Still trying to get this old Johnson running

[jdwilliams1]

It is a 75HP Johnson and I was trying to fire it up yesterday it turns over and then after a couple seconds there is a loud pop...almost a backfire sound. I have put new plugs, compression is 85-80-85-85, has good gas

It has run recently so the previous owner said.

It is a Johnson Super Sea Horse, Electric, I think 75HP
V4S 15R
2385713

After a crank for awhile I get a loud backfire, smoke from the exhaust and it will not start. Would this be a timing issue possibly?

How would you proceed? I was told from the guy I bought it from that the motor did run, but he replaced the magneto and I am starting to wonder if that did not get back together the right way.

I was also told it also sounds like a sheared key but I have bought a new one and installed it and now I am trying to hook things back up but I am worried the magneto assembly may not be the right one since the previous owner put a new one on but I am not sure how to verify it is a bad one.

Please help.

Thanks to all you who are much smarter than I....I am getting more knowledgeable every day

 

[Daviet]

Re: Still trying to get this old Johnson running

Are you in fact getting good spark out of the mag to the plugs? Are the plug wires on the proper plug?

 

[jdwilliams1]

Re: Still trying to get this old Johnson running

Are you in fact getting good spark out of the mag to the plugs? Are the plug wires on the proper plug?

I do not get spark at the plugs with my tester at last check. My dad is concerned the mag is not for this boat as we cannot find two timing marks on the flywheel above the mag that the owners manual talks about

 

[Daviet]

Re: Still trying to get this old Johnson running

You should have a single black wire to the mag, disconnect it and recheck spark. The mag does not have to be timed to the engine to produce spark. You can produce spark with the mag on the bench just by spinning it. Get the mag working properly and then worry about timing it.
By the way, your engine is a 1963.

 

[jdwilliams1]

Re: Still trying to get this old Johnson running

You should have a single black wire to the mag, disconnect it and recheck spark. The mag does not have to be timed to the engine to produce spark. You can produce spark with the mag on the bench just by spinning it. Get the mag working properly and then worry about timing it.
By the way, your engine is a 1963.

Here is the motor we are speaking of, do I disconnect the black wire with the red tip? Oh, also, the guy I bought this motor off of, gave e the old magneto and had the one in the image already installed. There is a small rectangular box on the on in the middle image with the word CHERRY on it...that is not on the old magneto...what is that?

 

[Daviet]

Re: Still trying to get this old Johnson running

Dissconnect the blue one, it should be the wire that runs to the ign switch to shut the engine off.

 

[194269]

Re: Still trying to get this old Johnson running

That is a safty switch, It prevents you from starting the engine with too much throttle setting.

 

[Chris1956]

Re: Still trying to get this old Johnson running

Disconnect the black wire with the blue tip. That is the ign killer. Look under the "Cherry" safety switch for timing marks. There should be one on the pulley, and a matching one on the pulley base. They should align when the timing marks on the flywheel align with the marks on the block and pull starter.

 

[Chris1956]

Re: Still trying to get this old Johnson running

Make sure you set both sets of points to exactly .020"

 

[194269]

Re: Still trying to get this old Johnson running

I think there is only one set of points.

 

[jdwilliams1]

Re: Still trying to get this old Johnson running

ok, I think I have come across our first issue. I am posting images ...it appears there is a shear key in the flywheel above the magneto, well not sure what happened but the shaft that goes down into the magneto has worn through or actually chipped off where the shear key is. So if this was your mostor what would be your next plan of action? New magneto or I have another magneto assemply, can the shaft be removed from it or is it not worth the trouble?

How much would a new assembly for this cost including cables cap and magneto? Where would I find one?

 

[jdwilliams1]

Re: Still trying to get this old Johnson running

one more thing, it says I should be able to get a spark of about 1/4" on the mag but it is probably only half of that.

 

[Daviet]

Re: Still trying to get this old Johnson running

The cam that is broken is to open and close the points, it is seperate from the shaft. Go to the site below, pages 4 & 5, item #34.
Your best bet for a complete assembly would be a salvage yard, look in the "Top Secret File", there is a list of salvage yards listed there.
A mag in good shape should jump a 1/4" gap with no problems. Maybe you have a weak coil, points not set correctly.
http://www.marineengine.com/parts/v...ntage-evinrude-johnson/379275/37927500001.htm

 

[Chris1956]

Re: Still trying to get this old Johnson running

Or a bad condenser.

As Daviet said, just a slight spin of the pully will cause a real good spark snap, if the components are in descent shape.

The points are connected together, so one set will affect the other set. Make sure both are clean and gapped correctly.

 

[jdwilliams1]

Re: Still trying to get this old Johnson running

ok, I am getting pretty good spark now in the magneto after changing the cam on the flywheel shaft but now I have inconsistent spark at the plugs and have decided the wires need to be replaced at least so I have ordered new wires and will get back to you.

I appreciate everyones help and will get back to you soon.

 

[Daviet]

Re: Still trying to get this old Johnson running

Keep us posted. Remember to check the cap and rotor, either one can cause inconsistant spark to a plug.

 

[Chris1956]

Re: Still trying to get this old Johnson running

When my '59 Fat fifty overheated, the distributor shaft expanded just enough to crack the rotor. Carbon tracking caused the spark to short to ground sometimes. It was impossible to see the crack or carbon trail, but the spark became consistant after I replaced the rotor.

Not sure if this ocurs on your motor...

 

[jdwilliams1]

Re: Still trying to get this old Johnson running

UPDATE!!!!

Well the new plugs came today, I put them on and replaced the bad cam on the magneto and guess what it fired....and ran!!...for about 10 secs. Then re-fired ran for about 15 secs. Then it actually ran for about 30-40 secs and I turned it off with the key. It ran a few more times but now I cannot get it to fire so I suppose it is time to take a look at the carb?

Any thoughts? I have ran the battery down trying to get it to refire and it will not.

 

[nwcove]

Re: Still trying to get this old Johnson running

have you tried squeezing the primer bulb after it starts?