1968 Johnson 55 runs only 20 minutes

M

motto

Recruit
Joined
Apr 15, 2012
Messages
2
I have a 68 Johnson 55 that has been sitting for 18 years.
The carbs gave been cleaned, new power pack, coil, plug wires and plugs.
The engine was overhaul just prior to being stored.
It wil run great for about 20 minutes, then starts to bog down..
It will only run at low speed and dies if you try to accelerate.
I hav removed the cap on the tank and squeezed the gas bulb to see if it
Is a fuel issue with no change. I would appreciate any advice.
 
BonairII

BonairII

Commander
Joined
Jun 7, 2011
Messages
2,727
Re: 1968 Johnson 55 runs only 20 minutes

You may want to hook up a timing light to the motor after it starts acting up, to see if your losing spark.
 
eavega

eavega

Lieutenant
Joined
Apr 29, 2008
Messages
1,377
Re: 1968 Johnson 55 runs only 20 minutes

20 minutes before bogging down definitely sounds like a heat-up related issue. If you shut off the motor and let it cool off, does it run well again for about 20 minutes or so? Definitely try the timing light, you may have something expanding a bit when the motor warms up and shorting out the spark on one of your cylinders. If you run it at night, you may even be able to see arcing somewhere.

Rgds
 
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