Logo
FULL SITE MENU

Need help bringing a Johnson 20R273A back to life

M

Mike from Atlanta

Regular Contributor
I recently bought a non-running 1973 Johnson 20 HP (20R73A). I have started the work of getting it running but I am new to outboards and I have a bunch of questions. I’m a fairly experienced shade tree motorcycle and small engine mechanic but I have never worked on outboards. I just bought my first boat (1987 MonArk 1448 aluminum flat bottom jon) then bought the this outboard on the cheap to push it. I enjoy tinkering with anything with a motor so hopefully I can get this thing running without spending a fortune.

What I have done so far:

  1. Bought a repair manual. Wasn’t sure which one to get. Ended up buying a vintage factory manual published in 1973 on Ebay. All black and white pictures. Pretty cool.
  2. Built an outboard stand. I’ve got a plastic trash can for a test tank.
  3. Bought new fuel tank, fuel line and fittings.
  4. Tested compression. 102 PSI upper cylinder/99 PSI lower cylinder cold
  5. Tested spark. Pulled both spark plugs out, connected them to the plug wires, layed them on the engine block and pulled the rope. Bright, strong looking spark on both plugs easily visible during daylight.
  6. Mixed up some 50:1 premix fuel. Primed the bulb till firm (not sure what this is supposed to feel like). Pulled out the choke which appears to be operating correctly. Pulled on the recoil starter 10-15 times. Nothing. Not even a stutter. Pulled the spark plugs and they were wet. Used compressed air to dry the plugs and blow out the combustion chambers. Pulled the rope a few more times. Nothing. Dried the plugs chambers again.
  7. Put some premix in a spray bottle and misted it into the carburetor. Pulled the starter and this time it did stutter and back fire a bit but no continuous running. attempted this a couple of times with the same result.
  8. Removed the carb. Pulled the float bowl and it looks pretty clean. Like it wasn’t stored with fuel in it. While attempting to remove the high speed jet (manual calls it an orifice plug) I boogered up the screwdriver slot on the jet pretty badly. I used a grinder to make a narrow screwdriver to fit in the hole but I guess it didn’t fit well enough. Ended up having to remove it with a screw extractor. This arrangement of the main jet is unlike any carb I’ve ever worked on. Thought it best to stop the disassembly until I get the new carb rebuild kit in hand.

Questions:

  1. Does anyone know if the carb rebuild kit (marineengine.com part# 0396701) comes with a new high speed jet? It doesn’t look like it does, but every other carb kit I’ve ever bought for motorcycles and small engine stuff came with all new jets.
  2. If it doesn’t come with the kit, is $30.50 (marineengine.com part #0319534) average price for a new one? I’m used to jets costing $3-$6. Is there anywhere to get one cheaper?
  3. Looked up the special screwdriver (OMC 317002) for the high speed jet and they cost $30-$45. For a screwdriver. Ouch. Is there anywhere to find one for less? Or should I just try again at making one. May be easier to make one that fits the slot tightly if I have a new jet in hand.
  4. When I took the float bowl off there was gas in it. I don't know if this is because the fuel pump is doing it's job or if I pushed it in there with the priming bulb on the fuel line. Is there a way to test the fuel pump?

Thanks in advance for any suggestions. Hopefully it runs after the carb rebuild. If not maybe I’ll look at the ignition timing unless anyone can think of something else I should check. I’ve never worked on a points-type ignition so it should be interesting.
 
Hi Mike. I will start with the jet. Can probably get one from me, but I have to find the correct size for your outboard. The screwdriver you can make yourself, just grind slowly and carefully the exact size for the bore and the jet slit. Use a good quality steel and don't get it too hot as to loose the temper.
More later, wife calling to go to bed....treats me so very kind.
 
1. Carb kit does not include the orifice plug.

2. Old saying goes that a boat is a hole in the water that you dump money into. Sorry 'bout that. I guess you can try looking around for one. Try the Antique Outboard Club's classified ads pages. www.aomci.org

3. Find a phillips screwdriver with a 3/16" shank and cut the end off and grind to flats to fit the orifice slot. It is very important that the sides of the blade be parallel. A tapered blade will spread the slot in the orifice, making it tighter as you exert force. It doesn't have to be overly tight anyhow.

