'78 evinrude 70hp won't plane

This is my first post. However, I've read through many older posts concerning this problem. I'm including as much information as I can. I've also followed the advice already given here as best I can. <br /><br />Cleaned the carbs (replaced one gasket). <br />Checked the plugs (their in good shape and gapped right). <br />Made sure the plugs are getting fire (wires fit snug). <br />Checked the fuel lines (they are not blocked and on secure, no leaks). <br />Used new (and proper mixed) gas.<br />Checked the bulb while operating the engine (it stayed hard).<br />Checked the carb levers (connected to the control cables) to make sure they would open completely.<br />Checked compression (readings showed they were all at/near 100). <br /><br />I thought the compression was a little low, so I opened it up and found slight scaring in cylinder #2. #1 and #3 had less scaring, but it was present. <br /><br />I checked the pistons by pushing down on them right after they starting going down. #2 would give with a little "pop" sound. I think the rist pin is that problem.<br /><br />I'm lead to believe it needs to be bored.<br /><br />However, some wise men here have suggested replacing the power pack to other people with the same problem.<br /><br />More info: It has always run fine. Purchased three years ago. The problem started five weeks ago. <br />It began by not planing when I gave it full throttle. So I pulled off the gas for a while a then would get back on it. It will occassionally bog and die when I do this (acts like it's flooding). Most the time (when it's wide open) it just cruise's along like it's waiting for more gas to get the rpm's up. <br />I take it out once a week. On the last three trips it never planed. The two trips before that the problem was sparatic.<br /><br />My understanding about a bad power pack is it gets too hot. Then it doesn't operate correctly. So the boat will plane for a while (the pack isn't too hat), and then stop planing (once the pack gets too hot).<br /><br />Should I try a new power pack first? It's a lot cheaper than boring the cylinders and replacing pistons.

Re: '78 evinrude 70hp won't plane

That would also be guessing and possibly spending money that you do not have to.<br /><br />That is what we are trying to avoid here.<br /><br />How close to 100 were the compression readings.<br /><br />Are you sure there is spark to all the cyls?<br />Do a drop test.<br /><br />While the engine is running pull off spark plug boots and see if there is a change in the way it runs. The one that does not cause a change will be the one that is the problem.<br /><br />Did you clean the carbs or rebuild them?<br /><br />Scoring usually indicates broken rings. Is the scoring on the exhaust side or the intake? Or is it everywhere?<br /><br />TMD

Re: '78 evinrude 70hp won't plane

I rebuilt the carbs.<br /><br />The drop test (on all three plugs) produced a change everytime.<br /><br />Compression gave 105 for #1, 100 for #2, 100 for #3.<br /><br />#2 has scoring everwhere. #1 And #3 has scoring only along the exhaust ports.

Re: '78 evinrude 70hp won't plane

Those compression readings are readings of an engine that is ready to be rebuilt.<br /><br /> <br /><br />TMD

Re: '78 evinrude 70hp won't plane

I'm beginning to think that more and more. <br /><br />Thanks Doc for the assurance I'm heading in the right direction.