Johnson 50 hp 1972 Coil problem I think.

bagnallt

Seaman
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Jan 27, 2008
Messages
63
Hi ... well after fixing my flywheel key, with the help of you guys, the motor started well and idled great on muffs and in the large bucket. When we took it out on the lake today the motor idled great at the dock. However when we set off and gave it gas it went down to firing on one cylinder. I rebuilt the carbs etc prior to changing the flywheel key so i know its not that.
Ok when we got back home i checked the motor idled great on the muffs both cylinders firing. I did see a crack in the upper coil could this be the cause if it not firing the top cylinder when warm? Also does anybody have the part number for the coil. too..
Thanks in advance for your help
 

tashasdaddy

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Re: Johnson 50 hp 1972 Coil problem I think.

oem# 502890 sierra # 185194.
 

bagnallt

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Re: Johnson 50 hp 1972 Coil problem I think.

Thanks guys... I will get back as soon i I get the coils.. I am going to replace them both..
 

bagnallt

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Re: Johnson 50 hp 1972 Coil problem I think.

Hi guys...
I will be getting the new coil saturday The coil is cracked all the way round and is about to fall to pieces.
I have a question though... while looking at the coil i saw a two purple wires which seem to lead round to the of side of the engine. One of the wires is connected to jterminal box at the the side of the power pack on the 5th connector the other purple wire has a piece of tape on end and isnt connected to anything. I looked in the book and dont see a schematic for this. Could any one help me as to what this wire is for?
Thanks TOny
 

jay_merrill

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Re: Johnson 50 hp 1972 Coil problem I think.

Trace the wires to see if they go to a thermoswitch on the port side of the motor. If so, your thermal choke function (also called the "warm-up choke") has been disabled per the service bulletin (SB #1335) that OMC issued on the matter. There may also be a jumper between terminals 5 & 6 on the terminal block.

Normally, the thermal choke switch will engage your choke halfway, when you place your ignition key in the run position, just prior to turning the key all the way to the start position. If you need additional choke, you engage the choke switch and the choke is applied fully. By jumping terminals 5 & 6 after disconnecting the thermal function, your choke will engage fully with the choke switch alone.
 

bagnallt

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Re: Johnson 50 hp 1972 Coil problem I think.

Thankyo Jay merrill .. You are right.. I have a switch near the ignition key which operates the choke.. Thank you ....
The problem I had was with the coil. I replaced it with a new one and it ran quite well for about 15 mins. Then lo and behold back to firing one one cyclinder... I limped to the dock. cuseda few times. towed boat home and looked again.. and Low and behold the ht wire from the plug to the coil had come out of the coil. I thought I had pushed it all the way in .... Started better than ever on the muffs i even had to reduce the idle.
Obe quick question,,, The HT lead is about 12 inches long..... is it ok to cut it ( I can pull it out of the coil ) to shorten it, the coil i removed ht wire was only 6 inches long.
Thanks for all your help,,
( Have i progressed from Dumb A*** to idiot yet???)
 

bagnallt

Seaman
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Re: Johnson 50 hp 1972 Coil problem I think.

Hi again jay merril
Question for you.... I checked the wires and noticed that the purple wire leading to the port side is disscontected but the perple and yellow is still connected. There isnt a jumper wire between the two terminals you identified. Woudl this affect the running of the motor. for example at the boat maxed out at 8mph according to the gps.
Should i go a head and disconnted the other purple and yellow wire and put a jumper betweent the two terminals??
 

tashasdaddy

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Re: Johnson 50 hp 1972 Coil problem I think.

i will try to dig my 71 50 out tomorrow and look.
 

jay_merrill

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Re: Johnson 50 hp 1972 Coil problem I think.

I would disconnect both wires and tape them up. Having one disconnected still disables the circuit but if the one left connected is to the "hot" terminal and the tape on the other end comes loose, you would short to the powerhead or cowl. If the jumper is not there, go to the marine store and buy a pack of them so that you can make the recommended jump.

Removing the warm-up choke will affect engine operation only in the sense that you will not get the automatic, 50% choke application when you start the engine at times when it is cold. But, you also will not get the artificially rich mixture that this choking scenario tends to create at times when you really don't need it. My understanding is that OMC found that the warm-up choke did more harm than good and tended to cause plug fouling.

