"Jim.... First, check the comp
"Jim.... First, check the compression. It should be approx 100+ psi and even on all cylinders. 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)
Check the continuity of the ignition coils. Remove the primary orange wire from the powerpack. 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. If you know which cylinder is failing, pay particular attention to that coil.
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.
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.
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.
If the engine has been sitting for any length of time (a month 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.
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.
When running the engine, pulling each s/plug boot terminal off of the s/plugs with insulated pliers should result in a even rpm drop through out. Let me know what you find.
Joe (30+ Years With OMC)"
