1986 Johnson 150 GT

firejunky

Seaman Apprentice
Joined
Sep 30, 2009
Messages
38
Let me start by saying that I am new to the site, and boat ownership. I don't know very much about out boards. I just purchased a 85 Ranger with a 86 Johnson 150. When i went to look at the boat the owner put the muffs on and fired it up. The motor started, but was doing this irregular sorta surging thing. He pumped the bulb and it cleared it up for a short while, then it started doing it again, I also checked the comp. on all cylinders (95-100). I bought the boat anyway.

It was a week before i could put the boat in the water and try it out. When i put the boat in at the marina it started but was doing that surge thing. I idled to the outside of the no wake zone and gave it some throttle. The motor just kinda fell on its face and would not pick up any speed. I made several attempts. One time the boa almost came up on plane but the bogged down. The motor also died several times during the test trials. Finally i said screw it I will take it to a mechanic when i get home.
In the mean time i decided since i'm on the water and it's a nice day i think i will just fish for a little while before i put her back on the trailer. After fishing for about an hour i fired her up again. The motor seemed to running smoother, so I idled out to the no wake zone and pushed on the throttle. She took off WOT 65 mph. I ran her for about 20 min. and put her on the trailer.

Two days later: I put her back in at the same place. started her up, running ruff again. went to give throttle nothing, just as before, tried for several minutes to get going, finally she takes off. I ran her for awhile then fished awhile, changed locations several times and she ran fine. I was heading back to the ramp, idling through no wake zone, and she started running ruff again.

I am thinking carbs, but really have no clue. any suggestions?
 

jonesg

Admiral
Joined
Feb 22, 2008
Messages
7,174
Re: 1986 Johnson 150 GT

Its new to you and you have no history with it .
So it would be wise to go all through it from top to bottom.
Get the factory manual.
www.outboardbooks.com

Compression is good.

Get a spark gap tester from the auto store and set it to almost 1/2 inch gap.
It should produce a bright blue spark ( all sparkplugs out).

Fuel pump sounds like its shot as pumping the bulb pretty much proved that.

Drain lower gear oil and check for milky creamy oil , if its clear honey then refill with new oil and replace seals on drain screws.

Remove prop, check for monofilament on the shaft, grease shaft and reinstall prop.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1986 Johnson 150 GT

It's either fuel or spark related. Check the spark when the engine is under load and it starts to run poorly. An inductive timing light will tell you if each plug wire is firing correctly or if it is misfiring. If the surging is corrected by constantly priming the fuel hose bulb the pump may be weak. Carbs can leak fuel when the engine is tilted up. The excess fuel runs down the inside of the airbox and gets recirculated through #6 cylinder-it can run rough till that fuel gets burned off-usually a only a minute or so.
 
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