70hp johnson wont rev up

[stinkbait85]

My brother inlaw just bought a tach to put on his boat when he bought the motor several weeks ago and the tach reads 2500 and hits a rev limiter. The motor goes bah bah bah bah lol. Anyways I'm not sure if johnson tachs are universal to all johnson motors or to specific motors. 3cylinder v4 v6. The rev limiter is set to 6000 but never gets past 2500 before it hits the limiter. What's up?

 

[bowman316]

Re: 70hp johnson wont rev up

what year motor?
there is a screw near my throtle body, that you can screw in to limit how far you can open the throttle. Maybe that screw is screwed too far in towards the throttle arm?
but is sounds like something to do with a computer, if this is a newer motor. maybe the tach is set wrong, as far a sthe poles go. try unhooking the tach.

 

[stinkbait85]

Re: 70hp johnson wont rev up

Let me say this he took the boat out yesterday for the first time with the 70 on it and he says it was hitting the rev limiter before it reached its potential top speed. I think it may have the wrong pitch prop on it and the tach is just reading wrong. Its on a 17ft polar skiff. Not sure of the weight ofd the boat but I believe its a 17 or 19 pitch prop on it. Any advice is appreciated

 

[stinkbait85]

Re: 70hp johnson wont rev up

Took the tach loose and still bumps like hitting a limiter. Could a carb issue cause this?

 

[Faztbullet]

Re: 70hp johnson wont rev up

Depending on year, some engines had a S.L.O.W feature that reduced the rpm to 2500 if hot. If engine is not overheating and has this feature disconnect the orange wire from sensor on head to pack and retry. If it works ok it a bad/shorted sensor.

 

[bowman316]

Re: 70hp johnson wont rev up

does the motor sound like it is at 3/4 throttle, or 1/2 throttle. big difference there. 17 mph sounds like 3/4 throttle to me. i have a 70 hp evinrude, and it goes 25 mph max.
if it was a prop issue, it would not sound like a rev limiter, it wouild sound like your trying to go up a big hill in 4th gear instead of 3rd gear. you know that sound that tells you it is time to down shift in a manual transmission truck? that is what tells you you are over propped.

with the moror off, put it to full throttle, and see if the carbs open all the way, and if the throttle arm advances as far as it can.

 

[stinkbait85]

Re: 70hp johnson wont rev up

Ok wentout and messed with the motor here in the yard with the muffs on it. At 2500 it is bah bah bah bah bah like a rev limiter. So I know its not the prop now. Ima try the orange wire thing and clean the carbs. Then ima see what's up

 

[bowman316]

Re: 70hp johnson wont rev up

is this an old motor? what year?

 

[stinkbait85]

Re: 70hp johnson wont rev up

Ok I unplugged the sensor and she revs up now thanks a million

 

[stinkbait85]

Re: 70hp johnson wont rev up

well now i have 2 more questions. how do you take the sensor out of the head? i unscrewed the nut but the rest stayed in the hole. does the head need to be removed to get it out? also how do i know it's not something in the cdi box causing the problem and cleared up when the sensor was unplugged?

 

[bowman316]

Re: 70hp johnson wont rev up

so you never took the head off? If she rev's up now, i would not bother with it. But you would have to take the head off the get that device out of it.
Just make sure that your engine is not actually overheating. Make sure it is pumping water. And test you overheating alarm.
with mine, there is a small slot on the control box, above the key. turn on the ignition, and touch a piece of metal the that piece of metal in the slot. and you shoudl hear a loud alarm/beeping sound. that means your overheating alarm is working.

 

[stinkbait85]

Re: 70hp johnson wont rev up

Well I got it out of the head without taking the head off. I just looked up the part online to see what it looks like and dug it out with a small flathead screwdriver. And I can't see how the motor could be overheating when I first fire it up. Water stream is good. Reckon ill try the temp switch

 

[Faztbullet]

Re: 70hp johnson wont rev up

When its out you can test sensor with a meter and hot water. It unlikely its the pack....