67 johnson 20hp problems

[67-69johnman]

let me start by saying im new here. first time forum member here.
but lets get right down to it. Im working on a 67 johnson 20hp outboard shortshaft tiller. i recently got this fine example from a rather questionable source. I've recently gone through and cleaned the carburetor(carb cleaner, oriface cleaners to the best of my ability) and put a new float and needle in. The thing runs like a dream in the bucket. Pushes water fine and revs fine my tiny tach puts one plug wire at around 2800 rpm, which it says under the hood its 20hp at 4500 rpm. seems about right.

NOW

The problem im faced with is during our first on-the-water test run it was like night and day. With the boat in front of that motor i experienced slight surging. It would not reach full rpm on a regular basis. in fact almost never. under load, the motor would occasionally take off and act right (for times under 1 sec)


Down but not out, Im planning on cleaning the carb again. and currently i've pulled the flywheel with a puller and am looking at the points




Any suggestions?
Am I heading in the right direction?

 

[HighTrim]

Re: 67 johnson 20hp problems

Have you checked spark? Is it jumping a good 1/4" gap on an inline tester with a bright blue ZAP!!?

What about compression? Always start with these basics.

 

[67-69johnman]

Re: 67 johnson 20hp problems

Warm. Got spark. But on a tester, that I will have to find out. Do you know of any way to make one?

Spark testers, compression tester these are tools I need to aquire

By the way. The compression feels good on the cord.
Good stuff. Any other tips for a new outboard maintenance enthusiast?

 

[kfa4303]

Re: 67 johnson 20hp problems

HI 67. I have a 66 20 hp that runs great. I agree with High Trim, I think you may be having and electrical issue. It's not uncommon for these old motors to start and run surprisingly well on only one cylinder. If the motor still has original coils one, or both are almost certainly bad. You may also be dropping a coil once the motor heats up and you get underway. The fact that is starts and idles in a tank is good and means that the compression is probably fine, but you can test it if you like. Here are some great links to get you started. Give them a read and holler back. You can get any parts you may need right here at iboats. Generally speaking you can rebuild the carb, ignition, waterpump and more for less than $150.


http://www.duckworksmagazine.com/07/columns/max/index1.htm

http://forums.iboats.com/showthread.php?t=158086

http://www.outboard-boat-motor-repa...on 3 HP 1952-1967 Ignition System Tune-up.htm

http://www.marineengine.com/parts/v...ntage-evinrude-johnson/382088/38208800001.htm

http://www.iboats.com/Johnson-Outbo...3432658--**********.130751073--view_id.271265

 

[67-69johnman]

Re: 67 johnson 20hp problems

if you say since im running ok then im inclined to believe you when you say the compression is probably good.
and due to the fact that i dont have the equipment to test that ill continue onward.
i set the plug gap at 30 thousandths and set the point gap 20 thousandths pulled the cord (thats getting old so im hooking up my battery) and ZOOM apparently there was just a little gas left.

not confident this solved my problem but we wont know until sunday when we can get out on the water.



this has been an impressive find for 50 bucks though. after a new impeller, wear plate, (housing looks good) lower gear case seal kit. part of a carb kit, and added a starter and solenoid, so far. runs ok. like i said not confident that solved my problemo but.




after setting the points and plugs and ASSUMING the compression is ok is there anything else you can suggest?

common problems?
what is the torque on the flywheel nut?

 

[67-69johnman]

Re: 67 johnson 20hp problems

ONE MORE THING.
after reading the first link (about 2 seconds into the read) "syncronize the throttle butterfly with the magneto"
the little plastic wheel on the throttle linkage DOES have some slight grooves worn in it. i would say at the deepest 1/64th of an inch in depth would this cause this much of a problem on my acceleration under load?

 

[F_R]

Re: 67 johnson 20hp problems

Throttle sync will affect the way it runs at about quarter throttle or less, but no effect on full throttle (unless the linkage is totally screwed up)

Your description certainly points to one cylinder cutting in and out. When not firing, it is slow. When it fires, you get that burst of speed. That, my friend, is an ignition problem. You gotta diagnose it from there, nobody can do it from here. Can be points, condenser, coil, plug wire, spark plug. If the coils are cracked, they are shot----period. OR it can be gettng water into a cylinder.

EDIT: Flywheel nut torque is 40-45 foot pounds. Extremely important!!!!

 

[kfa4303]

Re: 67 johnson 20hp problems

I agree with F_R. Here's a great link that can walk you through an entire ignition rebuild. You can get any parts you may need for the job right here at iboats too. Tune up kits with points and condensers are about $20 as are coils. I would also suggest you get some new/fresh 7 mm COPPER core spark plug wires while you're at it. They're often overlooked, but can make a world of difference. Just be sure you twist the new wires onto the coils rather than just poking them onto the coils posts.


http://www.outboard-boat-motor-repa...on 3 HP 1952-1967 Ignition System Tune-up.htm

http://www.duckworksmagazine.com/07/columns/max/index1.htm

 

[67-69johnman]

Re: 67 johnson 20hp problems

Very helpful links. After the napa tune up kit and two new coils. It zapped 3/8 of an inch on the spark tester. However my oversight of the simple things dooms me at times. Being the local auto parts store had no new 7mm copper core plug wire. I opted to reuse the old ones ace removing half an inch of wire to put on the new coils this revealed a cut in wire number 2 causing occasional grounding. Some shrink wrap on the wire and ZOOM . Kfa f_r your expertise have served me well thank you!

 

[kfa4303]

Re: 67 johnson 20hp problems

awesome! vroom-vroom! Happy boating.