1975 Evinrude 70hp Lost Top End Power

[mav6759]

I have a 1975 70hp Eveinrude, I was out fishing and everything was going great. I went to start the motor came slowly out of some stumps and heard a thump like the prop hit one of the stumps. The motor shut down but started right up. I went to thottle up, but fhe motor had no power to put the boat on plane.
1. I checked for spark and I am gerting good spark to all three cylinders.
2. I just had the flywheel key changed, but have not checked it since this outting.
3. The carb's were cleaned at the begining of the summer (note: it was running good all that day)
Now I was told it could be the key again, or I am running off one or two cylinders. And I guess that is my question. If I am receiving spark from all the coils and all the plugs are firing, that should tell me that the coils and the power pack and good. Could cylinder still not fire even though the plug is firing.

 

[grsmnky1]

Re: 1975 Evinrude 70hp Lost Top End Power

Sounds like your prop is spun. When you heard the "thump" you did most likely hit a stump/log and the rubber hub of your prop, if it's a through hub prop, or the shear pin of a old non through hub prop, saved your drive/prop shaft from snapping or worse a crankshaft.

 

[mav6759]

Re: 1975 Evinrude 70hp Lost Top End Power

Thanks for the reply, I took the prop down and had it checked at an evinrude repair shop, they told me that the prop was good it was not sprung. The prop just slides on. I don't have a shear pin. I am hoping that as long as I have good spark the coils and power pack is good. I was testing the plugs one by one today, and I couldn't stop the motor from starting evening when I had one plug out at a time. I mean that motor jumped on without pumping bulb. I guess i have to check the flywheel key again, I just had it replaced last week. I don't know if this is true or not, but someone told me today that it I broke the flywheel pin again just enough for the motor to start and run, but not give it power. it that true

 

[Haffiman]

Re: 1975 Evinrude 70hp Lost Top End Power

If you have a timing light, hook it up and do a rough check.

 

[mav6759]

Re: 1975 Evinrude 70hp Lost Top End Power

I don't have a timing light, but the evinrude shop told me to take all the plugs out and spin the flywheel to bring the number one cylinder to top dead center. I was told if the pointer on the motor line up with the TDC on the flywheel the flywheel pin is good and the timing should be right. I don't think this is a timing issue, the motor starts right up with no problems even if I have plugs out. Im just not getting any power. I was told that the prop nut had to be torc'ed to 10 foot pounds, it was not. I was playing around with it with one finger. I'm taking the boat out this morning, I'll check to make sure its getting enough fuel to all the carb's, other then that I can't think of anything unless, I can still get a spark to the plugs with bad coils or power pack and the motor still runs. If anyone have any ideas, I could sure use them.

Mav

 

[eavega]

Re: 1975 Evinrude 70hp Lost Top End Power

.I was told that the prop nut had to be torc'ed to 10 foot pounds, it was not. I was playing around with it with one finger.
Mav

Unless the the castle nut has one of its teeth sheared off, the cotter pin should still hold the nut in place. Given that the prop shaft is splined, I don't think that is your issue...

Have you actually done a compression check on all three cylinders? If you are losing compression, then all the spark in the world won't drive the piston. That thump you felt may not have been you hitting a stump.

-E

 

[mav6759]

Re: 1975 Evinrude 70hp Lost Top End Power

Update, OK, I had the motor on the water today. It was doing the samething I took off the cow and find out while it was running that the choke was not on. I moved the choke to the on position and it ran great. The only problem now, I forget to put the carter pin back in the prop and while I was zomng around the lake, guess what, you guess it, the prop fell off. I really want to laugh and I did,,,,,dumb, dumb, dumb...now its off to ebay to find a another prop.

Mav