1978 70 hp johnson

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B0939

Cadet
Joined
May 2, 2013
Messages
7
I can not achieve wot on my 1978 70 hp johnson. It wants to bog down when advanced. Help!!!
 
gm280

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,590
Re: 1978 70 hp johnson

Could be both the carb(s) and a timing problem. I'd clean the carb(s) first before adjusting any timing issues. Then try it out and if still bogging, timing would be the next fix. Are all cylinders firing? You can remove the spark plug wire to see if the RPMs change. If you remove a plug wire and nothing changes, that cylinder/plug/spark coil is dead. If all are firing correctly then you need to check the advance timing issues...but only after cleaning the carb(s) first. Make sure your fuel system (primer bulb and pump) are doing their job first too. JMHO though... :)
 
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shawn.54

Petty Officer 2nd Class
Joined
Jun 21, 2012
Messages
104
Re: 1978 70 hp johnson

i have a 78 75hp evinrude had same problem ideled without miss but had about a 9.9 at wot. carbs are realy touchy about dirt but also very simple to rebuild about $$20 each. be ready to replace fuel lines two of mine come apart when i unhooked

them. good luck

shawn
 
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B0939

Cadet
Joined
May 2, 2013
Messages
7
Re: 1978 70 hp johnson

Thanks for your input. I am rebuilding the carbs this weekend. I will take these steps when they are rebuilt. Can someone tell me why at times, after not being able to achieve wot, my 70 hp johnson will keep a smooth idle to my cove on the lake, then after a while after turning the motor off, i can achieve wot for a very short time then its back to cruise mode. Thoughts??
 
F

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: 1978 70 hp johnson

Before you do anything, make sure the throttle lever is advancing the timer all the way before fully opening the carburetor's throttle plates. Sticky timer bases are common and will cause bogging.
 
B

B0939

Cadet
Joined
May 2, 2013
Messages
7
Re: 1978 70 hp johnson

Thanks for the info. Everyone here has been very helpful. I really appreciate that.
 
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