4. The fuel pump has nothing to do with starting the motor. It only takes over to keep the carb full after it is running. If the carb was filled via the primer, it should start.

5. Testing spark by laying plugs on head is next to worthless. It needs to throw a 1/4' open spark or better.

6. The '73 has the OMC Lo Tension Magneto. Some people hate them, but they really aren't that bad. Most importantly is the breaker points need to be clean and properly gapped. By clean, I mean clean.
 
Last edited:
Thanks for the replies I wasn't expecting such a quick response!

Timguy- I'm in the same boat...I was rushing to finish my post so as to get to bed and stay in the good graces of my wife. If you have one of these jets I'd love to take it off your hands. The parts diagram on Marineengine.com calls it "Orifice plug, High speed, 67D". Don't know if that helps. I'm not familiar with how these are sized. And I will admit the screwdriver I ground on my first attempt was a cheapy that came with my chainsaw. Will use a better one next time.

Fdrgator- I had heard that B.O.A.T, stands for Break Out Another Thousand. That's why I avoided them for so many years. Wasted my dollars on motorcycles instead. But my bike ('04 Kawasaki KLR650 with 82,000 miles) suffered catastrophic engine failure about 2 weeks before my baby boy was born in October. I took that as a sign it was time to make a change to something that will accommodate having a little guy in tow. Sold the bike for parts which pretty much covered the boat and trailer.

-Thanks for the tip! Cutting off a phillips and grinding the shank to fit is sheer genius I'll do that for sure. Once I have a new jet in hand I should be able to carefully grind it to match the profile of the slot. And I will avoid the taper.

-How should I test the spark? The method I used is the only one I know of but I'm open to suggestions if there is a better way.
 
The points gap is 20 thou.See if you can get a look at the coils,if they look tatty,you will get a bad spark.
When you do the carb,make sure you clean the fuel cut of orifice that the cut off pin fits in.
With the bowl off,(with the carb off the engine)turn the carb upside down and check the float level.It is supposed to be parallel to the body.(this gives the fuel level in the bowl.To correct the level,you bend the clip that holds the cut off pin (Gently)
You can't beat stripping all the valves out and cleaning the carb with carb cleaner,then blowing it dry with an air line.
If the motor has sat for a while,the old two stroke oil and fuel could have evaporated.This leaves gummy deposits where you wouldn't imagine.
If you have the flywheel off,clean and set the points.If you change the coils,change the HT leads at the same time.
Be a good idea to check the impeller,they perish if they have been left for a while.Drop the gearbox oil and replace it.I use molyslip gear additive in all my outboards,they run quiet and shift easily.
Bit of a list I know,but if you like fiddling with engines,you should be in your element.Haha.
 
There are many kinds of spark checkers. Or you can make your own. Down to bare basics, all you need is something to stick into the spark plug boot and hold it 1/4" away from a ground. Think a #2 phillips again, with a 1/4 shank this time. Stick it in the boot, hang onto the plastic handle. and hold it near a head bolt. How cheap can it get?
 
Valvebounce-
I am definitely going to completely disassemble the carb, soak it overnight in carb cleaner, clean all the orifices, blow it out and reassemble with new parts. Even though the carb looks pretty clean I want to rule it out as the cause of my problems.

If the carb rebuild doesn't fix it I'll start looking at the points, coils and ignition timing. I like to fix one thing at a time then test the motor to help narrow down what the actual problem is.

After I get it running I'll go through and do all the maintenance stuff like the impeller and gear oil, plug wires etc. I don't trust rubber parts that have been sitting that long and I want to be able to trust this thing once I get out on the water. My boat isn't big but I don't think it would be much fun to paddle!
 
I tend to do one job at a time and then test it,after running motocross bikes I find it less disappointing than finding the day ruined by not having a procedure.
I've just changed the coils on a 1963 18hp Evinrude . And changed the prop for a 9 x 9.
The prop is where you tune your motor for that window you require on an outboard .
Smaller pitch and dia=more pickup and less topspeed,Too big a prop,boat won't plane and the fuel usage goes up.
 
