70hp Evinrude powerhead questioin

[UNCC Grad]

I've got a 1984 Evinrude 70hp with a tired powerhead. Compression, while even is only 95-100psi on all three cylinders after a good decarb. I have found a donor powerhead locally but it is a 1989 model powerhead. Will this work as a direct replacement?

 

[JB]

Re: 70hp Evinrude powerhead questioin

I would call 95-100psi and even a pretty good engine, Tar Heel. Those triples usually lose compression in the middle cylinder if there is a compression loss. That hasn't happened.

Differences in guages, technique and situation can make as much as 50psi difference in measured psi.

I understand this sense of urgency to do somethng to improve things, but I don't believe in fixing what aint broke.

How does the engine perform? Are there things you can do to the rigging to get better performance from the boat?

 

[UNCC Grad]

Re: 70hp Evinrude powerhead questioin

Possibly I'm not doing the compression test right. I know I forgot to open the throttle so that may have some effect. It's just been a constant battle to keep it running right. First it was sluggish out of the hole so I rebuilt the carbs. It is no longer sluggish out of the hole but now I can't get it to go over 3000+/- RPMs. I've checked spark and all three look good, even felt pretty good through the cheap pliers I was using LOL.

Along with the rebuilt powerhead, I've found a 1994 60hp Evinrude (VRO disconnected)that was rebuilt 2 seasons ago with power tilt and trim and controls. What I've been thinking about is getting the newer motor, keeping it for myself and selling the 1984 model in "as is" condition. I'm just tired of messing with the thing every other time I want to go out but I don't have the money for a brand new motor with warranty.

 

[borz170]

Re: 70hp Evinrude powerhead questioin

I really hope you decide to keep/fix this engine. My uncle and I have been working on an old johnson 70 hp for a few years. The engine runs well, despite the fact that it has sunk in salt water twice that I know of. This engine will plane out a 17' heavy old POS waterlogged cobia with 3 people, a dog and a cooler full of beer with strain, but it pulls it off. I have no idea what RPM's we are turning, but I would like to know. Keep the thing. It's simple, and it seems like you have some hands on abilities. You will probably be able to get this engine running at 5500 rpms with a few bucks and a bunch of good knowledge from the experts here.

Besides, My engine runs great and it sunk in salt water x 2. Has yours? Probably not...

 

[Dhadley]

Re: 70hp Evinrude powerhead questioin

Trying to install a 56 cid power head on a mid section for a 49 cid won't work. Unfortunately the newer powerheads will bolt up to your mid but the water inlet and exhaust passages are in different places.

 

[UNCC Grad]

Re: 70hp Evinrude powerhead questioin

Trying to install a 56 cid power head on a mid section for a 49 cid won't work. Unfortunately the newer powerheads will bolt up to your mid but the water inlet and exhaust passages are in different places.

Thanks for that bit of info Dhadley!

 

[Chinewalker]

Re: 70hp Evinrude powerhead questioin

That, and the driveshaft splines are different...
- Scott

 

[Dhadley]

Re: 70hp Evinrude powerhead questioin

Some of the 56 cid's did have 4-spline shafts. That's what's so confusing. Normally with OMC stuff, if a part bolted up it would or could be made to interchange. This is one of the rare cases that the part (powerhead) will bolt up but won't work.

 

[UNCC Grad]

Re: 70hp Evinrude powerhead questioin

I took my old motor out for a test run today. New plugs, fresh gas from a clean tank and no change. I did notice that it would run smoothly up to about 4K rpm and when given more throttle it would hesitate. If i pressed the choke in it would momentarily pick back up. Before I give up and buy the other motor I think I will disassemble and clean the carbs again using the relatively new gaskets and floats that are in them now. I refuse to drop more money into this motor at this point but my labor is free.

 

[Randybeall]

Re: 70hp Evinrude powerhead questioin

With reading what you have and what you have done, I would suggest that a careful Link&Sync is the next step after you reclean the carbs. Remember, Timing is Everything.