BTW - thank Ezeke for this too because he is the one who told me about it. These forums are great because we all teach each other and the pass the knowledge on.

On your spark plug lead ... there should be an instruction document in the box. The coils and leads are made to fit the V4 engines too and the leads are cut long to accommodate that. For your use, yes you should cut the leads but I don't remember the exact length recommended. On my '72 65hp, I have them cut to a bit over 5". Also, when you cut yours and put them back into the coil, screw them in - the post inside of the coil recess is threaded and will draw the wire into that recess, making the connection more firm. Do not over tighten it, though.

Here's a copy of the SB that I mentioned:

JohnsonSB1335.jpg
 

Jacob645

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Re: Johnson 50 hp 1972 Coil problem I think.

Howdy! I recently replaced both coils on my 1975 50hp Evinrude. Make sure that the spark plug boots provided are big enough! For some reason, the ones that were sent with both of mine were the wrong size. They still fit, but for some reason jumped spark to the engine, which resulted in exactly the same symptoms you had. Here's a link to the video! http://youtube.com/watch?v=D3nLqZ3uMaI
Good Luck!
 

bagnallt

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Re: Johnson 50 hp 1972 Coil problem I think.

hi all..
Thank Jay-merril. I will look at disconecting the wire and getting a jumper cable.
And thanks Jacob.. ( I hope i got that name right) I looked at the video and i will check out in the dark this pm to make sure thats not happening. I hadnt thought of that. The plug boots fight nice and tight though but eh. anything is possible with boat motors i guess.

I dont want to take a chance in cutting the coil wire too short so I will call the johnson dealer tomorrow.
Thank
 

jay_merrill

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Re: Johnson 50 hp 1972 Coil problem I think.

If you are getting arcing from under the spark plug boots, clean the plug off. This problem is often caused by "carbon trails."

Also, the jumpers that you need are not wire - they are just small strips of metal with a u-shaped "hump" in them to clear the divider on the terminal block. Each side will have a screw hole in it so all you have to do is to remove both screws, place the jumper and then put the appropriate electrical leads (minus the ones we talked about disconnecting) back where they belong.
 

tashasdaddy

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Re: Johnson 50 hp 1972 Coil problem I think.

i also found on the sierra coils, that you have to assemble the wire and boot. strip back the wire, and wrap around the spring, for good contact. don't depend on the little pin to contact the center wire. then install boot.
 

bagnallt

Seaman
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Re: Johnson 50 hp 1972 Coil problem I think.

Hi thanks all..
Thanks jay for the extra info. thanks Tashdaddy I have just done as you suggested.
I also found.. ,ok i read the instruction sheet fully, the lenght for the wire is 5 inches.. Ok I feel dumb and will read COMPLETELY instuctions next time.
The motor is running great both cylinders firing no smell of gas, idling well on the muffs and in the large bucket i have. Its pumping water better than it ever did. I just pray to the great boat gods that it runs well in the water too.
I even used an hair drier to warm up the coils etc and it didnt faulter at idle.
Thanks again to all. Its great to get help when the manual fails.
 

ritesite

Cadet
Joined
Oct 10, 2009
Messages
7
Re: Johnson 50 hp 1972 Coil problem I think.

dear sir,dont yet know how to post right so im asking you.finally ccranked motor.spins well but no spark.do i have points?maybe coil is bad?what next,take top of motor/flywheel off?test lite will tell me if coil is hot visual will tell me if points are good.why when i turn key to on pos.the motor cranks? bad switch or screwed up wiring.true s/n is 2413557 and mod.is rkl265.very tight budget-ssd. so work must be done shade tree style.am in ca. and must fix before i return home to fla.sorry to put all this on your plate but the best tech forum is all i can afford rite now.thats you boss.please try to heelp me get my boat home.p.s im not a crappy speller,my keys stick.cant catch them all.thank you,ritesite
 

ritesite

Cadet
Joined
Oct 10, 2009
Messages
7
Re: Johnson 50 hp 1972 Coil problem I think.

please read my post under 50hp.johnson coil problem.ritesite post.
 

ritesite

Cadet
Joined
Oct 10, 2009
Messages
7
Re: Johnson 50 hp 1972 Coil problem I think.

wont you please read and reply to post 16 below?i need help.any way to change johnson elect.controls to two handle e/rude?
 
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