Per fdrgator's advice I started trying various methods of testing if the spark would jump a 1/4" gap. Proved to be a bit difficult to do by myself while operating the pull starter. So I went to the local parts store and found a perfect tool for the job for about $10 (tried to attach a pic of the tool but couldn't figure out how to do that). Didn't get spark for the 1/4" gap or even smaller on either plug wire. I suspected the tool might be faulty so I tried it on a little Mercury 3.3 HP that I know runs like a top. On that motor I did get the spark to jump the gap. The spark tester works just fine. Looks like I have and ignition problem on the Johnson. I get spark by grounding the plug on the head but not a strong enough spark to jump the gap. I'll start reading the manual about how the ignition system works and how to troubleshoot it. Any advice as to where I should start?
 
My boy was riding in the boat at 6 months, so we had better get going here. Weak spark could be points or coils. Sounds like you got a good idea going, bikes can kill you alot easier than boats, and you can't bring that little guy on the bike anyway. I had a '71 H2 Kawie, talk about a dead man's bike. Sold it to a guy that got lucky, he only ended up in a wheelchair for life. I haven't been back to the shop to look for the jet, but I probably will have one. If the coils have been replaced they are probably okay, you can see if the paint is scratched around the screws or perhaps they are set too close and rubbing the flywheel, Joe Reeves has a good idea on how to set these coils. Most mechanics mess up the screws too, you can certainly tell if they have been worked on.
 
According to the parts book this has the " low tension " magneto.----Driver coil and 2 external ignition coils.----Test the driver coil.---Make sure points are absolutely clean.
 
The way they insulated the coils years ago wasn't as good as it is now.
I have a 6hp evinrude fisherman and an 18p evinrude,both needed coils when I bought them as non runners.
I find changing the coils gives you the chance to set your ignition up perfectly.
Taking the points out and checking the connnections gives you piece of mind on the water.
Take a little time and get your points set dead right,checking and rechecking .
 
Agreed , but this motor is shown with a different magneto.----The driver coil did not suffer from the same fate.------The 6 HP fisherman never used this " low tension " style magneto.
 
Sounds like testing the coils might be a good idea.Could save a bit of expense maybe.
I seem to remember,the coils on the fisherman and the 18hp were the same.
The 6hp is a '73 model,and the 18hp is a '63.
So what is the difference in an LT magneto,is it connected a battery?
 
The parts book on this site shows the 73 20 HP with a low tension magneto.------Not the same magneto as the 73 model 6 HP !----And no there is no battery involved with the " low tension magneto "
 
Oh, that's right, Racer! This was the first year, but only on certain horsepowers. These coils were less likely to fail. So probably have to focus on the points, and final (external) coils. I was thinking '72. General Motors came out with HEI in '73 also, but only very limited on some models.........enter a new age. HEI came full out for GM the next year and for the '75 models.
Note: I have tried repairing some of the old high tension coils with "burn through", but with limited success. It seems once they start to arc to the stator....or whatever.....the windings become compromised. They have begun to arc internally as well, in many cases. So they really can't be trusted. Don't know about you, but I have saved "boxes" of those cracked, burned coils. Probably should knock them apart and cash out the copper.
 
Last edited:
Thanks again for all of the help everyone!

Timguy- My boy is 4.5 months old now so with any luck getting this motor running I'll be able to take him for his first boat ride at six months too. And it'll be May by then so definitely good and warm here in Georgia. And my old neighbor was into restoring the old Kawi 2 stroke street bikes. He let me ride his H2 once. Once was enough. That thing was scary fast. A widowmaker for sure.

My plan is to dig into the ignition system this weekend. It's harder for me to get a day in the workshop now that we have a baby in the house. I've been reading the manual and doing some online research about troubleshooting the magneto ignition. Found a series of Youtube videos where a guy walks through the process of testing the coils and plug wires, cleaning the points and setting the gap, and setting the timing. I believe he does it on the 6 hp motor so it may not be completely applicable, but between that and the manual hopefully I can figure it out. If anyone knows of a good video or online tutorial please let me know.

Current plan is to dig into the ignition system this weekend. The troubleshooting procedure in the manual calls for the use of an ignition analyzer, which I obviously don't have.

