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by Max Wawrzyniak - St Louis, Missouri - USA

Bringing a 1956 Johnson 15 hp Back to Life

Part V: Carburetor Work,
and a Few Words on Fuel

Part 1 - Part 2 - Part 3 - Part 4 - Part 6 - Part 7

Although we had the magneto ready to reinstall last month, I usually suggest that one wait until the carburetor (carb) work is done before reinstalling the magneto. Although the carb can certainly be removed and reinstalled with the magneto on the engine, leaving the mag off gives one a bit more room to work.

Before we get into the carb, however, we need to discuss some late-breaking developments in the gasoline situation. As most residents of the USA are probably aware, refineries are discontinuing the use of an gasoline additive known as MTBE in favor of another additive known as ethanol. The August/Sept. issue of Professional Boatbuilder Magazine has a very cryptic article concerning the problems that this "reformulated" gasoline is causing in both old and new marine engines. As of this writing (Sept. 2006) this issue of Pro. Boatbuilding can be accessed online HERE. (if there is a newer issue showing, try the "Archives" for the Sept/Oct 2006 issue - Ed)

A quick summary of the problems that reformulated gasoline containing ethanol is causing in boats: The ethanol is literally dissolving fiberglass fuel tanks, which had previously been considered to be a high-quality alternative to corrosion-prone aluminum and steel gasoline tanks. Some very expensive production boats built by top-line builders may require very expensive tank replacement. Plastic tanks, such as the common portable tanks used with outboard motors, are fine as long as they are in good condition.

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No caption needed.

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Another problem is that the ethanol can absorb a very large amount of water, and if the water is allowed to settle to the bottom of the tank and then drained or pumped out, the ethanol component of the gasoline will stay combined with the water and will also be removed from the tank, leaving one with gasoline that is missing a major part of it's chemical make-up. The article mentioned suggests that one ALWAYS use a non-alcoholic fuel stabilizer, at ALL times. Gasoline now just does not have the "shelf life" that it used to, so try to avoid storing gasoline for months at a time and always protect the tanks from water intrusion while being aware that the ethanol can absorb humidity from the atmosphere as well.

And it is getting more difficult to check for water in one's gasoline tanks. For years I have advocated the use of "water finding paste;" one smears a bit of the paste on the bottom of a stick, pokes the stick into the gasoline tank, and if the brown paste turns purple, there is water in the gasoline. I have been using the same tooth-paste-size tube of "Kolor Kut" water finding paste for over 15 years (no kidding !) but have now been informed that it will not detect water combined with ethanol. I now need to buy a new tube of Kolor Kut especially formulated to detect water in ethanol-laden gasoline (figure SF 32).

Ethanol is dissolving varnish and other "gunk" that was once considered to be more-or-less permanent in the fuel system, resulting in plugged fuel filters and plugged carbs. It is more important than ever to have good fuel filters and water separators in one's fuel system. My habit in the past was to utilize the glass-bowled filter/separator that was usually factory equipment on old OMC outboards, and in addition to install a clear plastic "in-line" filter in the fuel line under the engine cowl. Time will tell if I need to modify that arrangement. I should add that I always carry spares for the disposable in-line filter. Try to start out with as clean a fuel system as possible.

Plugged passages are the most common problems one will encounter with carbs.

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It should go without saying that all fuel hoses should be replaced. This means the hoses under the engine cowl as well as the hose to a remote tank. And the use of a rebuild kit for the carb with new gaskets is always a good idea. The Sierra brand carb kits I usually use also come with a very nice set of instructions (figure SF 36).

A question still unanswered is how ethanol will affect the varnish coating on the cork carburetor floats. For the time being I intend to "run the gas out" of my engines when done boating for the day in order to minimize exposure to the ethanol, although running the gas out does not totally drain the float bowl of fuel.

One more note: in the column on converting outboards to use a fuel pump instead of a pressure tank, I recommend the use of a hard-setting gasket sealant for sealing passages that are not needed. I have a report from a reliable source that the gasket sealant dissolved,
possibly due to ethanol exposure. Apparently J B Weld will hold up to the ethanol better, but might make a later conversion back to the pressure tank more difficult, if that is a concern.

