Obsolete Outboards

by Max Wawrzyniak - St Louis, Missouri - USA Bringing a 1956 Johnson 15 hp Back to Life Part VI: Reinstalling the Magneto and Carb

Part 1 - Part 2 - Part 3 - Part 4 - Part 5 - Part 7

When we last visited the 1956 Johnson 15, the carb had been cleaned and assembled with a rebuild kit, and the magneto had been assembled with new ignition points and condensers, and also new spark plug wires and/or coils if those had been required. Time to reinstall these (2) major components onto the motor itself.

The carburetor is reattached to the intake manifold using the (2) studs and nuts that bolt through it's flange. There was an old gasket between the carb and the manifold that probably could be reused, but your rebuild kit will have a new gasket. In fact, you will probably find that your rebuild kit has SEVERAL new gaskets, all of which are similar except that the diameter of the big center hole is different in each one. Match up your old gasket to one of the new ones, or if you no longer have the old gasket, use the new one with a center hole of about the same diameter as the carb throat diameter. The reason for all the different gaskets is that the same rebuild kit can be used for several different engines and so extra parts are included. If you don't have a new gasket you can reuse the old one if it is in good condition. I used to smear a bit of gasket sealer on old carb mounting gaskets but I don't bother anymore. The nuts on the carb mounting studs should be torqued (tightened) to a specific inch-pounds specification, but since you are not going to bother with a torque wrench just get them pretty tight without twisting the darn things off. You are dealing with soft aluminum castings here so don't overdo it.

The new carburetor-mounting gasket is in place and the new fuel hoses are being installed. Note the "follower". On the larger engines it is usually a rubber roller; smaller engines use just a piece of round bar (no roller). (click images to enlarge)

Once the carb is bolted on, it is time to run the new fuel hoses. There is special marine- grade fuel hose available and it is good stuff. There is also common automotive-grade fuel hose available at auto parts stores, and it is cheaper. I use the auto. grade hose and have yet to have any problems. I am not recommending that you use what I use: you are responsible for your own actions and decisions. I also like to use clear hose because it allows one to see what is going on with the fuel system, but genuine clear fuel hose is rather expensive. If you try using the cheap clear vinyl hose available at many hardware stores you will find that is hardens with exposure to fuel and is only good for a few months: I recommend against using it.

An outboard motor that uses a pressure tank will have (2) hoses clamped to the quick connect fitting on the motor. The hose attached to the hose barb on the fitting marked "air" goes to the hose nipple on the intake manifold below the carb. The hose that attaches to the hose barb on the fitting marked "fuel" attaches to the hose barb on the carburetor bowl. Pretty simple. Use good hose clamps; the ones that came with the engines were simple little wire "squeeze" types that are a pain in the butt to remove and replace. See if you can get some tiny little worm-screw hose clamps at the auto parts store when you pick-up the auto-grade fuel hose (yeh, like I really thought you would buy the marine hose.) There are also plastic "one-use-only" clamps available, but in order to remove them you have to cut them, so they are not reusable and you had better get spares.

Some really, really cheap individuals have been known to clamp fuel hoses with ordinary plastic wire-ties. These do not work well and are definitely not recommended.

Engines fitted with fuel pumps are a little more complicated to "plumb" but still not a big deal. The quick connect fitting has a single hose barb; the hose from the fitting connects to the intake side of the fuel pump (the pump will be marked in some manner.) A hose is then run from the output side of the pump to the carburetor. If your fuel pump is direct-mounted to the transfer port cover of the engine, then that is all there is to it. If, however, you are using a pump that receives it's pressure-vacuum pulsations through a hose, such as was used in the fuel pump conversion column, you will also need to run the pressure/vacuum hose. You can probably use the same hose but keep this in mind: in the pressure tank engines all hoses are under pressure, while on a fuel pump engine the supply hose to the pump is under vacuum; the discharge hose from the pump is under pressure, and the hose supplying pressure/vacuum to the pump (if a hose is used) is alternately under pressure and vacuum. Make sure that the hose you use in a vacuum application can handle the vacuum without collapsing.

Instructions for synchronizing the magneto advance to the carburetor throttle butterfly valve. Note the comment that the choke needs to be in the "off" position while making this adjustment.

