1991 Johnson 90, Misfire and Erratic Idle. - Moderated Discussion Areas

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  1991 Johnson 90, Misfire and Erratic Idle.

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Author Topic:   1991 Johnson 90, Misfire and Erratic Idle.

mcole posted 03-31-2014 02:07 PM ET (US)
I have a 1991 Johnson 90 that is eating me alive. The symptoms are that it will not idle, it misfires.
I conducted a cylinder balance test. The left bank of cylinders, #2 and #4 there is no change in RPM. There is very strong spark on all four cylinders.
Engine is non VRO.
What I have done so far: Carbs rebuilt, all new fuel lines, pump and filter, fresh gas 50:1.
New ignition coils, spark plugs and wires.
DVA tests of the stator are as follows:
Between brown and brn/yel is about 380 volts (connector disconnected). If i reverse the DVA meter leads it drops to 220 volts.
DVA at orange ignition coil leads (back probed )
180 volts on all four
Stator resistance is about 500 ohms.
Timer base is 0.6 volts DVA from white to all other colors.
Timer base resistance is about 40 ohms from same wires.
Removed flywheel and checked for cracks. It looks great.
Replaced power pack with OEM OMC unit. No change.
Compression is 120-PSI on all four holes warmed up and at WOT.
Carbs are clean as a whistle.
Replaced port head gasket for the hell of it. Looked perfect inside.
I was a prior marine mechanic for over 10 years and am now in LE.
Anyone have any insight for me? I have just about every tool and piece of test equipment.
Mike

mcole posted 03-31-2014 02:12 PM ET (US)
Also the engine needs lot of choke to get running.
jcdawg83 posted 04-01-2014 08:57 AM ET (US)
I'm not a mechanic, but the need for choking and the idle problem really sounds like a fuel delivery problem to me. I honestly don't know what more you can do, it sounds like you've replaced everything that can be replaced without an engine rebuild.
Will it run at higher rpms? If so, could it be a low speed carb jet issue?
mcole posted 04-01-2014 09:02 AM ET (US)
Yes it runs just fine at higher RPM. I have pulled carbs 3 times and gone through them with a fine tooth comb. I even swapped them with a know good set of carbs. No change.
jcdawg83 posted 04-01-2014 10:04 AM ET (US)
Good luck; if it's electrical in nature, that's my Waterloo. I know nothing about the electrical/ignition system, it's voodoo to me.
I know you've checked all connections and grounds, that is my only idea when it comes to electrical issues. What do the manuals say the volts should be and are they in the proper range?
adlert posted 04-04-2014 01:40 PM ET (US)
Just to be absolutely clear mcole, when you say your engine is running "fine" at high speeds, you are saying that your are hitting your normal wide open throttle rpm and speed range?
contender posted 04-04-2014 05:55 PM ET (US)
sounds like one of your low speed jet is clogged. These years evinrude and johnson were bullet proof, If your engine is in good shape its something simple. Are your parts all factory parts or did you go aftermarket? Are you spark plug wires real wires or are they the carbon crap? Are you running AC plugs (autolite seem to not work correctly in Johnrudes)...I would have to be there to see whats happening for other ideas, sorry...good luck
adlert posted 04-06-2014 12:31 PM ET (US)
I have some thoughts mcole. Just waiting to see if you are still here and having the problem before typing things out.

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Author	Topic: 1991 Johnson 90, Misfire and Erratic Idle.
mcole	posted 03-31-2014 02:07 PM ET (US) I have a 1991 Johnson 90 that is eating me alive. The symptoms are that it will not idle, it misfires. I conducted a cylinder balance test. The left bank of cylinders, #2 and #4 there is no change in RPM. There is very strong spark on all four cylinders. Engine is non VRO. What I have done so far: Carbs rebuilt, all new fuel lines, pump and filter, fresh gas 50:1. New ignition coils, spark plugs and wires. DVA tests of the stator are as follows: Between brown and brn/yel is about 380 volts (connector disconnected). If i reverse the DVA meter leads it drops to 220 volts. DVA at orange ignition coil leads (back probed ) 180 volts on all four Stator resistance is about 500 ohms. Timer base is 0.6 volts DVA from white to all other colors. Timer base resistance is about 40 ohms from same wires. Removed flywheel and checked for cracks. It looks great. Replaced power pack with OEM OMC unit. No change. Compression is 120-PSI on all four holes warmed up and at WOT. Carbs are clean as a whistle. Replaced port head gasket for the hell of it. Looked perfect inside. I was a prior marine mechanic for over 10 years and am now in LE. Anyone have any insight for me? I have just about every tool and piece of test equipment. Mike
mcole	posted 03-31-2014 02:12 PM ET (US) Also the engine needs lot of choke to get running.
jcdawg83	posted 04-01-2014 08:57 AM ET (US) I'm not a mechanic, but the need for choking and the idle problem really sounds like a fuel delivery problem to me. I honestly don't know what more you can do, it sounds like you've replaced everything that can be replaced without an engine rebuild. Will it run at higher rpms? If so, could it be a low speed carb jet issue?
mcole	posted 04-01-2014 09:02 AM ET (US) Yes it runs just fine at higher RPM. I have pulled carbs 3 times and gone through them with a fine tooth comb. I even swapped them with a know good set of carbs. No change.
jcdawg83	posted 04-01-2014 10:04 AM ET (US) Good luck; if it's electrical in nature, that's my Waterloo. I know nothing about the electrical/ignition system, it's voodoo to me. I know you've checked all connections and grounds, that is my only idea when it comes to electrical issues. What do the manuals say the volts should be and are they in the proper range?
adlert	posted 04-04-2014 01:40 PM ET (US) Just to be absolutely clear mcole, when you say your engine is running "fine" at high speeds, you are saying that your are hitting your normal wide open throttle rpm and speed range?
contender	posted 04-04-2014 05:55 PM ET (US) sounds like one of your low speed jet is clogged. These years evinrude and johnson were bullet proof, If your engine is in good shape its something simple. Are your parts all factory parts or did you go aftermarket? Are you spark plug wires real wires or are they the carbon crap? Are you running AC plugs (autolite seem to not work correctly in Johnrudes)...I would have to be there to see whats happening for other ideas, sorry...good luck
adlert	posted 04-06-2014 12:31 PM ET (US) I have some thoughts mcole. Just waiting to see if you are still here and having the problem before typing things out.