"Todd.... A word of caution, n
"Todd.... A word of caution, never NEVER allow your engine to obtain high rpms when in neutral. You could very easily encounter a runaway engine, and should that happen (and it does), by the time you gathered your thoughts, that engine would blow a couple conecting rods right through the side of your engine!
The rapid, I assume instantanous increase of rpm from 4500 to 5400, rather than a gradual up and down type surge, spells out ignition. The fact that you're encountering a difference of 900 rpm would indicate that one cylinder is dropping out (9x6=54).
Carburetors, if fouled, do not come and go, they stay that way. And if the problem was fuel related (air leak, fuel restriction), that always (has been my experience anyway) results in a gradual decrease and increase of rpms. You could test the fuel theory easily by simply pumping the fuel primer bulb, acting as a manual fuel pump.
Ignition on the other hand, can be quite intermitent. I suggest that you start at the beginning to trouble shoot the problem as follows.
(General Engine Checks)
First, check the compression. It should be approx 100+ psi and even on all cylinders. On some V/6 looper engines, 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.
NOTE... If checking the compression with the spark plugs in, 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.
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 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.
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 few 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. (I seriously doubt that this is your problem).
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. (You might want to check this on general principles). Let us know what you find.
Joe
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