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1985 70 Johnson getting on plain problems

L

Lazeronu

Contributing Member
Hi all! Thanks in advance for all the suggestions.

Just replaced a blown 82 75hp evinrude with an 85 70hp Johnson.

Took the boat out with 1 passenger and all ran fine first get up. Was able to run at 5k rpms and about 30mph. Exactly what if should be doing (on a 01 bass tracker pro team 175). Problems started when I came down from full throttle. When dropping to neutral motor would rev to 3k rpm. So I adjusted the throttle cable a couple turns and was able to get the rpms down to 1k at idle and when coming off full throttle. Only problem with this is that now I had to nurse the throttle up for it to kick into full throttle and take off or it would bog out and die.

Soo--- took the boat home and did a lync and sync. Made sure timer base was moving freely (it does seem like it could move a little more freely but I didn't want to mess with that just yet) carbs were horizontal at WOT, and made sure cam was just touching the carb adjustment rubber. All was good where the throttle would carbs would start to open just slightly after the timer base moved forward.

Took the boat out with 3 people, and ice chest, and fishing gear. Boat idled great at 1k RPM, but when I went WOT I could not get it to get on plain. I would max out at 3k RPM. The only way to get it in plain was 2 things (I should have tried just one but didn't like an idiot). 1) pump the primer ball which would get hard to start , then while pumping continuously would stick collapsed while it was squeezed and feel like it was sucking air from ball back to the fuel tank 2) have my buddy move to the very front of the boat. At the point, the boat still struggle but we got on plain at 4.7k RPM and 25mph.

Compression is 125, 125, 115. Good spark on all 3 cylinders. I will post a video of the timer base moving, and you tell me if that is sticking too much or not.

So a few questions:

1) running WoT at 3k RPM is bad right???
2) can this be fuel line related
3) am I overpropped for 3 people and the extra weight?
4) all else is welcome!!
 
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You are over propped a 3 blade 17" pitch was pretty standard for those motors to go to a 4 blade you usually drop 1" in pitch. You should be idling about 700 rpm in gear and max rpm should be 5500 rpm. There is a mark on the cam where the carbs should start moving for the link and sync.
 
flyingscott said:
You are over propped a 3 blade 17" pitch was pretty standard for those motors to go to a 4 blade you usually drop 1" in pitch. You should be idling about 700 rpm in gear and max rpm should be 5500 rpm. There is a mark on the cam where the carbs should start moving for the link and sync.
Click to expand...

The cam mark is lined up and the carb butterflies are closed. How would I adjust the idle?
 
The idle needs to be set on the lake when it is warm and in gear. Assuming the link and sync is correct, to adjust the idle look at the 2 silver screws on the side of the motor on the throttle linkage. The upper screw is the WOt stop the lower one is the idle screw you will also need to adjust the throttle cable to make sure it goes snug to the stop. There should be a gap between the carb roller and the cam you do not want those tight together. While setting the idle speed you do not want the cam touching the carb roller, The idle speed is set using the timing not the carbs. After the idle is set you may need to re-do the link and sync.
 
Ok great! I just purchased a different prop and will throw that in there. I will then take it to the lake to set the idle in the water. I appreciate the responses!
 
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