Most of these old OMC outboards were fitted with a fuel strainer and a glass sediment bowl. Sometimes the strainer/bowl is an integral part of the carb and sometimes it is a separately-mounted component. If separately mounted, be sure to include the strainer in your fuel line. It is probably best to route the hoses so that the strainer is under pressure (on the discharge side of the fuel pump) instead of under vacuum (on the intake side of the fuel pump). If the strainer is part of the carb, it will be under pressure and you don't have to worry about running a hose to it. Of course, no matter where the strainer is on a pressure tank engine it is under pressure. Your rebuild kit kit should have a new gasket for the glass strainer bowl. The actual strainer element within the bowl is sintered bronze or something like that and is cleanable and reusable. Give it a good spraying with your can of carb cleaner (use eye protection.)

I also like to use a small "in line" fuel filter in addition to the original-equipment fuel strainer. The Sierra brand 18-7828 filter is compact and made of clear plastic (so that you can see what is going on) and is the filter that I always use. It is for 1/4 inch hose, but I use it on small er hoses by either dipping the end of the hose in boiling water for a moment in order to soften the hose enough to slip the hose onto the hose barbs, or I just put a drop of oil on the hose barbs and force the hose on. The hose I use has been able to stand up to this mistreatment but cheap hose may split. I leave any hose that forced onto the filter a bit long so that a half-inch or so can be cut-off when a new filter is installed. I also always install the in-line filter on the discharge side of the fuel pump on those outboards so equipped, so that the filter is under pressure and not vacuum. Note that most of these filters have an arrow on them indicating the direction in which fuel should flow through the filter.

Again, use good hose clamps. While a leak under pressure will be obvious, a vacuum leak in the fuel system of a fuel pump-equipped engine can be a frustrating problem to trouble-shoot. Use new hoses and good clamps and head-off any vacuum problems. Vacuum leaks suck (sorry).

With the carb bolted on and the hoses installed, you can now install the magneto. Set the mageto down over the crankshaft while being sure that you have the front of the magneto to the front of the engine. The sheet metal "ramp" or "cam" should be over the carb. It will be necessary for you to hold the ignition points in the "open" position so that the spring-loaded arms will clear the cam on the crankshaft that the arms ride on. Take your time. The four screws that hold the magneto on need to be lined-up properly with the holes in the metal ring under the magneto. Make sure you are not pinching the spark plug wires. Once screwed-down, the magneto should rotate back and forth smoothly: this is how the "spark" is advanced. Re-attach the little bellcrank (lever) on the Port side of the motor that connects the twist-grip throttle to the magneto.

You are now ready to "synchronize" the magneto to the carb. When you twist the "twist grip" on the tiller, the magneto rotates back and forth. There is a linkage from the carburetor "butterfly" throttle valve that has a "follower" (either a rubber roller or just a piece of round bar) that rides along that cam on the magneto. As the magneto rotates, the follower rides up the incline on that cam and in turn opens the carb. throttle butterfly valve. In order for the engine to run properly, the butterfly needs to open at the correct time. The cam is attached to the bottom of the magneto with two small screws, one of which has a slotted (oversized) hole. The cam will also have an index mark, either a line or an arrow, on it's upper face. Loosen (but do not remove) the (2) screws holding the cam, and adjust the position of the cam so that the carb butterfly starts to open at the instant that the follower is aligned with the mark on the cam. Keep in mind that there is a bit of "slack" or looseness in the linkage that couples the follower to the butterfly shaft: the slack should be all "taken-up" and the butterfly shaft itself should just start to rotate when the follower is aligned with the mark on the cam. Then tighten the cam mounting screws and re-check to be sure nothing has changed.

The "adjuster" for setting the gap looks like a screw but it is not. It is permanently attached to the magneto. The adjuster is rotated back and forth to adjust the size of the points gap. Very very VERY tiny movements of the adjuster make a big difference in the point gap.

It is now time to "set the points." What you are going to do is to adjust how far the ignition points open. OMC (Outboard Marine Corp, the manufacturer of Johnson, Evinrude, & Gale outboards) made special timing tools which were used in conjunction with a test light for this purpose and I have a set of those tools but never use them. What I use is a set of "feeler gauges," available at a cost of a couple bucks at any auto parts store or most discount stores. You will need one with leaves measuring .018, .020, & .022 inches in thickness. All feeler gauge sets that I have ever seen have these sizes so that other than avoiding a metric set (unless you want to make the conversion) you don't really need to buy anything but the cheapest set you can find.

