1989 70hp evinrude topped out at 3300 rpm?

[bobbo268]

Just bought an 88 15' thundercraft with i believe an 89 70hp Evinrude outboard. When i give it full throttle, to the point where i can't push it down any further, the top rpm is 3200. What do i need to check? Could it just be the RPM gauge? before the speedometer stopped working it was max speed about 26mph, but i know boat speedometers aren't real accurate anyways. Thanks for any help

 

[jakedaawg]

Re: 1989 70hp evinrude topped out at 3300 rpm?

You most likely have the wrong prop. if everything else seems to be fine. You really should verify using a tach, not the one in the boat. Stevens products makes a great one.

 

[BonairII]

Re: 1989 70hp evinrude topped out at 3300 rpm?

Doubtful the prop is the culprit. The OP can't make up 2500+ RPM with a prop change.

I would verify that all cyls are firing and then make sure that your timing is advancing when you throttle up.

 

[phillnjack2]

Re: 1989 70hp evinrude topped out at 3300 rpm?

first of all make sure that full throttle on the remote is full throttle at engine end.
then look at prop size. etc

never trust ordinary boat tacho to be accurate, the settings on it could be wrong and be putting the clock way out.

Does it sound like its getting full throttle or does it sound like its bogging down etc.

unless your boat is extremely heavy then 26mph is very poor. but another 2500 rpms would mean speed is a bit high ????

as anyone near you got a gps to get accurate speed ?
just run along side another boat with gps will do !!!!!




phill

 

[boobie]

Re: 1989 70hp evinrude topped out at 3300 rpm?

First thing to do, is a compression check.

 

[bobbo268]

Re: 1989 70hp evinrude topped out at 3300 rpm?

compression was all equal when i bought it. I'm just going off the top of my head but i think it was around 120? thats just trying to remember, i'll have to check again. I'll also check the prop markings and i'll check that the full throttle on remote is full throttle on engine.

 

[bobbo268]

Re: 1989 70hp evinrude topped out at 3300 rpm?

Ok the throttle at the motor has about 3/4 inch to an inch of travel left. My neighbor said it is like that to adjust depending on the prop size so it doesn't over Rev. The prop is 17. There appears to be 2 places to adjust throttle travel. One is a spinner nut just after the throttle cable enters the motor and another one which is a large black apparatus that has an adjustable screw that stops the travel. So where do I go from here? Again its an 88 thundercraft bowrider 15ft and 89 evinrude 70hp

edit: oh, and forward idle/neutral is 500 to 600rpm per the guage
gps top speed at 3200 rpm (topped out at throttle lever) is 30mph
propeller: 13-1/4 x 17

 

[bobbo268]

Re: 1989 70hp evinrude topped out at 3300 rpm?

forgot to check the compression... :facepalm:

 

[bobbo268]

Re: 1989 70hp evinrude topped out at 3300 rpm?

anyone?

well just saw its a medallion tach and has 4 settings on the back. From another site:

1 - 4 cyl.
2 - 6 cyl.
3 - 8 cyl.
4 - 10 pole
5 - 12 pole

found on another site that it is:

1 - 4 cyl.
2 - 6 cyl.
3 - 8 cyl.
4 - 12 pole
5 - 20 pole


From what i've read 3cyl is 12 poles. My tach only has 4 settings, not 5, and it was on 1, but its jammed and won't go past 2. I am going to try and take it apart to see if i can loosen the selector and hope 4 is 12 pole, since its the furthest it goes and there is no 5. Can i change props to help speed or is 30mph (gps reading) good?

 

[phillnjack2]

Re: 1989 70hp evinrude topped out at 3300 rpm?

"My neighbor said it is like that to adjust depending on the prop size so it doesn't over Rev."

Your neighbour dont know anything about boats by the sound of it.
if its running a 17inch pitch on 15ft youl probably not over rev it.

as for 30mph at just 3200 revs ????? speed seems very high for just 3200rpm

you need to get the throttle lever fully forward and look into the front of the carbs and see if the flap is fully open.
If not then adjust the cable untill it is.
You should have full throttle no matter what your friend says.
the engine is meant to run around 5000 to 55000 so if its half inch of play then your rev counter cant be too far out.

Get someone with a proper tacho gun to check the revs for you.




phill