Intermittent half power mode '77 70hp Evinrude

[sealarks]

I am wrestling with an intermittent issue with my 1977 70 hp Evinrude (70773). The issue is most prevalent after the engine is run full speed on the water and heats up...and is then started and stopped at slow speeds moving from one fishing location to another. When attempting to then return to full speed, the motor only delivers half power when the throttle is wide open. It will run rough and stay in this mode for a bit and then normally the issue will clear with a drastic return to full power mode. The change is so drastic I thought linkage was sticking and kicking free but this doesn't seem to be the case. The issue has occurred going from full speed to half power, but only rarely.

Based on all of the good advice I have read from the responses that have been offered to others with similar issues on this forum, I have replaced the coils, plugs and wires, power pack, and rectifier. Have also replaced the fuel pump and have sprayed the carbs with carb cleaner

Upon returning to dock in this mode last time, I pulled the plugs to find that they were all wet with gas with the middle plug being noticeably wetter with bubbles around the spark plug electrode.

Would appreciate any advice on the next place you would look to tune or replace parts to clear the issue. The motor hasn't been heavily used over the years and runs like a champ except for this intermittent issue.

Thank you for any assistance.

 

[basketweaver]

Re: Intermittent half power mode '77 70hp Evinrude

When you find out the problem let me know. I have posted the same problem with my 77 70hp Evinrude but have been unable to get any response

 

[billy4hp]

Re: Intermittent half power mode '77 70hp Evinrude

I am wrestling with an intermittent issue with my 1977 70 hp Evinrude (70773). The issue is most prevalent after the engine is run full speed on the water and heats up...and is then started and stopped at slow speeds moving from one fishing location to another. When attempting to then return to full speed, the motor only delivers half power when the throttle is wide open. It will run rough and stay in this mode for a bit and then normally the issue will clear with a drastic return to full power mode. The change is so drastic I thought linkage was sticking and kicking free but this doesn't seem to be the case. The issue has occurred going from full speed to half power, but only rarely.

Based on all of the good advice I have read from the responses that have been offered to others with similar issues on this forum, I have replaced the coils, plugs and wires, power pack, and rectifier. Have also replaced the fuel pump and have sprayed the carbs with carb cleaner

Upon returning to dock in this mode last time, I pulled the plugs to find that they were all wet with gas with the middle plug being noticeably wetter with bubbles around the spark plug electrode.

Would appreciate any advice on the next place you would look to tune or replace parts to clear the issue. The motor hasn't been heavily used over the years and runs like a champ except for this intermittent issue.

Thank you for any assistance.

Sounds like you may have some junk floating around in the carbs.... I would order up three rebuild kits w/ needle and seat assemblies and tear them down. Also it would be a good idea to replace all the fuel lines at that time if it has not been done recently as todays fuel with ethanol is not compatible with older rubber lines and is causing quite the issue in the marine world....

Good luck...

 

[sealarks]

Re: Intermittent half power mode '77 70hp Evinrude

Thanks so much for the advice.
I've found a place where I can buy the carb rebuild kits.
The only question I have is whether I should take on a carb rebuild job or if I should take it in to the shop. I have a picture in my mind of opening the carbs, springs flying everywhere and never getting the motor to run again. Are my concerns well founded? Or, is a carb rebuild within the reach of an amateur mechanic that has made the changes I have undertaken so far? Are there any other surface level changes that might clear the issue?

Also, I'd appreciate any detail that you or others can pass on in reference to the replacement of hoses in old boat motors. Should the lines between the gas tank and motor be changed, the input lines to carbs, or both be changed? I saw the pictures of the results that can happen with ethanol and old lines, but there was no comprehensive guide in reference to what should be changed and how you can tell if your existing line are achohol/Ethanol resistant.

Thanks once again for all of the help and appreciate any insights.

 

[billy4hp]

Re: Intermittent half power mode '77 70hp Evinrude

Thanks so much for the advice.
I've found a place where I can buy the carb rebuild kits.
The only question I have is whether I should take on a carb rebuild job or if I should take it in to the shop. I have a picture in my mind of opening the carbs, springs flying everywhere and never getting the motor to run again. Are my concerns well founded? Or, is a carb rebuild within the reach of an amateur mechanic that has made the changes I have undertaken so far? Are there any other surface level changes that might clear the issue?

Also, I'd appreciate any detail that you or others can pass on in reference to the replacement of hoses in old boat motors. Should the lines between the gas tank and motor be changed, the input lines to carbs, or both be changed? I saw the pictures of the results that can happen with ethanol and old lines, but there was no comprehensive guide in reference to what should be changed and how you can tell if your existing line are achohol/Ethanol resistant.

Thanks once again for all of the help and appreciate any insights.

Rebuilding a 2 stroke carb is really straight forward, nothing should come flying apart. I do recommend taking one carb apart at a time so you don't mix anything up between carbs. The jets should be fixed so you need to build a small cleaning brush, a stripped piece of speaker wire works well to push into the jets to get the crud out. An air compressor also really helps to blow through the various passages and jets. The most common mistake I see is not replacing the needle and seat assembly and incorrectly setting the float height. Other than that they are a snap to rebuild...

As far a replacing fuel lines, if you replace one, replace them all IMHO. Otherwise the one you don't replace will be the one that creates concerns down the road.

Good luck and take your time... It's not rocket science....

 

[Les Robb]

Re: Intermittent half power mode '77 70hp Evinrude

What I did to make it easier was to take all carbs off at the same time linkage intact. Got a box top for a case of standard copier paper and lined it with newspaper. Took linkage off and laid to right of carbs and then one by one removed bowls, seats, gaskets related floats etc and soaked in parts cleaner over night. After soaking take high pressure air ( if you don't have a compressor go to a real gas station ) and blow all the passageways out completely. If you have any dark amber to brown deposits left you need to soak for another day. With all the parts in line and linkage in correct position its a snap to reassemble. I would go with a full rebuild kit approx $30.00ea. And don't forget to replace all gasets and the fuel line hoses. That small tee in the center is NOL from Evinrude but you can find them in auto parts stores for vacuum system, that will work if you break yours taking hoses off.

Good luck and safe boating ya'll

 

[sealarks]

Re: Intermittent half power mode '77 70hp Evinrude

Although I appreciated all of the advice in reference to the carburetor rebuild, and I may still need to go down that path, I continued to have reservations about proceeding especially after draining the bowls and finding the gas ran clear. I continued to concentrate efforts on more potential surface level issues. One of the first things that I found originally was a cracked coil, so I replaced them all with the OEM parts. As it turns out, the plug wires were epoxied in to the original coils, however with the new coils the wires were separate. Given what I see as very poor engineering it was very difficult to connect the coil wires to to the coils making them prone to disconnect with engine vibration. The manufacturer also skimped on the wire using some sort of PVC that didn't connect well given the coil design.

I believe the secrets I learned were these, use high quality Hypalon plug wire that is thicker...less slippery...and more readily threaded to the post that you screw the wire into, make sure you use triple guard grease in the boot end that connects to the spark plug, make sure that you screw the wire on to the post of the coil rather than just trying to push it on.

Upgrading the wire and making sure to screw it on the post, seems to have fixed the issues I had. Took it out today finally, and it ran like a champ. If I had it all to do over again, I would have replaced the coils with ones I have seen from a different manufacturer that have a spark plug boot on both sides of the spark plug wire. I believe my original problem was a bad coil and all subsequent issues were associated with the intermittent connections of the coil wires caused by a poor design. A Google search on the coils will show the after market coil by a different manufacturer with spark plug boots on both sides that is a much better design.