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Johnson 4hp only one spark

B

Bulldogste

New member
Hi,

let me start of by saying hello to all.

i have an issue with a 1979 Johnson 4hp outboard 4BR79D

i did phone my local boat shop but they were not interested as said there is no money to be made in small out boards, I was like cheers for that!!!

i went to start it the other night but had no joy, just for info it had been running fine the previous week.

started out checking basics and noticed it had only one spark on the top cylinder, to my horror I pulled the top off it and noticed it had points, i have not worked on anything with points for about 20 years haha.

stuff I have done to try and isolate the fault.

1. Checked spark plug leads. Continuity check switched spark plugs ect.

2. Switched coils and condenser over, still had spark on the top cylinder as before the switch. I was convinced this would have sorted it.

3. Removed both coils negative and positive wires and checked for resistance to the ht lead.

4. Gave the points a quick clean in sittue, sand paper then ran a bit of card through it.

5. Checked continuity at the points.

Any my help or advice would be greatly appreciated.

regards
steve
 
Allways do a compression test first it should be 70psi or over and even within 5%. Are you checking spark with a spark gap tester? It must jump a open air gap of at least 1/4 inch on both plug wires. What color are the coils and are there any cracks in the plastic coating? Did you set the points as close to .020 as possible? It could be several things I see 1979 as a breakerless ignition? That being a Belgium model may be different. It looks like the 1981 parts diagrams shows your type of design.
 
kimcrwbr1 said:
Allways do a compression test first it should be 70psi or over and even within 5%. Are you checking spark with a spark gap tester? It must jump a open air gap of at least 1/4 inch on both plug wires. What color are the coils and are there any cracks in the plastic coating? Did you set the points as close to .020 as possible? It could be several things I see 1979 as a breakerless ignition? That being a Belgium model may be different. It looks like the 1981 parts diagrams shows your type of design.
Click to expand...

Thanks for the reply, I will do a compression test when I get a tester but if there is no spark compression is irrelevant, I will look at setting the points tonight, has anyone got any tips for doing this, cam positions etc
 
You must determine if the motor is worth spending time and money on compression is allways the first step. Do you have pics of the points plate? If the compression is acceptable just get new points and condensers and a new head gasket. Use OEM points and condensers for best results the package should say BRP on the package. Line the rubbing part of the points to the woodruff key on the cam and set the points exactly .020 and tighten the flywheel nut to spec. If it fails to get spark still just replace the coils. After you have good compression and spark then you can focus on fuel.
 
kimcrwbr1 said:
You must determine if the motor is worth spending time and money on compression is allways the first step. Do you have pics of the points plate? If the compression is acceptable just get new points and condensers and a new head gasket. Use OEM points and condensers for best results the package should say BRP on the package. Line the rubbing part of the points to the woodruff key on the cam and set the points exactly .020 and tighten the flywheel nut to spec. If it fails to get spark still just replace the coils. After you have good compression and spark then you can focus on fuel.
Click to expand...

I have switched the coils and condensers over if either of them were at fault the fault i.e. No spark would have changed if the fault lay with condenser or coil, would it not?
 
Bulldogste said:
I have switched the coils and condensers over if either of them were at fault the fault i.e. No spark would have changed if the fault lay with condenser or coil, would it not?
Click to expand...

You would think so, but stranger things have happened. Go through the checklist above and see if you may have missed something. Gotta start someplace or we're at a loss to help.
 
Those magnetos are elegantly simple and used for nearly 40 years on OMC products.---------Very good and reliable once done properly.------------Did you have the maneto plate off when coils were switched ?----------Sure the wire is properly installed in the coil ?
 
Once again what color are the coils? possibly new coils were installed wrong? As racer said you must pull the plate and then take a pic of the bottom so you get it back together correct then fully screw the wires into the coils and slide the boot up tight. if the boot is split get new ones you could be losing spark there?
 
The coils are are green and there is continuity between both coils and ht leads about I suspect no brake in the leads
 
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This thing isn't starting to snap me that's everything from the working side been swapped over to the bad side coil, points, condenser and still no spark Iv set the points rechecked the ht lead showing resistance just under 4 ohms from from the coil to the ht lead on both sides wtf grrrrrrr
 
Go ahead and ----google----universal magneto------There will be more information on this simple device for you to be able to diagnose it.
 

Air gap for the coils is real important. You can test the condensers with a 1.5 volt AAA battery and a volt meter what you do is charge the condenser and then quickly put your volt meter on it and watch the capacitor discharge. The way I do it is hold the battery neg with the black leadon the cap housing and put the red lead in the lug on the wire and then touch the lug to batt pos it should read 1.5v or there about then just pull the wire off the batt and watch the condenser discharge. If the condensers are the same and the points are making good contact and the air gap is good for the flywheel magnets then the coils could be faulty. none of the wires on the coil should be shorted to the coil laminate. both the primary and secondary windings are connected to the coil ground wire and not the core.
 
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