Johnson Diagnostic Help

[leonardbaker1]

Good Evening,

I have a 1973 Johnson tiller steer model# 20rl73
I was out boating 2 weeks ago on vacation. The motor ran fine for a day and then while under way at half to full throttle the engine kept backing down the RPM's.
I noted the following while on the water;

It ran at idle, initially rough but after time smoothed out.
It ran at anywhere over about 1/4 throttle better and faster with the choke pulled out.
After a day of rest the same think repeated itself, it ran for maybe 1 minute just fine then bogged down.

I came home and rebuilt the carb, replaced fuel pump, replaced fuel lines and spark plugs and ran it for a considerable time in a barrel at home at idle with occasional bursts to starting throttle and it was great.

Took it out to local lake to test high speed and it ran for about a minute then bogged down. I tried pumping fuel bulb but it had no effect. Limped in to boat ramp at idle which started out choppy and missing but by the time I got the boat on the trailer it had evened out.

I checked the plugs and they seem oily but I don't know if that is because it was idling for half an hour or if there is another problem. Both plugs looked essentially the same

I checked the spark with a spark tester and the spark appears fine but can not test at high speed.

I am wondering if it at some point is running on only one cylinder. I had a motor years ago with a bad cylinder and the performance is similar. It is running on both at home and at idle/shift speed. I disconnected each plug wire in turn and performance suffered.

Anyone have any advice as to what I should do next. I really like this older motor and it has run very well up to this poing, it is paired with a 1959 15' aluminum boat which is a very good match for our boating needs.

Thank you,
Lenny

 

[oldboat1]

Compression check?

Fuel contamination (water)?

 

[leonardbaker1]

compression 116 and 120 changed tanks hoses and gas

 

[oldboat1]

Use a timing gun to check for cylinder drop at speeds -- no flash, no spark. You may need to revisit carb cleaning -- full disassembly and soaking (I like lacquer thinner), use of a soft wire to clean every orifice, finish with carb spray using the plastic nozzle. Check a diagram to make sure assembly is correct (e.g., nozzle gasket if called for). High speed orifice needs to be squeaky clean (I don't like to remove them most of the time as they can be damaged). Idle passages at the top need to be opened up for soaking and poking.

Best guess from your description is that the high speed jet isn't completely clear.

 

[leonardbaker1]

i will check carb again. this model has it on the bottom and it is not adjustable. it looked clean when i took it off but i ran wire and sprayed carb cleaner and compressed air through it. looked completely clear with flashlight. could this cause the intermittent problem im having? never used a timing gun. i will read up on it but how could i check it at speed?

thanks

 

[lindy46]

Have you checked the ignition? Sounds like one cylinder is dropping out. May be a coil which drops when it gets warm. Motor will idle pretty good on one cylinder.

 

[leonardbaker1]

I have not checked the ignition. I have been looking online at components and if I understand correctly it could be charging coil, ignition coil, points, or condenser. I have found a tune up kit as well as charging and ignition coil. Any recommendations as to what to do first so as not to replace everything right off?

Thanks

 

[racerone]

Test first.----Does spark jump a gap of 5/16" with a snap you can hear, yes or no ?----Is the high speed jet that screws into the carburetor bowl behind the drain plug clean , yes or no ?----Water pump impeller checked ?----Thermostat checked ?

 

[leonardbaker1]

I dont have good hearing so cant hear it. I used spark tester from auto parts store and get what looks like a good spark at 5/16 gap running at home in a barrel YES. High speed jet is clean i rebuilt carb and it looks perfect YES water pump impeller checked and good YES . i dont know how to check thermostat NO

thanks

 

[racerone]

Top of the cylinder head.----3 wee screws hold the cover for thermostat.----Often stuck open or missing.

 

[leonardbaker1]

The thermostat is in placed and closed. I have tested thermostats for cars in hot water, should I do that on this one as well?

I also checked spark and compression again while I was working on it. Compression same as before which is fine and I had my wife watch spark gap while I cranked motor good spark at 3/8 gap

BTW I have found no tell tale on this motor. Was told a couple of years ago that there is not one. Can you tell me if that is right?

 

[lindy46]

Yes, test thermostat in hot water - should open at about 140 degrees F. There is no tell-tale - only the large blubber-hole on the back of the leg. I still think you have an ignition problem. Perhaps not apparent when running in a barrel at lower speeds. Could be as simple as an old spark plug wire arcing out - they do bend and flex when you go to high speed. Are the wires original? I'd have a look under the flywheel.

 

[leonardbaker1]

thanks, i did test snd it opened and closed multiple times like it should. not sure if the wires are origina i have only had it for about 3 years. l they look good but the whole motor is clean and good looking. i will look under the flywheel but not sure what to look for. would you advise a get a tune up kit begore i borrow the puller so that i can just replace the parts under the flywheel while i have it off? the kit is cheap. If you recommend it i can order other parts as well. only problem is that sometimes motor will run for long times without problem

 

[leonardbaker1]

I completed my checking out of the carb. All passages are clean float assembly functioning properly and bowl had fuel in it

 

[lindy46]

Pull the flywheel and check before you buy anything. Points may only need cleaning and setting. If they don't look burned, file them with a point file or emery cloth and CLEAN them with acetone. I cut up a business card and dip it in acetone and pull it through the points to clean. Then set to .020" when the rub block is at the high point on the cam. Put it back together and see how she runs. You'll need a torque wrench to torque the flywheel nut to 40-45 ft.lbs. If it still runs poorly, install new points and condensers. Oh, and new points also need cleaning with acetone. If that doesn't solve the problem, at least on your motor, the coils aren't under the flywheel and are easily replaced.

 

[leonardbaker1]

Ok, thanks for the guidance I will do that tomorrow.

 

[leonardbaker1]

Thank you, I will do that tomorrow.

 

[leonardbaker1]

I cleaned the points, they looked good but I used emery and acetone as recommended. They were set to the correct gap.

I MAY HAVE FOUND THE PROBLEM...

After putting the flywheel back on I started the motor up.

Ran fine at idle
I revved it up to about shift range rpm and when I backed down idle was choppy, similar to what I had on the water after the engine bogged down at full throttle.
I immediately pulled plugs. The top plug was wet and oily, the bottom was fine.
I cleaned it up and swapped upper for lower plug and attempted to start motor, would not start.

Pulled plugs again and asked my wife to look at them as I pulled starter cord.
No spark on top plug, hooked up spark tester and there was spark. Well as I was moving the spark plug cable around to get good look at spark in shadow area we determined that it would spark sometimes and not others. Spark plug cable seems a little loose and free moving in coil.

Did same checking with bottom plug... same results and also cable seemed to be not too well attached internally.

These cables are integrated into the coil so I cant replace them. I should let you know that before our vacation I did do a lot of manipulation with these cables what with new plugs, checking spark and so forth and may have moved them too much causing a problem inside the coil.

Seems that there may be a problem with both plug wires/coils that is positional.


I thought that I would order new coils and give it a try, your thoughts?

Thanks

 

[jimmbo]

The if you can induce an intermittent spark by wiggling the wire, or kill a good spark by by doing the same, it kinda points to questionable parts. Or poor grounds

 

[oldboat1]

Don't some of those coils come with unassembled plug wires? Guessing they attach to the coil by pressing the wire onto a spike in the coil housing. Spring clips would have a spike that contacts the wire core.

You might check the spring clips in the boots first to make sure the spikes are contacting the core wire(s). Also, rotating and pressing the wires into the coils might give you a secure connection.