Topic: Johnson tn-28 power issues – Antique Outboard Motor Club,Inc

This topic has 29 replies, 10 voices, and was last updated 4 years ago by gjonz.

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March 24, 2020 at 4:14 pm #198233
Flambeau5
Participant
Hi guys, this is my first post on the forum here so bare with me… I bought this Johnson tn-28 about a year ago at auction, it was stuck, and needed full new ignition, water pump, and seals. I have so far done done ignition, water pump, and cleaned the lower unit up. I have yet to do the seals as I want to get it running well first. The motor will start only in gear at full throttle and is still very hard to start, when it does go it will rev down to the start position just enough to take it out of gear and let it warm up if the mag lever goes lower than start the motor dies. I can then put it in gear and rev it up but it has no power compared to my gale 5hp. It sounds like it is running on both cylinders. I have linked a video of it running. if I left something out let me know, any insight is much appreciated.

Thanks in advance

video
March 24, 2020 at 4:30 pm #198234
gjonz
Participant
There are two carbs on that motor. One is the big wheel on the recoil that adjusts the high speed. There is also a slow speed cab under the front of the power head by the tiller mount. It looks like a little L shaped bar. It should be between 3/4 and 1 1/2 open from gently seated. The high speed should be around #5 on the dial. (3/4 open from seated)

Set the high speed first for max rpm’s. Then the low speed.

Otherwise sounds like both cylinders are firing.

However it also could be low compression which is more involved.

Greg
March 24, 2020 at 5:00 pm #198244
crosbyman
Participant
Canada Member - 2 Years
lots of good info on the Poche family site

you probably need 2 leather seals in the primer pump one member in aomci sells them and will likely chime in…

http://www.pochefamily.org/outboard/CarbService.html

other sections on the Poche web site can help

make certain you find / clean the screen mesh filter and the check valve in the bottom

I have a nice TN27 sitting the the shed ready to fire up one of these days

you should go to boat info for all you need on the TN27

look at the URL in the red book picture…. if I post the link this site will zap it out so see URL in the picture

click the books on top… select Johnson …select red book great book for all oldies

Joining AOMCI has priviledges 🙂
March 24, 2020 at 5:35 pm #198256
Flambeau5
Participant
thanks for the replies, I will go check the compression, what would the symptoms of bad leather seals be? I followed the poche guide when I cleaned the carb yesterday and everything looked ok. I will report back with compression numbers.
March 24, 2020 at 5:53 pm #198264
Flambeau5
Participant
Compression is 68 on bottom 60 on top. When I had this motor apart to un-stick it I freed the rings and replaced the ones that broke
- This reply was modified 4 years, 1 month ago by Mumbles.
March 24, 2020 at 6:19 pm #198271
Buccaneer
Participant
US Member
Mine ran okay at 65 psi, even compression, but weren’t great low speed idlers.
With any luck your compression could come up a little after running a while.
My best idler had 70 psi.

Prepare to be boarded!
March 24, 2020 at 6:55 pm #198275
frankr
Participant
US Member
60 psi is low. On mine, the slow speed needle was best at 5/8. Yours may vary. Bad primer seals show up as slopping gas out of the primer plunger when you press it to prime. Yeah my Gale wedge-head would run circles around my TN. But my TN only had 60psi also. Did I mention that is low?

EDIT: Not sure, but it looks like your Slow/Start/Fast lever may be bent. Also, are you sure the points are set correctly? I noticed it slows down when you give it full throttle, which might be due to too much spark advance (points opening too far/soon)
- This reply was modified 4 years, 1 month ago by frankr.
March 24, 2020 at 9:11 pm #198296
Flambeau5
Participant
Ok, I know a mechanic down on fox lake has got a power head for this motor, when this whole Coronavirus has blown over I’ll make my way down there to see if I can buy it off him. Thanks for your help and suggestions. I’ll update this thread when I get it going well
March 25, 2020 at 1:26 am #198309
JOHN HOLBIK
Participant
I put hundreds of hours on those Tn2 7 and tn28s back when I was a guide at our fishing resort. Very very reliable motors troll like a dream but load up with gas pretty quick when your trolling a short burst of speed and all is well the other thing is the drive spring goes south if you start spinning the prop in sand.I have a 1962 Gale 5hp and it is about the same speed as a TN The CD12 5.5 Johnson seemed like a race horse compared to the TNs.
Your motor sounds to me like the slow speed circuit is plugged unscrew the slow speed needle that is the one on the bottom of the engine with the bent end then pump your primer
and flush it out. Set it to about a turn out and turn in slowly as you set for slow speed
Do not not be hasty to change power heads your compression will probably come up the more you use it I have seen them run fine on 50 lbs with 16 to 1 mix.
March 25, 2020 at 7:32 am #198311
crosbyman
Participant
Canada Member - 2 Years
Joining AOMCI has priviledges 🙂
- This reply was modified 4 years, 1 month ago by crosbyman.
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