1974 70hp Evinrude won't rev above 3k.

[sycostang67]

Last week we were out on the lake and at some point I noticed I had pushed the throttle all the way forward but the motor was only turning about 3k rpm. The motor is a 1974, 70hp Evinrude. The tag on the motor says it makes peak power at 5k rpm. While I doubt I will need to go that fast, I don't like thinking something is wrong. On my throttle control stick, the first 1/3 of travel seems to be dead space. I watched the linkage on the motor and it doesn't begin to move until the stick is that far forward. It will go into gear right away as soon as I move out of neutral but as I said has that no throttle dead spot. The boat is a 1990 Sunbird, original controls as far as I can tell. I took a peek at it but didn't see any way to adjust anything from the outside. If I open up the box am I likely to find a way to remove the dead space?

 

[flyingscott]

Dead spot in the throttle is normal and built into its operation. You cannot have the motor accelerating while you are shifting otherwise things will break. First thing to do is a spark and compression test it sounds like you may be running on 2 cylinders. Second thing to do is make sure the carbs are opening all the way.

 

[sycostang67]

I have the tools to pull that off, will probably be later this week but I'll get those things checked.

 

[sycostang67]

Test results are in. I have spark on all 3 cylinders, verified with light and pulling wires with motor running. Compression check, #1-145psi, #2-130psi, #3-130psi. The cable is moving linkage to open the carb as far as it can go. I was able to adjust the stop screw and get 200 more revs so it tops at 3200 now.

 

[racerone]

What stop screw did you adjust ?------Hopefully you left maximum timing advance right were it was.-----Make no adjustment using the ---" I wonder if this will help approach "------Perhaps check the flywheel key ?----Make sure carburetors are clean before taking boat out again !!

 

[flyingscott]

What do you mean the cable opens the linkage as far as it can go. Are the butterflies in the carb opening to 90 deg or not.

 

[sycostang67]

The circled screw is the one I adjusted, I backed it out about 1 turn. I disconnected the cable from the linkage and checked how far the linkage moved on its own. I couldn't see far enough through the fogging holes to see the butterflies. I will have to pull the cover off tomorrow.

 

[sycostang67]

I just got the cover pulled and verified the throttle blades are opening all the way.

 

[sycostang67]

What stop screw did you adjust ?------Hopefully you left maximum timing advance right were it was.-----Make no adjustment using the ---" I wonder if this will help approach "------Perhaps check the flywheel key ?----Make sure carburetors are clean before taking boat out again !!

How do I check the flywheel key? Can I see it by removing the large nut on top?

 

[Bosunsmate]

How do I check the flywheel key? Can I see it by removing the large nut on top?

Put the #1 cylinder to TDC, your flywheel should then have 0Degs at the marker. Thats how i check without removing the nut etc and needing to retorque.
You need to read Post #5 and understand that totally
Also need to see the linkage in your picture that moves the timer base. Im unsure if that is properly working or not

 

[sycostang67]

Put the #1 cylinder to TDC, your flywheel should then have 0Degs at the marker. Thats how i check without removing the nut etc and needing to retorque.
You need to read Post #5 and understand that totally
Also need to see the linkage in your picture that moves the timer base. Im unsure if that is properly working or not

Ok, I will check the key and marker alignment. Where is the linkage that moves the timing and should it move when the engine speed increases? Also, what can I use to spray the carbs to help clean them? It seems regular carb cleaner could be harmful to a 2 stroke motor. This is my first 2 stroke, so I'm in virgin territory with some of this stuff.

 

[Bosunsmate]

The linkage to the timing comes off the main one that moves the carbs. Its almost obvious so if you cant see it then perhaps its fallen off. The throttle moves the timing first, this is how you get your initial engine speed increase, the carb opening comes in later. This is why you use a lot more fuel at high rpm. Engine increase at low rpm is due to timing advancement, most engine increase at high rpm is due to carb opening and thus dumping in much more fuel.
Carb cleaner is useless unless you put something like soft copper wire up every jet with it too ensure its clear. I do that then i blow wd40 or something up each jet, orifice and check it comes out somewhere else in full force, that way i know there is no blockage

 

[sycostang67]

I see it now, it seems to move pretty freely and then hits an adjustable bump stop. I did not play with any of that stuff.