Mystery Johnson

[Sturgell]

Had a buddy bring me a boat and motor to get tuned up for fishing season and I am having hell, generally I am pretty slick on engines but this thing has me stumped. I am pretty sure it has an issue with the points (possibly only getting fire to one cylinder) but they are under the flywheel with no inspection cover so I need to pull it off with a puller. The engine refuses to idle at low speed and it is gutless on the top end only pulling a 14' flat bottom jonboat to 6-8 mph. The upper mixture screw has little effect on the idle quality, all ports and passages inside the carb are clean and clear, no flooding due to the float. Any ideas on the year? The serial tag is on the transom clamp but there is not a model number to be found anywhere. It has a fiberglass cover and is marked as 18 hp.

Here are some pics

 

[KB1]

Re: Mystery Johnson

18 or a 20 looks like to me. I'd say you are correct on just needing TLC!! Iggy stuff and make sure fuel lines and pump are good to go, water pump service, can't see prop, but from looks of rest, I'd say it's pr'ly good too!!

Better get that bolt back in where the neg. wire is loose. Definitely don't want that mount to break!!!

ENJOY w/ bud's use of helm and you're use of fish. pole!!!

 

[Sturgell]

Re: Mystery Johnson

18 or a 20 looks like to me. I'd say you are correct on just needing TLC!! Iggy stuff and make sure fuel lines and pump are good to go, water pump service, can't see prop, but from looks of rest, I'd say it's pr'ly good too!!

Better get that bolt back in where the neg. wire is loose. Definitely don't want that mount to break!!!

ENJOY w/ bud's use of helm and you're use of fish. pole!!!

I only had that out to get the carb off, I take pics of everything now after having fits with linkages and the way they go back together.

I am kind of afraid someone has been in it before me and may have already buggered it up.

 

[F_R]

Re: Mystery Johnson

18 or a 20 looks like to me. I'd say you are correct on just needing TLC!! Iggy stuff and make sure fuel lines and pump are good to go, water pump service, can't see prop, but from looks of rest, I'd say it's pr'ly good too!!

Better get that bolt back in where the neg. wire is loose. Definitely don't want that mount to break!!!

ENJOY w/ bud's use of helm and you're use of fish. pole!!!

It is a 1964-ish. 1965 was the last 18hp. So, what is the serial number anyway? What is the number on that round disc behind the fuel pump?

You need to get that flywheel off. It is running on one cylinder.

 

[Sturgell]

Re: Mystery Johnson

It is a 1964-ish. 1965 was the last 18hp. So, what is the serial number anyway? What is the number on that round disc behind the fuel pump?

You need to get that flywheel off. It is running on one cylinder.

It was 70 degrees today and tomorrow is calling for 12-22 inches of snow here in tropical OK, so the mechanic in me is on hiatus. I figured it was as I have never found a neglected 2 smoke motor that needed more than a little tune up to run like a top and the points is the only thing I haven't gone over on this engine.

SN 10022-10689 and J2492120

 

[JB]

Re: Mystery Johnson

Your pix are far too big. Please downsize them to 640X480 or smaller.

 

[Sturgell]

Re: Mystery Johnson

Your pix are far too big. Please downsize them to 640X480 or smaller.

But then you can't see the little grease specks as good.

 

[1946Zephyr]

Re: Mystery Johnson

It is a 1964-ish. 1965 was the last 18hp. So, what is the serial number anyway? What is the number on that round disc behind the fuel pump?

You need to get that flywheel off. It is running on one cylinder.

I second that. It sounds an awful lot like it's runing on one cylinder to me too. You can tell by the spark plugs when you remove them and see which one has been burning and which one still has wet fuel on it.

Start first by checking the connectionn at the spark plug boot. I have seen may of these get rusty and lose contact.

Then pull the flywheel and clean and adjust the points. While you're there, make sure the insulation on the coils aren't cracked. Chances are, this is your problem, but do the free checks first.

The size of the photos are not the issue at hand here. A motor running on one cylinder is. I can see the photos just fine. iBoats will only allow you to upload a tiny file anyhow.

 

[Sturgell]

Re: Mystery Johnson

I second that. It sounds an awful lot like it's runing on one cylinder to me too. You can tell by the spark plugs when you remove them and see which one has been burning and which one still has wet fuel on it.

