150hp johnson dies at full throttle and on lower rpm

[quarterhorse99]

have a 1986 150 hp johnson that takes a little while to start. It will start if u choke it and rev it up to the highest. When u bring it down it wants to die. Once i am able to get it in gear 95% of the time it dies under any load. Then out of no where it will take off and run like a champ topping out at 55. The other day it died in full throttle. Very inconsitent running. Never no when it will run. One minute it will the next it wont.

 

[greenrage4]

Re: 150hp johnson dies at full throttle and on lower rpm

Areyou sure you don't have my boat? Have you figured out the problem yet. Mine does the same thing. I replaced the oil reservoir and lift pump, I also changed the spark plugs. I ran great for the day but by the end it still did the same thing

 

[MikeB0307]

Re: 150hp johnson dies at full throttle and on lower rpm

Sounds like carburation/fuel issue. I'd check filters and for restriction in fuel delivery or vent. My '89 GT150 acted similar and mine was a combination of a slight restriction at the tank anti-siphon valve and the carb linkage sinc. My best diagnostic tool is the factory service manual, it has step by step symtom and diagnostic charts.

 

[emdsapmgr]

Re: 150hp johnson dies at full throttle and on lower rpm

You may be losing spark to one or more cyls. Weak ignition components tend to fail once they heat up to normal operating temps. When the engine craps out the next time you are on the lake-put an inductive timing light on each plugwire and crank the engine. The flashes from the gun will show weak firing, no sparks, and intermittent spark. That engine has dual identical power packs, one controls the spark to one head. They can be swapped for testing purposes.