1973 Evinrude 9.5 Power issue at WideOpenThrottle

[skyzend]

Just replaced MagnetoCoils, Condensor and Points.
carb has been recently rebuilt and good clean plugs have been installed.
Just finished a 25km run to test things out. Prior to the electrical work being done, this power issue did exist, and all electrical was the factory installed equipment (37 years old).

Boat is a 12 foot aluminum.
I get normal acceleration for about 3/4 throttle and then no more power or RPM during the final 1/4 throttle.

With just me in the boat things are stern heavy so the boat is not trimmed.
The motor seems to be fighting for RPMs but cannot enough horsepower to trim the boat and get the nose down. I'm just plowing through the water and RPMs are low. Note: Motor is mounted with shaft angled forward to force a trim with nose down.

If while at full wide open throttle I lean enough forward the nose comes down a bit and the RPMs start to build. Things progress until the boat is trimmed and the RPMs build to normal Wide Open Throttle speed and the boat is now clipping along at what is normal full speed. Now that I am there the motor can maintain this and can sit normally until I slow again on purpose.

The question is why won't the engine punch through the final RPM barrier to get the boat trimmed. Seems like there are not enough horses. Could this be a timing issue. I set the points exactly on .020 inches per spec. It could be that the .020 is a little tight and the actual gap could be a fraction under say .018-.019 hard to say really. If so this would retard the timing a bit I think. Could this be the cause? I had similar issues before I started and the points were set a little wide (factory setting).

Could this cause the symptoms I mentioned.
the only other thing I can think of is maybe the fuel pump is having a hard time keeping up at the higher RPM, but I'm not totally buying into this as things run great once the RPMs are there.

Open to suggestions.

 

[ezeke]

Re: 1973 Evinrude 9.5 Power issue at WideOpenThrottle

The last page of section four of your factory service manual has the instructions on how to set new points to .022 or to reset existing points to .020.

Might be time for new rings.

 

[skyzend]

Re: 1973 Evinrude 9.5 Power issue at WideOpenThrottle

Ok, I understand the A/V Plate and the "parallel" when the boat is on plane and it is. We don't need to get into this discussion any more.

Before we get ahead of ourselves and start suggesting different props etc lets have a look at the issues I am having and what we know.

The prop is the original prop. This I know as the motor has been in the family since I was 15 years old when it was brand new. The same as the boat. This boat motor combination never had any problem getting to WideOpenThrottle and top speed. In fact the combination was never at any time considered an "underpowered" combination .... quite the opposite.
Both Boat and motor have been parked in various degrees of storage for about 30 years and never run.

The motor was not heavily used when we were using it. Probably a dozen or so times a year over about a 4 year period until about 1977.

I have since revived the motor, checked the water pump impeller rebuilt the carb and redone the electrical. Changed crankcase oil etc. I have also performed compression tests and all is within normal operating spec. With the cover off it looks new.

Now lets look at the main issue. At 3/4 throttle the engine is working hard pushing the boat (not on a trimmed plane yet). Additional throttle is not providing RPM. The forces on the prop are significant enough to not allow any RPM to build up. This should NOT be the case. Additional throttle on this setup should be enough to punch the prop to higher RPM and eventually trim the boat. The prop pitch is not the issue here. With the factory installed prop, this motor should have the HP to run the motor near max RPM regardless of the speed of the boat.

From what I can see from the throttle and carb linkage, at about 3/4 throttle the carb is already wide open. The remaining 1/4 throttle just advances the timing without opening the throttle as it is already open full. This leads me to believe this is a timing vs Horsepower curve thing.

I think I will recheck the throttle linkage adjustment to make sure it is set properly. I am still curious as to what a very slightly smaller gap than .020 on the points would cause (1 or 2 one thousands smaller). Maybe its better to error 1-2 one thousands over than under).

Actually I will also pull the flywheel and give the points another check to see if there was any settling of the points now that the engine has been run a bit.
Remember that changing the point gap one way or the other will cause advanced or retarded timing.

Finally, Lets remember that the boat can reach both speed and RPM, but to do this a slight change in the Boat plane, prop resistance is needed. I'm also thinking that this might have something to do with the carb float not being set 100% accurately, excessive boat angle may be putting stress on the float restricting gas into the reservoir to the point that the engine is starved (No Horses or RPM). A slight change in boat angle causes the whole starvation situation to adjust away from a critical point.

Lots of thinking out loud ... and a few things to double check.