Whatever that may be would be nice to know as we could leave out those detailed explanations.
 
What I have done/checked so far-

1. Rebuilt both carbs including running seafoam threw system while running and running fresh priemum gas and oil mix.
2. Re-Link n sinked
3. Checked cylinders with a bore scope for imperfections
4. Checked compression (125 psi both cylinders)
5. checked timing operation and condition
6. unplugged tan lead from temp sensor with engine running, no change, then attached tan lead to good engine ground, no change.
7. tested temp wiring and diode with OHM meter. seamed ok.
8. pulled wiring harness off and carefully removed harness tape and visually inspected wires and diode, then retested with meter, then reinforced diode with a few toothpicks and retaped harness.
 
What I have done/checked so far-
1. Rebuilt both carbs including running seafoam threw system while running and running fresh priemum gas and oil mix.
2. Re-Link n sinked
3. Checked cylinders with a bore scope for imperfections
4. Checked compression (125 psi both cylinders)
5. checked timing operation and condition
6. unplugged tan lead from temp sensor with engine running, no change, then attached tan lead to good engine ground, no change.
7. tested temp wiring and diode with OHM meter. seamed ok.
8. pulled wiring harness off and carefully removed harness tape and visually inspected wires and diode, then retested with meter, then reinforced diode with a few toothpicks and retaped harness.
9. replaced spark plugs, checked gap, and replaced wires.
10. Replaced fuel lines from tank to engine including the one way priming bulb.
 
????----Do you have spark on both leads that will jump a gap of 7/16" or more , yes or no ?----Or if you pull the top wire off will the motor start , yes or no ?---Pull the bottom wire off, will the motor start on that one alone ?---Checked the reed valves ?
 
it has good spark, new plugs, new wires, runs the same on top cylinder as it does the bottom cylinder. the issue is that it will not increase in rpm. give it some throttle and it just sounds like its sucking more air, but doesn't actually increase in rpm. like its being held back. and will run all day long like that. just wont allow itself to get much above an idle
 
Checked the flywheel key ?----Checked fuel pump diaphragm ?-------Checked for a cylinder sleeve out of position ?
 
Check that the throttle butterfly is opening fully at the full throttle setting.
Carefully clean the high speed jets with a piece of single strand steel wire... located horizontally in the bottom center portion of the float chamber, way behind the drain screw.

Snowman... You're evading the question, intentionally or otherwise. Does the spark jump a air gap of 7/16" with a strong blue lightning like flame... SNAP!? The answer of a "Good Spark" doesn't do it.

Adjustable gap spark testers can be purchased at most automotive part stores... or you could build the following.

********************
(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
 
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