1976 25hp Johnson ignition question

[hardwater fisherman]

This may help.

 

[F_R]

Universal (almost) way to determine. Rotate shaft to top dead center on one cylinder. The set of points that are just about to open are the ones for that cylinder.

 

[racerone]

edited

 

[Crosbyman]

As per FR's post above the points association to the respective cyl is easy to figure out

when the cyl is at the top position the points just starting to open are the ones for that cyl.... while the other one remain closed.. Easy..... see ....the cam lobe's thicker part pushing the points to open.

when the other cyl reaches TDC the alternate set of points will open up.



see utube on standard magneto as a guide

 

[racerone]

The magneto on the 1976 model 25 might be different than what is shown in the video above.-----The rear set ( starboard side ) points might open to fire the top cylinder via the other set of points.----Both set of points must be absolutely clean.

 

[Crosbyman]

utube is just a guide... to show points openning to fire the plugs

caps probably shot unless tested good with a high voltage source (home made or commercial apparatus)

m. Mohat test box works very well. cheap to build

https://wrcoutboards.org/wp-content/uploads/2020/04/Part1_Condenser_Construction_Failure_Modes.pdf

https://wrcoutboards.org/wp-content/uploads/2020/04/Part2_Condenser_Testers_And_Testing_Correctly.pdf

https://wrcoutboards.org/wp-content/uploads/2020/04/Part3_Sizing_Condensers_Correctly.pdf

https://wrcoutboards.org/wp-content/uploads/2020/04/Part4_Repairing_Broken_Condensers.pdf

 

[ct1762@gmail.com]

getting back to original ignition question: i suppose the ignition coils are the only difference on these from the smaller ones, thus the magneto charge coils are called "drivers". the ignition coils must be on these to magnify spark as opposed to a system without them. Never measured voltage at the plug wires with a driver system, but i suspect its over the normal 4-6k volts from a system without them (at idle) but maybe someone can chime in here?

 

[gmarshall43]

I'm back working on this motor and it is still breaking that woodruff key on the crank shaft. I'm getting good spark. Compression is good and I cleaned the carb. I also lapped the shaft and flywheel. It wants to start but it backfires first. The best way to describe it is that it pops and a large bubble comes up from the exhaust then tries to run for a few seconds. After a couple of times trying to start it, it back fires and the key breaks. I did get the OEM part for it. I tried to attach a video showing my latest effort but it was too large to send. Could the flywheel be the problem? Any other ideas?

 

[jimmbo]

What are you Torqueing the Flywheel Nut to? Over Torqueing can ruin the Flywheel, and could cause shearing of the Key

 

[F_R]

I don't have an answer to your woes, but here are a few tidbits of information.
Those keys should not be shearing. But they will if the parts are not right and assembled correctly. It may be true that friction holds the flywheel, not the key.

But the key positions the flywheel to the crankshaft. If the keyways are battered it will be difficult if not impossible to get it in the correct position. That affects the time that the magnets pass the driver coil. And that affects the time that the points break as related to the electrical charge in the driver. And that brings up the points cam. As the bulletin says, it is different than other motors, and more critical.

Back to the flywheel, the tapers must be smooth and true, and the hub must not be spread or cracked, and the shaft and flywheel must be clean and dry, and the nut must be torqued to 40-45 ft lbs. Some advocate lapping the taper, but I don't. And the keyways must not be battered. In short, a motor would not have left my shop unless all those conditions are met. Come-backs are expensive.

 

[jimmbo]

I don't have an answer to your woes, but here are a few tidbits of information.
Those keys should not be shearing. But they will if the parts are not right and assembled correctly. It may be true that friction holds the flywheel, not the key.

I remember looking at Key on our 63 40hp back in 74 when the Flywheel insisted on coming off after the Motor had been in for a Tuneup. Good thing there was a Recoil above. Anyway, Looking at the Flywheel which was a fair massive hunk of Metal, I can't see how that little key could really hold the Flywheel, except to keep it in Time, as you stated in your post

 

[racerone]

Food for thought ----Some years the flywheel key for a 9.9 is the exact same as the key for a 300 HP V-8 outboard.-----So I would say that FRICTION / LOCKING TAPERS drive the flywheel and not the key !!

 

[gmarshall43]

Thanks for all the replies. I was torquing the flywheel at 40 ft. lbs. I took a closer look at the flywheel and thought the inside was a bit scored. I attached pictures of it. Can you tell if this is a problem?

Gary

 

[racerone]

Did you read post #17 ???----Obvious to me why the key shears !!-----Get some grinding compound and lap those tapers.

 

[gmarshall43]

Yes I did read it and I did lap it the taper, twice and still looks like that.

 

[racerone]

You must get a good fit / contact.-----Simple as that.----No good as it is now !

 

[tootallofwa]

Hello all

I normally work on the smaller hp motors but I was asked to work on a 1976 25hp Johnson that has sat for many years and won't start. Needless to say the ignition is a little different then a smaller hp motor. There are two blue coils on the side of the motor that go to the plugs and there is one coil with two sets of points and two condensors under the flywheel. There isn't any spark on either plug. Can someone explain to me how this all works?

Gary

There are Multiple kill switches on most 2 stroke outboards. Among them are; to keep you from starting the motor when it is not in its lowered position and not in neutral and not at idle. then there are ones for runaway and for when you want to turn it off. Most of these conditions ground your points somehow to kill or keep you from starting your motor.

Any of these can stop it from starting so it is not necessarily your ignition system.

 

[flyingscott]

Replace the points and condensers with factory replacements. Those ignition are notorious for burning up condensors.