1977 70hp evinrude dead spot

[fireman57]

Re: 1977 70hp evinrude dead spot

bumping the choke just allows the mixture to richen for just a second and then it fixes itself for some reason until you back the throttle down again. Blocking off the intake to the carbs won't help because you are blocking the air for an extended period of time. The engine I am working on had a cylinder dropping after running WFO for about 20 seconds. I could squeeze the primer bulb and it would keep going so I thought was chasing a fuel problem until I got a buddy in the boat with the airbox off and it was getting plenty of fuel. I literally just changed out the power pack and coils (thanks again Jeff) so the loss of fire on a cylinder should be taken care of. These era engines are just mystery. I'm going to try to test it on the water today but don't know if I will get there or not. I'll let you know how this thing runs after I get it out.

 

[1kruzer1]

Re: 1977 70hp evinrude dead spot

Nope, no way 50 pounds compression is accurate. The engine probably wouldn't start, and if it did no way it would idle at all, and no way it would run with that much power. I couldn't really say how much slop between the throttle shaft and carb body is too much. Obviously the grease fix is a Band-Aid, and the only correct way to really repair this would be to replace the carburetor bodies, which to my knowledge are no longer available new. Aside from the above mentioned possibilities, my gut bet is that this is a carburation issue, either air leak or idle circuit restriction, or possibly low fuel level in one or more bowls. All you can do is attempt to address these and rule them out one at a time. It's exactly what I had to do on my motor, and as I mentioned before I about went nuts before I got the problem resolved. On mine the richer idle jets solved about 60% of the problem, and greasing the shafts took care of the other 40%. I've had no continuing problem with this symptom for the last four years. Not sure what else I can offer to help you on this one. I do sincerely wish you good luck, and hope you can get it resolved. These really are great motors, and there are literally tens of thousand of these still running out there.

 

[roonie]

Re: 1977 70hp evinrude dead spot

1kruzer1....should i bump up to .033 low idle jet first? I am already sitting at .032 which is the size of the part # you gave me for 77-78 years. Would it hurt to go up one more? I guess im just looking for something simple before i go at those carbs. lol

 

[fireman57]

Re: 1977 70hp evinrude dead spot

roonie my '78 gets plenty of fuel with the .032 and I have been through those carbs so much that my momma would be proud of the cleanliness. Just don't think the .033 will make a difference. It seems to not be able to make the transition from low speed jets to the high without some help.

 

[roonie]

Re: 1977 70hp evinrude dead spot

what about a hotter spark plug?

 

[ebauman]

Re: 1977 70hp evinrude dead spot

just so you know, there is more to fixing these carbs than just changing the low speed jet. You must also carefully hand drill out the 4 holes on the high speed nozzle with exact sized number drill # 55, then also hand drill out the 3 holes in the calibration pocket with exact sized number drills #56,57. The exact procedure is documented in OMC service bulletin # 1144. I have done this modification to my motor and now it doesn't miss a beat or stall !! Some one has actually posted the service bulletin on this forum just lately, do a search and i'm sure you will find it. Eric

 

[fireman57]

Re: 1977 70hp evinrude dead spot

Eric, sorry I didn't post this sooner. I found out that even though the engine wasn't overheating that the overheat sensor was shorting out the number one coil after you would run about 20-30 seconds at WFO. We unhooked it and it has run fine ever since. It is starting to act up again so I am going to look for that service bulletin that you found. If you can would you send it to me in a pm. i would appreciate it.