1976 75HP Evinrude - Question Boat Service Companies Evaluation

[StickyWidget]

I have a 1976 75HP Evinrude, I have rebuilt all 3 carbs and replaced spark plugs. I checked compression and spark on all cylinders.

Service place is saying I have no spark on second cylinder.

The boat runs high idling, and will die if you slowly accelerate the throttle under load.

If I tap the choke and gun the throttle it will run WOT all day long. Every time I want to get back to WOT I would have to tap the choke in at the same time.

After rebuilding, all I've done, nothing seemed to change it's operation. I bought a timing light and it was reaching the appropriate max RPM (5600 I believe).

When I spark tested it last year, it looked OK to me. 7/16th Gap it jumped I believe.

This motor has run the same since I've owned it for about a year now. I took it out on the river the same day I put it in the shop, it still was running the same.

They say it needs a new power pack to the tune of about $150 for the part alone. $300 something to do it.

My questions:
Can a powerpack be "bad" and still jump a 7/16th gap?

Does my engines running the way it is look like it could be the powerpack?

Can a powerpack intermittently work? I haven't noticed surges in power at all.

How hard is installing a powerpack?

In a 15ft tri-hull fiberglass boat, would a bad powerpack still allow the boat to hit 30MPH? I have had this boat at that speed and pulling tubes all summer, seems like it couldn't do that on two cylinders but what do I know.

I don't intend on paying their prices if at all possible just was hoping for a "you tell me whats wrong and I'll fix it" approach.

Any help you can offer would be appreciated.

 

[eavega]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

To answer your questions to the best of my humble abilities:

Can a powerpack be "bad" and still jump a 7/16th gap?

I don't believe you will get proper spark on all three cylinders if the powerpack was bad

Does my engines running the way it is look like it could be the powerpack?

There are very specific tests to check all your ignition components. You will need a multimeter with a DVA attachment to read peak voltage. There is a link somewhere on iBoats for a company that sells the attachment for like $35 shipped, either that or some smarter iBoaters have posted instructions on building one yourself

Can a powerpack intermittently work? I haven't noticed surges in power at all.

My understanding is, no, not for any length of time. I had a power pack go faulty on me one time and it was like someone had pulled the killswitch. Motor went from sparking just fine to no spark on all 3 cylinders.

How hard is installing a powerpack?

As long as you have a wiring diagram or note what wire is connected to which terminal, you are looking at three bolts, plus the screws for the cover and the screws for reattaching all the wires. Nothing complicated about installing a power pack.

In a 15ft tri-hull fiberglass boat, would a bad powerpack still allow the boat to hit 30MPH?

Probably not. I had a 15' Tri Hull with a 70 HP Johnson, and I would get about 32 MPH as a top speed @ 5400 RPM. Dropping a cylinder probably would knock that down to about 3000 RPM.

don't intend on paying their prices if at all possible just was hoping for a "you tell me whats wrong and I'll fix it" approach

I'm going to venture a guess that you are suffering from the "Midrange Flat Spot" problem that was encountered with the 1976 70 and 75 HP 3 Cylinder motors. Only reason I knew about it was because I had a 1976 70 HP that would do the same thing, and it was suggested to me to look up Johnson TSB 1144. According to the TSB, if you experience a hesitation in the mid-range that is resolved by blipping the choke to get through the midrange, then its probably leaning out through the midrange and you would benefit from the carburetor modifications included in the TSB. Word of warning, the modifications indicated are not for the faint of heart. It will require you to drill out some of the ports in the carburetors, so if you mess up you are S O L.

I have a copy of it stashed on one of my computers. Let me know if you want a copy, else tell your mechanic to take a look at the TSB that deals with the 1976 3 cylinder 70 and 75 HP motors.

Rgds

 

[StickyWidget]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

Is the TSB attached the one you were referring to?

 

[eavega]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

Is the TSB attached the one you were referring to?

The very one. Its amazing to think that a motor can survive for 30+ years without the modification recommended by the manufacturer, but I know my 70 HP was not modified. Easy way to tell, look for either the stamped "X" on the carburetor body, or see if the jet is .030 or .032. If its .032, then the carb has already been modified.

Good luck.

 

[StickyWidget]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

So the plot thickens, I brought the boat back home and promptly put my spark tester on the second clyinder, no spark.
Swapped the number 1 and 2 coils. Spark on both.
Switched them back and had spark on all three.
When I went to unscrew the power pack terminal cover I noticed the screws on the cover were finger tight only. I checked all the screws inside and tightened them all about a quarter of a turn.

I have never had a spark issue until taking it to the service place. They recommended replacing the powerpack. I was going to rule out a bad coil before biting the bullet on the powerpack price.

I have all the parts ordered for the SB 1429 modification. I am going to check a few more things before I go drilling in my carbs.

Its weird to me because this bulletin looks like the holy grail to my problems.

Will changing the Idle Orifice from the stock .030 to .032 likely make the engine idle at a lower RPM? If not what does changing that part do?

 

[eavega]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

Will changing the Idle Orifice from the stock .030 to .032 likely make the engine idle at a lower RPM? If not what does changing that part do?

Should not make the engine idle at lower RPM once the timing is set correctly. At least, it didn't change my idle RPMs a whit when I did it.

Rgds

 

[StickyWidget]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

I bought all the parts required by the service bulletin and with clenched teeth drilled bigger holes in the carb. Fired it up on muffs and sounded better than I have ever heard it run. Just got back from the trial run on the river, low and behold I now have throttle between idle and WOT. Thanks for the information!

 

[eavega]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

Great to hear! Hope you have a great season on the water.

Rgds

 

[classiccat]

Re: 1976 75HP Evinrude - Question Boat Service Companies Evaluation

great detective work guys!

and nice job on the Mod!!!