1977 Johnson 75 HP stinger-Won't accelerate

[John Kat]

I have a 1977 75 hp Johnson that I purchased last Feb. The model # 75e1r77s serial #j4750914. I have put new plugs, de fogged the carbs, changed water pump,and fuel pump and filter. New tank and hose and bulb. The last two times I've taken the boat out,it starts fine,idles great but after running for some time at fast throttle(4000rpm +) it will bog down and won't accelerate past 2000rpm. It will troll or idle and start fine but feels like one or two cylinders is cutting out. Something electrical or carburation??

 

[Bass Runner]

Re: 1977 Johnson 75 HP stinger-Won't accelerate

Welcome to the forum, sounds like the power pack is heating up and loosing it, you can test by taking hair dryer and let it idle and heat up the power pack if that's not it, it may be a float in one of the carbs hanging open a little and flooding it down, when it went down did the motor run rough or just slow down? if it was rough i might be a coil, check them for cracks or burnt spots.

 

[John Kat]

Re: 1977 Johnson 75 HP stinger-Won't accelerate

The motor would run a little rough but its hard to tell at that low rpm. I ran it all day and it wouldn't go more that 10mph.

 

[inohv8]

Re: 1977 Johnson 75 HP stinger-Won't accelerate

my 65 horse does the same thing.. the power pack is good.. tried with new one.. had problem with one cyl.. blow-by.. waiting for pistons to rebuild.. also.. there is a temp switch on some engines called s.l.o.w. for the acronym..forget what it stands for.. but will not let the engine rev up and overheat itself... that sensor could be bad.. this is not the temp sensor.. it is an overtemp sensor..<br />Inohv8

 

[Walker]

Re: 1977 Johnson 75 HP stinger-Won't accelerate

That motor doesn't have S.L.O.W.<br />Do a compression test and get back here with the results.