Getting back to the job at hand: The carb is held on by (2) nuts, but before you loosen the nuts have a look at the linkage from the carb throttle "butterfly" shaft up to the magneto plate. When you twist the "twist-grip" throttle, you are actually rotating the magneto (stator) plate back and forth, which advances and retards the ignition timing. This action alone will cause the engine to speed-up and slow down, and I have a few very old outboards where advancing and retarding the magneto timing is the primary means of "throttling" the engine. The engine will run smoother and more efficiently, however, if the flow of fuel and air mixture to the engine is varied to match the needs of the engine at a particular throttle setting. To accomplish this, most of the older OMC outboards of less than 35 hp have a sheet metal "cam" or "ramp" on their forward side which moves a "follower" that opens the throttle butterfly though a linkage. On some engines, this linkage of levers and bell cranks is attached entirely to the carb and one need not mess with it when removing the carb. On other models it will be necessary to disconnect the linkage in order to remove the carb. On these latter engines, usually loosening a set screw on a bell crank, or removing a tiny cotter pin from an arm, will disconnect the linkage. Figure SF 35 shows where I disconnected this linkage on the 1956 15 hp Johnson. Another item needing to be removed is the fuel hose to the carb from the fuel pump, or from the "quick connector" on pressure tank engines.

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A less "cluttered" look at the typical carb found on old OMC outboards.

The 1956 Johnson has a "face plate" over the front of the carb that is held in place by the knobs or levers used to turn the high - and low speed needle valves. Similar vintage Evinrudes did not have this separate face plate. Later model engines with the "one-piece" fiberglass hoods will have other arrangements of knobs and/or levers for controlling the high- and low speed needle valves, and engines manufactured after about 1963 will have a low speed needle valve but the high speed needle is replaced with a fixed "jet " (orifice ) that is not adjustable. To remove the carb from a particular engine may require you to disassemble some or all of these linkage arrangements. Be sure to take good notes and maybe a few photos to help when it comes time to reassemble everything. Once this "gingerbread" stuff is out of the way, the carbs are all really very similar.

On the '56, I was able to remove the carb with the face plate and the air silencer intact as shown in figure SF 37. The air silencer is sometimes mistaken for an air cleaner but very few old outboards were fitted with air cleaners. Just a side note here: a modern outboard fitted with fixed jets, when run without the restriction of it's factory-fitted air silencer, can get too much air and run lean and hot. Don't run modern outboards with the air silencer removed, unless the carburetor has been "re-jetted" to handle the extra air flow.

All we are going to do to the carb is to clean it, replace a few parts and gaskets, check and adjust the "float level," and put it back together. Most of the things that can go wrong with the carb involve "clogg" in the tiny passages through which the gasoline must flow (figure SF 33). This cleaning takes me about 10 or 15 minutes: if you haven't done it before it might take you twice as long.

A carb fitted with a high speed fixed "jet" or orifice instead of an adjustable high speed needle valve. The low speed needle remains.

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The first thing I do is to unscrew and remove the high-speed and low-speed needle valves (if your engine is about a 1964 or newer model, you will only have a low-speed needle and a plug were the high speed needle would be - remove the plug)( figure SF 35). Note that there are threaded sleeves that surround the needles that can also be unscrewed and removed. These are the "packing nuts," and behind them is the "packing", which are tiny rings of gasket material. Tightening the packing nuts compresses the packing against the needles themselves and the carb housing and seals the needles, much as a packing gland or "stuffing box" seals an inboard boat's propeller shaft or the valve stem of an ordinary water valve. Remove these
packing nuts and if you can "fish out" the old packing rings that's fine, and if you can't easily get them out that is fine as well.

Next I invert the carb and remove the (5) or so screws that hold the float bowl (bottom of carb) on. Once you have the float bowl off, keep the carb upside - down and carefully remove the hinge pin for the float, the float itself (looks like a doughnut, and probably made of cork unless a plastic replacement has been installed at some point). Also remove the float needle valve which sits underneath the float arm. If you happen to turn the carb right-side up with the bowl off, this needle valve will probably fall out. Also note that the "seat" that the needle valve fits into is made of brass and is removable if you have a "regular" screwdriver with a very wide blade. Since you are following my advice and using a rebuild kit which includes a new needle and seat, you ought to try to remove the old seat. If you strip the tiny slots on that brass seat, however, you have a problem. I have been able to remove these, without the proper wide-blade screwdriver, by using (2) small regular screwdrivers braced against each other in an "X" pattern, with the blade of each driver engaged in opposite sides of the slot. If you tear-up the seat trying this, it aint my fault. See figures SF 35 & SF 38 for a look at the parts you will be dealing with and their locations inside the carb.

click to enlargeThe Sierra kit that I used on the 1956 Johnson 15 hp, part # 18-7043. This particular carb kit fits several different of OMC outboards and contains extra parts such as gaskets in various sizes that were not used on the 15. This kit includes a nice set of instructions with great drawings.

While the carb is still upside down the final object to remove is the high speed nozzle with is usually threaded into the center of the top half of the carb body. Note that there is usually a cork "doughnut" seal around this high-speed nozzle (do not confuse the high-speed nozzle with the high-speed needle valve or the high-speed fixed jet we have already discussed.) You can now safely turn the carb body right-side up if you so desire.

