'76 Rude 75hp poor at altitude.

[jerrypark1]

I have a 1976 75hp Evinrude 3cyl that runs rough at best. Thanks to this great site, I've been able to troubleshoot to this point. I usually run at 5000-6000 ft. around Denver, but often up to 9000ft. I've had mechanics work on this several times with no improvments, so I'm taking it on myself. Compression good at 121-125 on all 3, good spark, rebuilt the carbs, good gas/oil, etc. Problem is when the motor finally gets up to speed, it will cut in and out like a lost cylinder. Further, it is very slow to get up to speed and usually needs a bit of 'feathering' to get it there. Occasionally, it will never get up to speed and I will need to limp around the lake to fish. Taking off the cover over the carbs usually makes it a somewhat better though. The plugs are almost always oily, so I'm thinking that re-jetting is needed. It starts and idles great, so I'm only guessing that I need to re-jet the high-speed (fixed). Currently running 61D jets, but I can't get any local help from the mechanic, nor is there an altitude chart listed in my Seloc manual. Advice?

 

[R.Johnson]

Re: '76 Rude 75hp poor at altitude.

At that altitude you need a #50D high speed jet.

 

[jerrypark1]

Re: '76 Rude 75hp poor at altitude.

Wow! From a 61 to 50...that's a huge difference in size. I got to admit, I'm a bit worried about running too lean and blowing the motor. (Maybe I've read too many posts in this forum and gotten gun-shy) With a difference that big, I'm suprised that the motor does run okay from time to time. Is the 50 that you stated for the 9000ft. range, or the 6000ft. Should I shoot for a happy medium at 7000ft? And if so, what is the recommended size? Thanks much for the help, it's appreciated.

 

[R.Johnson]

Re: '76 Rude 75hp poor at altitude.

3-6000 ft. #50D. 7-10000 ft. #44D, according to a notation in my 76 manual, a #55D was the stock jet for this engine, ift came with a #61 which was incorrect.

 

[jerrypark1]

Re: '76 Rude 75hp poor at altitude.

Thanks for the info R.Johnson. I've finally been able to track down some jets here in town. They only have 54D which isn't the recommended 50, but a heck of a lot closer than the current 61. I'll hopefull be able to install and test-run the motor this weekend if my fishing buddy, "The Drunken Goose" can get out of the house. Finally, to ease my paranoia, how do I know if the motor is running too lean? I saw 'blistered porcelain on plugs' in the manual and maybe a backfire, but is there anything else that would speak of a lean condition? Thanks again.

 

[jerrypark1]

Re: '76 Rude 75hp poor at altitude.

Just wanted to give an update.<br />I put the 54D jets in and tested this weekend....it has never run better. It hauls butt across the lake. BIG Thanks to R. Johnson for the info. Now I'm working on installing a tach to make sure I'm not over-reving.

 

[kntutt]

Re: '76 Rude 75hp poor at altitude.

Damn Fallen Rock you got yours running quickly. You run around Denver and if you go to 9000 feet I would guess we are looking at Dillon Resevoir. <br /><br />I am in Basalt and running up at Ruedi at 7800 feet and can't get this to run well at all.<br /><br />The people here have been very helpful, but changing the jets on my 1977 175 from 59C's to 54c's is giving me more of problem. <br /><br />Good luck with yours.

 

[jerrypark1]

Re: '76 Rude 75hp poor at altitude.

Sorry to hear you're still having problems, Kentt. I've been spending a lot of time on this motor and the jets were the final change. Complete fuel system rebuild, carb rebuild, powerpack, sync-n-link and finally the jets. It still needs some lower unit work, but that'll have to wait until the water gets iced-over. The previous owner apparently didn't believe in maintenance. Good Luck.