johnson sea horse 1958 18hp carburetor ???????

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Erik02c

Cadet
Joined
Feb 28, 2007
Messages
6
Hi, my model is a FD-12 1958 sea horse 18 HP. I rebuilt the ignition system and carburetor except for the carburetor needles. I started her up today and it will not idle correctly. could it be the carburetor needles? I tried to do every adjustment possible on the slow speed adjustment and it ran the best with the needle completely removed from the carburetor. My gas mix is 24:1 and i just don't know what the problem is. Also, if I give it a little gas and get it to idle for a minute or so it almost acts like it has a miss. It will jerk every few secondsor so. Please help me! THANKS!
 
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tmcalavy

Rear Admiral
Joined
Aug 29, 2001
Messages
4,005
Re: johnson sea horse 1958 18hp carburetor ???????

sounds like the idle circuit in the carb is plugge/gummed up. only way to clean them thoroughly is remove, dismantle, soak in carb cleaner (overnight, but don't soak the gaskets or rubbers), blow it out with compessed air and reassemble. To get the base settings for both high and low speed needles do this: remove the screws holding the handles on the needles, turn both needles clockwise gently until they seat/stop (don't over tighten them, back the high speed needle out (counterclockwise) three-eighths of a full turn, back the slow speed needle out one and one-quarter turns. Reinstall the handles: high speed should be pointing straight up, low speed straight down...both should be between numbers 3 and 4 if the decals on the face plate are intact. Now, if someone buggered the needles by overtightening them the taper on the end may be toast. You can check this by removing each needle and checking the taper...it should be smooth, not ridged. If that's the case, time to prowl around for a new/old carb or check with your E-J dealer for a replacement...should still be available. Your gas:eek:il ratio is correct. If it sneezes through the carb before it dies it's running too lean. After you get the baseline needle settings made, start it up and let it idle. Adjust the slow speed gently until you find where it runs best...make note of the setting. Run it up to speed and adjust the high speed needle the same way...better to be a little rich than lean with the high speed needle. These adjustments should be made in the boat on the water for best results.
 
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F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Re: johnson sea horse 1958 18hp carburetor ???????

Did you put in new gaskets? How about the gasket around the brass main nozzle where it sticks into the center of the carburetor bowl?
 
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Erik02c

Cadet
Joined
Feb 28, 2007
Messages
6
Re: johnson sea horse 1958 18hp carburetor ???????

Yeh i put all new gaskets everywhee in the carb. Maybe i didnt get all the gunk out of the needle holes. Thanks for your help guys!.
 
5

58 Johnson

Cadet
Joined
Feb 24, 2007
Messages
13
Re: johnson sea horse 1958 18hp carburetor ???????

Would be interested to know how you fared with this one. I dunno... but I'm thinkin' that if it runs best with the low speed needle right out, there has to be something we're missing. Sounds like it's running too rich... does it accelerate well, or does it bog? I traced the occasional miss and the slight bog in my old 20 (newer but same basic power head) to a bad connection at the spark plug cap that only acted up on acceleration, not even at high speed. An occasional hiccup while idling is very common with old OMC's, but it should not be constant or even regular.

You can set the idle mixture at an idle to get it nice and smooth, but remember to check to see how it accelerates afterwards. Unless the engine is brand new, it is sometimes a trade off. You may not get a perfect idle and the best acceleration. Remember these are old two-strokes that can idle roughly on occasion, especially with such a rich oil mixture and with their relatively low output ignition. If it is idling very smoothly, the low speed needle may be too lean to accelerate quickly. Trial and error!
 
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