Re: 1988 Evinrude 70hp help
Start over from scratch to possibly avoid overlooking the obvious. Don't simply assume that since you checked something in the past that it is okay and bypass it.
Build the following spark tester.
(Spark Tester - Home Made)
(J. Reeves)
A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.
Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:
..........X1..........X2
.................X..(grd)
..........X3..........X4
Now, with the spark plugs removed, check the spark while slowly advancing the throttle. The spark should jump a 7/16" gap with a strong blue lightning like flame throughout the advancement.... a real SNAP! Does it? If not exactly as I've described the spark, what are you seeing?
The 120 psi compression on all cylinders (if that is indeed what you have) is fine.
The new spark plugs should be Champion QL77JC4 plugs, gapped at .040 . If this is not what you have, change them.
I know your present spark plugs are new. However, when you remove them, do they all look alike, and if not, describe them.
Engine NOT running, in normal upright running position, carburetor face plate removed. Pump fuel primer bulb up hard. There should be NO fuel leakage at any carburetor. Is there any?
The carburetor throttle roller should be approximately 7/16" in diameter. If it is instead something like 3/16" or 1/4" in diameter, the clear outer shield of it has cracked and broke away, in which case, replace it.
The idle air bleed slow speed jets at the top front of the carburetors should have a ID of .033 . The jet would have the number of 33 imprinted upon it. This jet must be absolutely tight.
The high speed fuel jet, located in the bottom center of the carburetor should have a ID of .065 . This jet would have the number of 65D imprinted upon it.
Make sure that all of the carburetor gaskets are in place, particually the small round nozzle gasket (332708) between the top body and the float chamber.
I see no mention of you actually removing and cleaning the carburetor(s). Your problem may simply be a clogged jet, but if a high speed jet, this would contradict the fact that the engine actually fires okay at a higher rpm.
The throttle butterflies should open and close at the same time. At idle, there should be no pressure applied on any linkage that would create a scenario whereas possibly two butterflies would be completely shut and one ever so slightly open etc.
If a reed plate (leaf valve) was cracked/broken, the downward throw of the piston would force a fuel spray out thru the carburetor throat. This would be noticable at cranking speed possibly and quite noticable when running.
With the above areas being as they should be, and with the engine running at a rpm where #3 (bottom) cylinder is not firing, stick two fingers into the carburetor throat, actiing as a manual choke. If the rpms increase and the engine smooths out somewhat, something is being overlooked within the carburetor.
Let us know what you find.
