Re: BOB any way to test 75 johnson on muffs
It would help if you had listed the year of the engine you'll be looking at, however the following should take it all in.<br /><br />(General Engine Checks)<br />(J. Reeves)<br /><br />First, check the compression. It should be approx 100+ psi and even on all cylinders. On some V/6 looper engines (1986-87), the starter bendix will kick out if all of the spark plugs are removed. If this takes place, leave the spark plugs in, excepting the cylinder you're checking of course.<br /><br />NOTE..... If leaving the spark plugs in while you're checking the compression (V/6 Loopers), make sure that the ignition key is in the "OFF" position. You do not want that engine to start while you're doing that test. <br /><br />Next, with the s/plugs removed, check the spark. It should jump a 7/16" gap with a strong blue flame on all cylinders. (The s/plugs must be removed in order to obtain the highest rpm available). On engines 1972 and older, and engines without solid state ignition, set the tester gap to 1/4".<br /><br />Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.<br /><br />Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.<br /><br />Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. Poor or no continuity of a coil is one reason for s/plug fouling.<br /> <br /> - - - - -<br />NOTE..... For the older magneto ignition coils, the continuity check would be as follows:<br /> <br />Checking the continuity of the ignition coils....... Have the ohm meter set to High Ohms.<br /><br />Remove the primary wire from points. Remove the coil ground wire. You do not want either of these wires touching anything.<br />Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground wire of the coil.<br /><br />Then touch (still with the red lead) the primary wire. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. <br /><br />If there is no continuity between the secondary circuit (spark plug) wire and the primary or ground, remove the coil from the armature plate, then check the continuity directly between the prong within the coil (prong that the plug wire connects to) and the primary and ground. Poor or no continuity of a coil (or plug wire) is one reason for weak spark, s/plug fouling, or no spark.<br />- - - - -<br /> <br />When removing the spark plugs, make a note of which s/plug came from what cylinder. They should all look alike, but if not, that difference should lead a mechanic in a certain direction.<br /> <br />Remove the spark plugs, then insert a screwdriver or some such object into the cylinder, and have it rest on top of the piston. Do not apply pressure to the screwdriver yet. You simply want to know where the piston is. Now, turn the flywheel by hand and get the piston to come up to dead top center, then drag it down about 1" by turning the flywheel. Now, hold the flywheel tightly and apply pressure to that screwdriver or whatever object you're using. If you can move that piston without moving the flywheel, that indicates that there is play in either the wrist pin area or at the crankshaft to connecting rod area. <br /><br />If the engine has been sitting for any length of time (a couple months or more), there's a very good possibility that the carburetor(s) are somewhat fouled/clogged/gummed. If so, they'll require removing, cleaning, and rebuilding.<br /> <br />Remove the carburetor face plate. Observe the carburetor(s) while you pump the fuel primer bulb. If fuel flows out of the carburetor(s), they will require removing, cleaning, and rebuilding.<br /> <br />(With Engine Not Running) Check that the throttle plate butterflies are opening full (horizontal) when full throttle is applied. Also check to see that the timer base under the flywheel is advancing to the full spark advance point, up against the rubber cap of the spark advance stop screw.<br /><br />At the lower portion of the lower unit, there will be a large slotted screw. Loosen that screw to see if the unit has good lube, and to check for metal filings and water. Small fuzzy filings is acceptable. Sliver and/or splinter type slices/chips of metal are not! Water would indicate that the unit has faulty seals. The lower unit requires filling from that large slotted bottom screw until the lubricant flows out of the like screw higher up in the lower unit. Should your engine have a philips screw located in the skeg, do not remove it as that is a shoulder bolt type screw that is actually a pivot point for a internal shift lever.<br /> <br />Check, while under way, that the engine engages both forward and reverse properly, and that the engine does not jump out of forward gear at a high rpm.<br /> <br />If the engine is on a boat, check the steering to make sure that the steering rod moves in and out freely, and that the engine swivels freely in even degrees in each direction.<br /> <br />When running the engine, pulling each s/plug boot terminal off of the s/plugs should result in a even rpm drop through out.<br /> <br />Check that the PTT assy runs the engine up and down smoothly... and that it doesn't drift down on its own.
<br /><br />Some additional things I wanted to add. You can profit from the mistakes I made:<br />* Get the model number of the engine and research it out. Find out the configuration of the engine, how many power packs, type of fuel pump, etc. You'll have a better idea of what you're looking at when you pop the cowling, plus you'll be able to tell if any major changes were made to the engine. (My model number apparently doesn't exist) 