Racerone- I'll test the driver coil and clean/gap the points. That procedure is described in the manual. Hopefully I can narrow down the cause of the weak spark and then order any ignition parts if needed as well as the carb rebuild kit.
 
Dug into the ignition system yesterday. Removed the flywheel and found that the parts on my armature plate do not match the parts diagram in my repair manual or on the online parts diagram on Marineengine.com.

-What the manual and website show that I should have: 1 driver coil, 2 condensors and 2 breaker points.

-What I actually have: 2 coils, 2 condensors and 2 breaker points.

Any idea how this might happen? The stern bracket assembly on my motor isn't in great shape ( broken clamp screw and non-stock tilting shaft bolt). I wonder if the stern bracket assembly (with motor identification plate) may have been swapped off of a different motor at some point? Or maybe the whole ignition switched out? In terms of general appearance, the coils appear to be old parts and are green, the condensers have a bit of light rust on them, one breaker point is shiny and new looking while the other has a bit of light rust. The plug wires are non-matching and missing the plug boots but appear intact with no cuts or breaks in the casing.

While I was in there I attempted to test the coils based on a Youtube tutorial I found from a channel called ThisOldOutboard. I'm not especially skilled with the use of my digital multimeter but I gave it a shot. I set the meter to the 200 ohms setting (mine doesn't have a continuity setting) and tested the primary coils, secondary coils and the spark plug wires. the following are my results:

front rear
Primary coil 1.3 1.5
Secondary coil Infinity (6.96 @ 20k) Infinity (6.96 @ 20k)
plug wire 0.6 0.6


When I got the infinity reading on both secondary coils at the 200 ohm setting, I started adjusting the settings on my multimeter. When I used the 20k ohms setting I got a reading of 6.96 on both secondary coils.

Can anyone help me interpret these findings? Are my coils ok? If so should I just reassemble all the components, clean and gap the points and see if I have strong spark?
 
Perhaps early 73 production.-----Perhaps transom bracket was swapped out.-----Perhaps an earlier powerhead istalled.----Does serial # on the block match serial # on the bracket ?
 
Racerone- Great idea i hadn't thought of that. I did a bit of looking around and some quick online research about where to find the serial numbers on the block but couldn't figure it out. Found several sets of numbers on the motor but none in the same format as the serial number in ther ID tag. Any suggestions about where to look?
 
Perhaps it got in the hands of one of those Low-Tension haters, and they retrofitted it to the OMC Universal Magneto. If that is the case, simply go by the tried and true procedure used for the previous 20 years or so.
 
Just realized that my post with the coil test numbers got reformatted and is a bit confusing. Here's the numbers again hopefully in a better format.

Front- Primary coil-1.3 Secondary coil- Infinity (6.96 @20k setting) plug wire-0.6

Rear- Primary coil- 1.5 Secondary coil- Infinity (6.96 @20k setting) plug wire- 0.6

Assuming I need to use the test procedure for the older ignition system, can anyone help interpret these numbers? Are the coils good?
 
I test coils with a MERC-O-TRONIC magneto analyzer.-------They are cheap so often no point in testing them.----If points are clean and condensers test good you should have good spark.----If not you need new coils.
 
Resistance checks for the OMC Universal coils vary according to manufacturer. As a rule of thumb, I always say primary "About an Ohm", and secondary "A few k-Ohms". I call a "few" to be around four to seven k-Ohms. Yours sound in the ball park if I understand what you are saying.
 
fdrgator- Thanks. If it looks like the coils are good, and I don't have a way to test the condenser, I think I'll clean/gap the points then reassemble to see if I have strong spark. If that doesn't work then I'll start throwing parts at it. I looked up the parts diagram for the previous year (1972) and that part looks like the ones I have. Bonus is that they're also about half the cost ($20 apiece instead of $40 apiece). At that price it looks like I could rebuild the entire ignition system for $60-$70 Including coils, condensers and points.
 
If your points aren't burnt,and are not heavily pitted,your condensors should be ok.For the price of them,I'd get new ones.

(condensors)
 
You can charge the condensers with a brief tap from a small 10,000 volt oil furnace ignition coil or similar. Of course have them on your bench. I wait a few seconds then arc the condensor's wire to the condenser case. If hot lightning like arc occurs, your condenser passes its test.
 
Back
Top