1971 Johnson 50ESL71S Carburetor Adjust Pointers

[jsrock563]

Rebuilt the carbs on my 1971 Johnson 50HP this weekend and need some pointers on how to go about adjusting them. Engine starts easy, runs great, but I think it may be burning a little rich. I'm getting a lot of smoke and black soot. The repair manual I have is rather generic for several generations of motors that span from 1971 to 1989 and I couldn't find any step-by-step tips. Can anyone help?

 

[Daviet]

Re: 1971 Johnson 50ESL71S Carburetor Adjust Pointers

Your engine uses fixed high speed orifices (jets), no adjustments.
The low speed needles are adjusted as follows, screw the needles all the way in until lightly seated and back them out 1 1/4 turn. Make final adjustments with the boat in the water and in gear. Adjust each carb until you get the best idle and then 1/8 further out.

 

[BonairII]

Re: 1971 Johnson 50ESL71S Carburetor Adjust Pointers

Are all cylinders firing? A dead cylinder will spit raw gas/oil right out the exhaust and be smoky.
If they are all firing, then adjust your "high speed needle"(assuming you have an adjustable needle). Turning the needle "in" will lean the mixture. Adjust at WOT while on the water not in a test barrel

From the limited knowledge I have...normally 1 1/2 turns out(from seated position) is a good starting point for the low speed needle. And 3/4 to 1turn out on the high speed needle. Those are just guesstimates tho.

 

[oldrudedude]

Re: 1971 Johnson 50ESL71S Carburetor Adjust Pointers

The factory manual for my 1971 Evinrude 50hp suggests the low speed screws should default at 5/8 of a turn out. Then fine tune from there. Mine idles very well at that setting. What kind of shape are the needle tips?

 

[jsrock563]

Re: 1971 Johnson 50ESL71S Carburetor Adjust Pointers

Both cylinders are firing with new plugs installed. The needles are in excellent condition with new teflon inserts installed. I decided to rebuild the carbs, because the engine had been sitting for some time. Originally, it would not idle on its own. I had to hold the throttle and choke it by hand in order to keep it running, and was amazed at how clean it appeared to run (hardly any smoke and no soot). The engine has dual carbs, each with a single needle adjust. After cleaning the carbs the engine now starts easily and will idle on its own, but I've noticed it smokes a lot more than it did before. So far, all adjustments have been made with the mouse ears attached and not in the water. I was prepping it before I put it back in the water. Thanks.