1986 70HP Johnson has no power at WOT

[cmchesse]

This is my first time posting, I bought my boat a week ago and have been reading this forum everyday since then. I have learned many things already and successfully launched and retrieved my boat 3 times. However, I am having a problem with power.

I have a 1986 70 HP Johnson outboard that seems to idle good, but when push the control into drive it dies. If you move quickly to WOT. it will run, but bogs down. does not accelerate at all. The engine had the wrong plugs when I bought it. We ran it for 30 minutes high speed. Then took it up a no wake canal for an hour or so. It accelerated to a plane coming out of the canal. When I slowed for some small boats, it would not produce enough power to plane again. At WOT it was like an idle. Can anyone help?

I am planning to spend the 4th on the river in our boat.

 

[kenmyfam]

Re: 1986 70HP Johnson has no power at WOT

Do a Compression check. Post photos of your plugs, check spark to each cylinder.
These are the basics to get started with your troubleshooting.
Report back your findings.

 

[kenmyfam]

Re: 1986 70HP Johnson has no power at WOT

By the way, welcome to iboats

 

[R.Johnson]

Re: 1986 70HP Johnson has no power at WOT

Check, and see if the timer base is going to full advance, and throttle plates are fully open. If so, do a compression, spark, and fuel check. A service manual would certainly help, In the long run, you will want one, unless you have on already.

 

[Nandy]

Re: 1986 70HP Johnson has no power at WOT

Hmmm, did you check your fuel lines? if you can idle for some time then it works it could be fuel starvation. Right now is hard to tell....

 

[cmchesse]

Re: 1986 70HP Johnson has no power at WOT

Wow, what a great response so far. I truly feel welcome already.

I just knocked off for the night. But I thought I would offer some additonal info. I do have a manual. But am a little intimidated by it.

This is what I have done:
The control box was very tight and difficult to use. In proper fashion for a newbie, I removed and opened it up only to see the tension bar. (I wondered what that knob was for) LOL...

I adjusted the throttle cable cam. On our maiden voyage, we noticed the carbs were not opening to full throttle. That has been corrected now.

Not knowing I checked the oil in the foot (Thinking binding)

I replaced the fuel lines and a new 6 gallon fuel tank with fresh oil/gas mixture at 50:1.

I replaced the spark plugs with he correct ones and set the gap to .40.

Checked the pee hole? for flow. Water is pumping great

We took the boat to the river again, same thing.

When home I pulled the plugs. The middle cylinder was wetter than the top and bottom.

On my last trip to the ramp, another boater was there. He said he was experienced at working on outboards and thought it may be a coil. He told me that the engine may sound ok at idle when it is out of the water, but with the load it could be dropping a cylinder.

I will check the compression and spark this week and report back.

Thanks for the help so far. I look forward to many more.

 

[cmchesse]

Re: 1986 70HP Johnson has no power at WOT

all 3 cylinders are getting spark. compression on all 3 cylinders is 115.
Pulled carbs, the bowels were full of gunk. Cleaning them now.

could still use any help you can offer.

 

[HighTrim]

Re: 1986 70HP Johnson has no power at WOT

It did sound to me like you had a fuel restriction, which you found out.

A couple tests that you could have done would be to spray pre mixed fuel into the carb throats. If it picks up a bit, there is a restriction there.

If pumping the fuel primer bulb picks it up, the fuel pump need rebuild/relaced.

Be sure to remove and thoroughally clean the jets/orifices. The servicve manual will cover this. Bare minimum get some machinist wire through them, then blow out with compressed air. This video may also help. You may need a special tool, or you could make your own out of a flat screwdriver as the pic by Frank describes below. Good luck to you.



http://www.meegsonline.com/tmd/TMDsVideoChronicle2.wmv

 

[wildmaninal]

Re: 1986 70HP Johnson has no power at WOT

Sounds like a carb problem to me. My motor was doing the same thing as yours at one point, I took the carbs off, cleaned, blowed them out (with 120 PSI coming from an air gun), rebuilt them, and did a link and sync.

I would also check for air/fuel leaks in the fuel lines. I replaced all my fuel lines, also rebuilt the fuel pump (when I first got the motor).

I believe you are on the right track, sounds like a fuel system problem.

 

[cmchesse]

Re: 1986 70HP Johnson has no power at WOT

May sound crazy but what is a lync and sync?

Does that have to do with tuning the 3 carbs?

Is the 115 compression good?

 

[mikesea]

Re: 1986 70HP Johnson has no power at WOT

comp is great,link ans sync is insuring the carbs open and close in unison,on 2 carbs you will see small set screws with the carb that has the throttle roller in the idle (no throttle advance,loosen the set screws on the other carbs,insure the throttle plate is closed,and then tighten set screws,there may be a link or definatly postings about a more through sink and link,a manual is best,some engines have a bit different set up

 

[cmchesse]

Re: 1986 70HP Johnson has no power at WOT

carbs are cleaned and back on the motor. Without any adjustment the engine runs smoother. That seems to be a good sign. Now to sync them up and get back in the water.

Shame it's raining like a monsoon.

 

[cmchesse]

Re: 1986 70HP Johnson has no power at WOT

We are in for a huge storm tonight. But I ran the boat to the ramp earlier and ran down the canal. It runs sweet now!

I can't wait for the weekend. I might even play hookie tomorrow.

Thanks to everyone for the help and support.

I'm sure I will have another question soon.