1975 85 hp Evinrude looses power

[bimmerbit_93]

The model is 85593E. The fellow I bought this boat from said that the last time he had it out, it ran fine until they started back from across the lake. It would not run at full throttle. I took it out to see for myself and found that it ran fine even at full throttle for about 200 yds., then began to loose power like you were gradually pulling back on the throttle. After pulling back on the throttle, I found that it would run steady at 3200 to 3600 rpm. The motor is on a 1971 15 ft. Larsen. I checked the compression before I bought it and all cylinders are at 102-105 compression. The water seems to be circulating fine; I get spray from both holes out the back. I also checked the spark before starting it and all the cylinders fired consistently. It started immediately at the lake, and ran really well except for the high rpm issue. I also checked the fuel pressure from the fuel pump and it was 5.8 lbs. at the pump. I have read that this should be tested at the line that goes into the upper carb, and it tested it at the pump. Is this inaccurate? Thanks for any help or ideas.

 

[tashasdaddy]

Re: 1975 85 hp Evinrude looses power

check spark each cylinder, when it starts acting up, inductive timing light works for this. also could have clogging high speed jets. read Ethanol http://forums.iboats.com/showthread.php?t=299680

 

[bimmerbit_93]

Re: 1975 85 hp Evinrude looses power

Thanks for the ideas. I will try to get it out this afternoon and check the spark issue.

 

[iwombat]

Re: 1975 85 hp Evinrude looses power

Is it losing RPM or just thrust? Could be a spun hub.

 

[bimmerbit_93]

Re: 1975 85 hp Evinrude looses power

No, it actually loses power. I is like the throttle is gradually being cut back. Then of you run at lower rpm for awhile you can take it back up to full throttle, but it won't last as long as the first time. We shut it off for about 30 minutes, and when we started back up, it ran with no problem as long as you stayed below 3200 to 3600 rpm. If you try to open it up, it might reach WOT, but it will drop off again until you pull back on the throttle. I tried taking off the vacuum line from the fuel pump and there wasn't any fuel coming from the pump, a little spray from the line off of the motor. That is probably to be expected, isnt' it? I took the high speed jets out tonight and cleaned them. The one on the lower left is the only one that looked dirty (yellow film on the inside of the cap and a little on the jet). I'm going try and get in on the lake tomorrow to see if it makes a difference. I'll try the spark tester at full throttle and see what I get there, also. I'm beginning to think I need to rebuild the carbs and replace the floats. ????

 

[crb478]

Re: 1975 85 hp Evinrude looses power

Make sure your tank is vented properly, if you have a different tank fill it with fresh gas and see if the problem is still there. Also have you tried pumping the bulb when this is happening? Lastly with the air silencer and cowl off try to spray some premix directly into the carbs and see if they pick up. That will help you narrow it down between fuel or electrical problems.

 

[bimmerbit_93]

Re: 1975 85 hp Evinrude looses power

I did use a different tank last time out; the old fuel is a year old so I haven't used it. I haven't tried spraying gas in the carbs or using my spark tester under load. Thanks for the ideas. I certainly helps narrowing things down.