The rocker arms of the ignition points ride on a cam on the crankshaft, As the crankshaft spins, the lobe of the cam opens and closes the points. Roll the crankshaft around by hand until the tiny plastic rubbing block on the rocker arm of one of the points sets is aligned with the key (The metal thing that locks the cam and the flywheel to the crankshaft so that they don't spin loosely on the crankshaft.). I usually remove the spark plugs (assuming they are not already out), put the engine into forward gear, and roll the engine around with my foot on the propeller. Or, you can thread the crankshaft nut down onto the crankshaft and use a wrench to rotate the crankshaft. Slightly loosen the single mounting screw on the points set base plate, and then slowly rotate the adjuster back and forth while holding the .020 leaf of your feeler gauge in between the contact surfaces of the points. You want to feel a very slight "drag" when inserting and removing the .020 leaf into the gap. Pushing the .020 leaf in should not spread the points open even a minute amount, nor should the leaf "rattle" back and forth between the points contacts (even a tiny amount.) You want a barely perceptible"drag." When you have that, tighten the mounting screw and check it again to see if the setting changed any ( it probably did, and you will probably have to re-do this two or three times before you end-up with the barely perceptible drag after tightening the mounting screw). The tighter you can leave the mounting screw while making your adjustments, the less likely the setting is to change when the screw is finally tightened.

Using my finger to hold the contact surfaces of the points open; you will be using your feeler gauge between these (2) surfaces. This is also how you hold the rocker arms back when installing the magneto on the engine. The points are spring-loaded to the closed position. Note the rubbing block that rides on the cam on the crankshaft.

If you have the mounting screw tightened and you are happy with the "drag," then try inserting the .018 leaf into the points gap: it should "rattle" back and forth a tiny amount. And when you try inserting the .022 leaf it should be necessary to slightly force the leaf into the gap.

Now rotate the crankshaft 180 degrees until the key on the crankshaft is lined-up with the rubbing block on the rocker arm on the other set of points and go through the whole process of setting the other points, Then rotate the crankshaft until the key is again aligned with the rubbing block on the first set of points and check it again. Then check the second set of points again.

Perhaps more critical than the exact gap of the points is that both sets of points be set as exactly alike as possible. OMC said that new points sets could be set @ .018 if desired while .020 was recommended for setting the gaps of existing points; I set all of mine to .020 whether I have just installed new points or are adjusting old ones.

Using a screwdriver to make tiny TINY movements on the adjuster while checking the gap with the .020 leaf of the feeler gauge.

Finally those little cyanide capsules I mentioned way back months ago? They contain a bit of grease. The purpose of the grease is to lubricate the rubbing blocks on the points rocker arms so that the plastic rubbing blocks do not wear excessively which would change the gap setting of the points. You engine originally came with a little felt wiper which rode on the cam; if you wish you can apply a drop or so of grease to that wiper. Often ,however, the wiper felt is missing. I have never applied this grease to any of the engines I have ever worked on. Every few years I give them a tune-up which would include at least a gap re-setting which may be why I never have a problem with rubbing block wear changing the point gap. It's up to you. You can apply the grease (very sparingly) if you wish, or you can "toss" the cyanide capsules and not worry about it. I don't know too many people who run their outboards enough hours to make rubbing block wear a serious concern. Again, use VERY little grease if you use it: grease spun-off the spinning cam can raise havoc if it gets on the contact surfaces of the ignition points. I once spent a considerable amount of time trying to trouble-shoot an outboard that would run good at idle speed, but as I advanced the throttle, if would stumble and cough and hardly speed-up at all until I got to full-thottle, at which point the thing would suddenly "wind-up" and about throw me out of the boat. After much time spent cleaning and rebuilding the carb and adjusting the gaps of the existing points, I finally discovered a tiny drop of grease/oil on one set of points, Replacing both sets of points had the engine running like new.

Next time we reinstall the flywheel and see if the darn thing will run.

Happy Motor'n
Later,
Max

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