1975 Evinrude 25 misfiring continuously on lower cylinder

[vidsdinerie]

1975 Evinrude 25 HP - rope start

​Having trouble finding cause of bottom cylinder dropping out under idle or low load - when I throttle up both fire fine and engine runs smoothly at nearly full throttle this is what have I done so far:

1. Found emulsified oil in top cylinder (spark plug threads and inside cylinder when head pulled) and it would leak emulsified water from weep holes for days and days - resurfaced head and replaced head gasket - Cold compression in both cylinders was 120 psi before and after head gasket changed. Thought this was cause of misfire - it was not. Engine no longer weeping emulsified oil and no emulsified oil found on plug anymore.
2. Removed plugs and checked for sparks while hand cranking - found one cylinder not sparking (do not recall which one)
3. Removed flywheel and check points (points and condenser were replaced last year with Factory parts - <10 hours on them now. Both points in good shape (look new) - checked gap and ok but reset to 0.020 inch per manual on set mark. Magnets on flywheel seem to have good and equal strength.
4. Checked plug for spark and replaced what I though was a bad coil with new - took boat to lake and same problem - misfire unless loaded above slow no wake speed power - Ughhhh!!!
5. Put motor in tank and started engine till problem starts - occurs fairly quickly - removed one coil wire at a time while idling and engine would not on on bottom cylinder - swapped coils so new coil on bottom and repeated test - same problem - will run on top cylinder when lower wire pulled will quickly stall if top cylinder wire is removed.
6. Rechecked point gap and they are still both 0.020 in

Any ideas?

John in Erie.

 

[kbait]

Condenser for bottom cylinder bad? Switch 'em around and see if the problem switches cylinders.

Good luck!

 

[glenn property of pam]

you haven't really proven that the misfire is electrical. Can you borrow a timing light and repeat the tank test then clip the timing light on the spark plug wire to see if its flashing indicating there is or isn't a spark. The reason I says this is a bad seal in the crank case could cause the same type of problem. If it is electrical check the wires under the flywheel are not being rubbed or nicked on a bracket as the timing advances.

 

[vidsdinerie]

Thanks for input - I have a coworker who has a timing light & in line spark tester and will check to see if lower cylinder is sparking - if not sparking I will switch condenser around and see if that is the problem. Will check all the wires as well. This should rule out ignition issues

 

[vidsdinerie]

Ok - just finished with timing light and bottom cylinder is not sparking when it is miss firing. Swapped the coils around again and it is still the bottom cylinder. Decided to remove all the wiring an inspect - its 40 years old and not in good shape - I can still get new wiring (shocking you can still get these!!) but the cost is $50 for both. I decided to order new terminals and just remake them with new wire.

I will swap condensers and see what happens after I remake the wiring - and put it back together. If problem still exists should I replace the coil under the flywheel?

 

[AlTn]

the coil under the f/w supplies voltage to both external coils so if one cylinder is working then the coil under the f/w is fine. That particular ignition setup seems to be sensitive to lightly grounded terminals and coils. I'd make certain that all grounds are made on shiny metal and the terminal connections are tight.

 

[vidsdinerie]

thanks for feedback - pulled all the wiring off and inspected - one section of wire that is inside a "P" clip leading to the the bottom cylinder's condenser/points had the insulation in terrible shape and wire was moderately corroded - removed about 5 inches of wire and replaced with new and put on new ring terminal leading to points - swapped condensers per previous post as well and put it all back together. Found the ground wire leading from the plate to the engine crankcase with a cut as well in the insulation - since that is the plate ground just taped it over. Cleaned the connections and grounds and will try it again hopefully today (weather permitting) and see if that fixed everything. Keeping fingers crossed. Good to know coil is ok

 

[chip's outboard]

1975 Evinrude 25 HP - rope start

Having trouble finding cause of bottom cylinder dropping out under idle or low load - when I throttle up both fire fine and engine runs smoothly at nearly full throttle this is what have I done so far:

1. Found emulsified oil in top cylinder (spark plug threads and inside cylinder when head pulled) and it would leak emulsified water from weep holes for days and days - resurfaced head and replaced head gasket - Cold compression in both cylinders was 120 psi before and after head gasket changed. Thought this was cause of misfire - it was not. Engine no longer weeping emulsified oil and no emulsified oil found on plug anymore.
2. Removed plugs and checked for sparks while hand cranking - found one cylinder not sparking (do not recall which one)
3. Removed flywheel and check points (points and condenser were replaced last year with Factory parts - <10 hours on them now. Both points in good shape (look new) - checked gap and ok but reset to 0.020 inch per manual on set mark. Magnets on flywheel seem to have good and equal strength.
4. Checked plug for spark and replaced what I though was a bad coil with new - took boat to lake and same problem - misfire unless loaded above slow no wake speed power - Ughhhh!!!
5. Put motor in tank and started engine till problem starts - occurs fairly quickly - removed one coil wire at a time while idling and engine would not on on bottom cylinder - swapped coils so new coil on bottom and repeated test - same problem - will run on top cylinder when lower wire pulled will quickly stall if top cylinder wire is removed.
6. Rechecked point gap and they are still both 0.020 in

Any ideas?

John in Erie.

 

[racerone]

Chip-----Your concern ?

 

[chip's outboard]

I had the exact problem with a 1974 25 evinrude someone removed the carb bushing out of the low speed needle, not the one you can see from the front witch is usually red. Probably got blown out by someone cleaning the carb. There is one further in verry small. I could not get the lower cyl to fire at Idle . Just partially it was weak. I replaced the inner bushing and got No#2 back after adjusting the needle and the link from mag to carb. Throttle plate must be closed at Idle even if you have to grind the steps on the mag that interfere with the shift rod detent