Start first by checking the connectionn at the spark plug boot. I have seen may of these get rusty and lose contact.

Then pull the flywheel and clean and adjust the points. While you're there, make sure the insulation on the coils aren't cracked. Chances are, this is your problem, but do the free checks first.

The size of the photos are not the issue at hand here. A motor running on one cylinder is. I can see the photos just fine. iBoats will only allow you to upload a tiny file anyhow.

I only link them from photobucket so I really didn't see what the problem was but whatever. Are you saying it is likely that the coil is cracked?

 

[1946Zephyr]

Re: Mystery Johnson

I only link them from photobucket so I really didn't see what the problem was but whatever. Are you saying it is likely that the coil is cracked?

Yes, this is a common thing with these, but is not neccesarily the problem. It could be as minute as a bad connection in your spark plug boot or dirty points. These are the "free checks " to start with, but when you get the flywheel off, you'll easily be able to see the condition of tthe coils. If you do see they are cracked, then it would be wise to replace them, because "antique coils" can and will leave you stranded.

 

[cougar1985]

Re: Mystery Johnson

i would bet on the coils being shot on a 18 that old for sure.new coils,points ,and carb rebuild would go a long way to peping her up as long as you have healthy compression to begin with.

 

[Sturgell]

Re: Mystery Johnson

Well I pulled the flywheel and to my surprise both coils were BRAND NEW looking, as were both sets of points but both condenser wires were worn through the insulation grounding out to the inside of the flywheel. I am going to replace them both and see where that gets me.

 

[1946Zephyr]

Re: Mystery Johnson

Yea, that is a nice surprise isn't it? Opening up a flywheel on an old motor and finding new coils, is almost like opening up a gift and getting something you really wanted.

I believe those condensors will fix your problem. You'll want to be careful how you reconnect the wires so they are scrunched down out of the way of moving parts, unlike the last guy did.

 

[Sturgell]

Re: Mystery Johnson

Yea, that is a nice surprise isn't it? Opening up a flywheel on an old motor and finding new coils, is almost like opening up a gift and getting something you really wanted.

I believe those condensors will fix your problem. You'll want to be careful how you reconnect the wires so they are scrunched down out of the way of moving parts, unlike the last guy did.

Yeah if they are as long as the last ones I am going to shorten them and solder new ends on them.

 

[Sturgell]

Re: Mystery Johnson

Nice surprise when I lifted her skirt.

EDIT: Pic too big. 640X480 is max.

 

[jrs_diesel]

Re: Mystery Johnson

Looks about identical to my 72 6 HP when I popped the flywheel off. I had my wife help me hold the flywheel still while I worked the flywheel puller. Once it was loose and off she even commented on how clean it looked

 

[Sturgell]

Re: Mystery Johnson

I do have a question though, Napa lists 2 different condensers for Johnson 18 hp's. My question is what is the difference between the two functionality wise?

 

[kbait]

Re: Mystery Johnson

Just get the shorter ones. I believe way back when they had taller ones. Don't bother splicing new ends to shorten wire.. Just route it down and 'in' over the points, and not in the flywheel's way. The guy that put the new coils in didn't do that! haha. And clean the points up shiny with a file and set at .020, and scrutinize the plug wires. You should get great spark, and full speed!

 

[Sturgell]

Re: Mystery Johnson

Just get the shorter ones. I believe way back when they had taller ones. Don't bother splicing new ends to shorten wire.. Just route it down and 'in' over the points, and not in the flywheel's way. The guy that put the new coils in didn't do that! haha. And clean the points up shiny with a file and set at .020, and scrutinize the plug wires. You should get great spark, and full speed!

The plug wires are rough looking as well, looks like the guy who did the coils and points only did half the job.

 

[1946Zephyr]

Re: Mystery Johnson

The plug wires are rough looking as well, looks like the guy who did the coils and points only did half the job.

If the plug wires look good, then I usually re-use them, but I typically trim off a little, before I attach it to the new coil. It's hard to tell whether the last guy even did that, so it probably wouldn't be a bad idea to go ahead and change out the plug wires, while you have it apart. You'll want about 4 feet of it. If you want to check for sure, take a measurement of the old ones, but I believe 4 feet will do your motor about right and leave you a few extra inches.