You will note little "welch" plugs (similar to tiny freeze plugs) plugging various holes in the body of the carb. These are to close the holes formed when the carb's inner passages where drilled. The manuals will tell you to remove these welch plugs (which destroys them) in order to property clean passages behind, and then to install new plugs, which are included with the rebuild kit. I almost never remove the old welch plugs, as new ones are hard to get properly sealed without the special tools for installing them, which I don't have. (bet you don't either.) Old manuals also generally recommend soaking the carb body in carburetor cleaner, which is also something I rarely do. I generally use an aerosol carb cleaner, which is what is generally recommended for the mostly plastic carbs found on late model outboards. Aerosol cans of carb cleaner always come with a long thin tube for shooting cleaner into tight places, and I generally spray cleaner into all of the carbs openings in addition to giving the float bowl a good bath to remove any accumulated sediments, and that is usually enough to clean most carbs, although I occasionally run across one so encrusted that soaking in carb cleaner for a couple of days is required.

A word of CAUTION: If you spray cleaner into a little passage on a carb, it will invariably shoot out of another passage right at your face. Wear chemical protection goggles at a minimum! A full face shield is better, and rubber gloves will kept the stuff off your skin - it burns something fierce! You have been warned.

By the way, carb cleaner removes "varnish," and if you have a cork carburetor float it is coated with varnish, so don't let the cleaner get near a cork float.

click to enlargeThe carb on the 15 can be removed with the face plate and air silencer intact although you can certainly remove these items before removing the carb if you wish. Depending on exactly which model of old OMC you are working on, you might need to remove other types of hardware, although underneath it all the carbs are remarkably similar.

With the carb clean, you are ready to reassemble (this is going purty quick, aint it?). With the carb body again inverted (up-side down) you can screw in the new brass seat for the float needle valve - note that there is a little gasket that goes underneath it. The needle valve itself just sits down in the seat but if you check your rebuild kit carefully you will probably find a tiny little wire "hair pin" looking thing. This snaps onto the needle valve and slides onto the sheet metal hinge arm of the float, so that when the carb is right-side up, the weight of the float (and not just fuel pressure) will pull the needle valve down to the open position. Your old needle valve may not have had this little hair pin attaching it to the float.

Next you can install the float by sliding it's hinge pin in - be sure to put the float on up-side down (the carb is also up-side down, remember?). Next comes checking the float level setting.

With the carb upside down, and the float all the way up (which is actually down, since the carb is upside down) the top surface of the float (bottom when upside down) should be flush with the bottom edge (top edge when upside down) of the float bowl.

"Say what??" Yeah, I hear ya; have a look at figure SF 39: One picture can explain it better than I can say it. The Sierra carb kit instructions usually also have a good drawing showing this. You make any necessary adjustments by bending the sheet metal hinge plate on the float (I have always said that these old outboards are "low tech," haven't I?)

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The carb disassembled as far as needed in order to clean it and install the new parts contained within the kit.

Screw the high speed nozzle back into the center of the body in the center of the float, and CAREFULLY push the little cork ring seal over the nozzle.

You can now screw the bottom of the float bowl back on, using the new gasket included in the kit (the kit, intended to fit several different carbs, may have extra gaskets and parts not needed for your particular engine, so in this instance having "extra parts" left-over when you are done is not necessarily an indictment of your mechanical skills).

You can now insert new packing rings into the threaded holes for the high-speed and low-speed needles (if you were able to remove all of the old packing, use (2) or (3) rings; if you left the old packing in, as I do, try adding just (1) new ring of packing. Carefully screw the packing nuts on just a bit (don't tighten them down yet) and then carefully screw the needle valves themselves in. You have to be VERY careful that you do not "bottom-out" the needle valves on their seats, as the needles are soft brass and if their pointy ends are damaged even a little bit, the engine is not going to run well. GENTLY screw the needles in until they BARELY bottom, then back-off one turn. NOW you can tighten down the packing nuts, which will greatly increase the drag on the needles (making if difficult to know if the needles are bottomed-out, which is why we did not do this first.) The packing nuts should be tight enough so that the needles take a bit of effort to turn, so that they will not vibrate and change their settings when the engine is running, and so that there will be no air or fuel leaks around the needles. One potential danger here is that a ring of packing might get underneath the point of a needle valve and block the passage, so use some care.

Setting the float level consists of nothing more than bending the sheet metal hinge tab for the float until the surface of the float is level with, and parallel to, the rim of the carb body. Make sure, however ,that the new bowl needle and seat are in place before you start bending.

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The carb is now ready to go back on, and reinstalling the carb and the magneto will be next month's topic, as will those little cyanide capsules.

Happy Motor'n


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