No spark---Johnson seahorse 25

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jmp

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Just aquired a seahorse 25.It appears ok mechanically,but absolutely no sign of a spark.Can anyone please help with a systematic approach to tracing.I have the usual multimeter and minimal knowlege thereafter.I have no manual to assist with dismantling etc and any useful info would be no doubt helpful please?
 
You give no idication of its age so we have no way of knowing if it has electronic ignition or old fashioned points.

Always quote the full details : make, hp. year and or model no. (Serial numbers for some makes.)

You'll find the model numbr on the mounting bracket and possibly also stamped on a plug on the engine but that may be difficult to find.
This site will id the year of manufacture

The iboats forums is an excellent place for advice on outboards where you'll find separate boards for each make.

iBoats forums
 
Sorry about lack of info. Spent ages on look up site - not very easy. Looks like
1978. Model number 25BAL 78C Serial number B10411. The motor is a long shaft version.
 
With that age it is a bit unncertain whether it has electronic ignition or points magneto ignition.
Electronic ignition has 2 coils mounted on th eengine into which each spark plug lead enters. Thhere is also a encapsulated box mounted on the engine with a couple of plugs with wires one plug harness going to the coils and one under the flywheel.
The points type ignition has the plug leads dissapearing unnder the flywheel.
So the first simple check is of continuity of the plug leads through the coil to ground. Expect a few thousand ohms plus the plug leads which if copper will be zero but if carbon track can be up to 100 K ohms. This check for both ignition types.

If it is points igntion it is time to remove the flywheel to check the poinnts gap and general connections. The points should be noticeably opening and you can clean them with a tiny flat file.
The flywheel is removed by making up a thick plate that can be screwed sown to the top of the flywheel with 3 about 1/4 inch bolts IRRC. You put a piece of metal on top of the centre shaft so that the 3 bolts are well into the thread but thew pllate is pressing on the end of the shaft. Carefully and equally tighten the 3 bolts until with loud crack the flywheel comes free. The 3 bolts can be borrowed from other areas of the motor or leg. it is a good idea after removing the flywheel to quickly palce a large piece of metal across the poles of the built in magnet to minimise loss of magnetism. (or that an old wives tail) untill you refitr the flywheel.

If it is electronic ignition then you can check continuity of the leads going under the flywheel. You should find 2 separate coils of 100 or so ohms on 4 wires.
It is quite likely you need another electronics unit. Confirmed by replacement.

The electronic box contains a rectifier and capacitor which feeds 2 silicon controlled rectifiers. (thyristor) which connect the high voltage from the charged capacititor to the external coil for the appropriate plug. The SCR is fired by a voltage from the other coil under the flywheel. Yes I have tried and failed to fix an electronics box for my 6HP and failed miserably after tediously removing the encapsulation.
So you are looking for an outboard dismantly for s/h parts for an electronics box. You might fall over at the cost of a new box. The parts dismantler may agree to replace the box on a trial basis or leave it with him to fix the motor. It is only minutes work to replace the box and is one of the easier jobs you can do on an old motor. good luck olewill PS my narative really refers to 6HP so I think/hope it is similar
 
Sorry it took so long to find the number on that site. It only took me a few seconds to confirm it but then I knew what I was looking for!

Unfortunately I cannot now find the sort of detail I was hoping to for that model.

Irrelevant I guess but it's a manual start model? I think the B in the number indicates that it was made in Belgium. (the L is for long shaft)

However it appears that it has electronic ignition so no points to worry about.

The first thing to check is the stop switch and its wiring. Use your multimeter to make sure that it is opening OK (its just a shorting switch which closes when pressed) and there are no shorts in the wiring to it..

If it has a safety man overboard kill switch then check that the lanyard is holding that open OK and again check for shorts etc. I don't think it would have had one as original equipment but one may have been added later (Advisable to fit one if it does not have one).

It may have a safety inhibit switch linked with the gear selector. That was something I was hoping to check on. If you can see any suggestion that it does then that needs to be checked in the same way as the others.

Beyond those simple things then really you have got to be suspecting the electonics module (power pack). You can see the HT coils. They have the plug leads attached! The other encapsulated module with a number of wires going into it is the power pack. The only way you can check that is by substitution. There is of course a sensor under the flywheel but they are not normally any trouble. Since you have no spark at either plug I am discounting the possibility that it is the HT coils that are causing the problem.

Obviously check all the wiring for obvious faults and that all the connectors are OK.

You are checking for sparks by with withdrawing the plugs and holding then against the head while turning the engine over I take it.

I hope you do not end up having to take it to a dealer. IMHO it will be worth posting on iBoats if none of these simple checks solves the problem. Tell them what you have checked.

I see Will H has provided an explanation of how the electronics works. Well done Will it's just a black box to most of us.
 
Thanks Will and Vic, very helpful start. Yes the engine has the two ext coils and master box ,so I assume will be electronic.Is it likely the box off my similar johnson 15 may perform the same function for substitution test? I have disconnected the stop wire as a first check,and the gear /start preventer seems
OK .It appears to mechanically obstruct the flywheel rather than electronically.
Will continue the investigation in hope.
Thanks again Michael.
 
[ QUOTE ]
Yes the engine has the two ext coils and master box ,so I assume will be electronic.Is it likely the box off my similar johnson 15 may perform the same function for substitution test?

[/ QUOTE ] It is the same part on a 1978 15hp (part no 581927) but for any other year check the part number in the BRP parts catalogue unless it has the number marked on it
 
Tried to find details of johnson 15 model-- J15BACSD serial no--B17533 to no avail.It should be about 1980 as was with boat new 1981.Trying to find another parts/id search site.Both engines made in Belgium.
 
Different numbering system from 1980! The year letters are based on the word INTRODUCES where I=1 N=2 etc..... E=9 S=0.

So in your case CS makes it a '80 model.

The powerpack is the same part as your '78 25hp.
 
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