Slow mode no alarm

[Bordeaux33]

Hello everybody,
I am new to this site so pardon my possible errors...
I am the proud captain of a 1999 20ft Hydrasport powered by a 2002 Jonhson (J150PXSNF).
I bought this vessel 4 months ago.
I had the engine checked at the time and the carbs rebuild (by official dealer).
It was running fine until last weekend when suddenly on our way back engine start shaking and kind of choking...
When i lowered the rpm it went back to normal. Seems like it is running in SLOW mode though no alarm went off.
Lately it was harder to start the engine, but will always ends up running.
What can cause a SLOW mode when no alarm are on??
Thank you for your help.

[Joe Reeves]

Does the warning horn emit a short beep when you turn the key to the ON position? (engine NOT running)

The SLOW mode is activated if the engine starts running too hot... but before the engine is hot enough to do any damage.

If the engine goes into the SLOW mode, the rpms drop to 2500.... did that take place? That scenario resets when you turn the key OFF, then back ON.

[Bordeaux33]

Hello Joe,
The alarm led does light up and off one by one with short sound when i turn the key.
Though my tacho is not working it did sound like running around 2500rpm when problem occured.
I didn't run it after.

[Bordeaux33]

Hello Joe,
The alarm led does light up and off one by one with short sound when i turn the key.
Though my tacho is not working it did sound like running around 2500rpm when problem occured.
I didn't run it after.

[Bordeaux33]

I have to mention that I have to make it run slower, it won't do it on his own.
And was running fine then.

[Joe Reeves]

The tachometer NOT working could indicate a serious electrical problem. A test is available as follows. Many boaters have sworn that this regulator/ rectifier problem (if it exists) has an effect on the ignition system.

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.

Normally the Gray wire leading from the tachometer is attached at the terminal strip to another Gray wire which leads from the water cooled voltage regulator/rectifier...... remove the gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.

[Bordeaux33]

Hi Joe,
Thank you again for your time.
I will definitely test my tacho before getting another one. But from my understanding if i have a default reg/rec I should have a charging issue (which I don't) correct?
And best case scenario i will solve my tacho issue but not why my engine went in slow mode. Is that correct?

[Joe Reeves]

If the engine was going into S.L.O.W/ mode, the warning horn should be sounding constantly/steady and the rpms should drop to 2500 rpm. From, what you've said, neither of these conditions take place.

Remove the spark plugs and take a compression and spark test so as not to overlook anything.

What is the compression psi of "all" the individual cylinders?

The spark should jump a 7/16" air gap with a strong blue lightning like flame... a real SNAP!... Does it? Note that the gap is important!

********************
(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
***************

Yes, you are correct... fixing the tachometer (if it is fixable) will not cure the "going into SLOW" mode, if indeed that's what the engine is doing, but it will get that question out of the way... that is whether the tachometer is faulty or not.

And again, yes you are correct in that a faulty regulator/rectifier would certainly affect the engine's charging system if the reg/rec was faulty... another reason to check the tachometer.

For now... when you check the compression and spark, which is important and normally the first act of trouble shooting which we bypassed originally due to a suspected S.L.O.W. mode encounter.