Evinrude great power / crapo power / repeat

[MAW31]

Evinrude/Johnson 110HP, 1994

started motor, heading out slow wake speeds. motor still cool, motor kicks in strong for a period, then just drops back to crapo running, like its on 3 cylinders, then pops up to smooth strong running, then rpm drops down, head shakes more. all at no certain interval. so far all at idle speeds mind you.

got out to bay, goto WOT, motor does not have jump it usually has, but slowly climbs to a plane with a pretty good head shake. (18ft CtrCon, 1/4 tank, just me, no gear). RPM climbs but wont go rpm past 4k. (usually hits 5700)

then...at any undetermined time, BAM...full on power like someone hit a switch, sometime later, motor drops back into sluggo mode through all rpms, just like when it did at no-wake speeds.

I disconnected the temp sensors did another run with same results. keep in mind that the on then off power seems completely random.

Drivin me nutz.

Things I observed:

all 4 spark wires are firing (timing light check on each wire)
good charge while running (14V)
did a static advance test. 24BTDC. ok.
spark plugs are Champion as defined in manual and 2 weeks old.
visual check on water via pee stream. ok.
both carbs were taken off and cleaned in April. (just maintenance)

about the only thing i have not replaced is the power pack and i dont know if theres a reliable test for that, but i'm about to replace it by default.

I've got the motor up on davits ATM, so i'll test out any ideas you come up with.

thanks

 

[riverrat45]

Re: Evinrude great power / crapo power / repeat

could you or anyone else run into some sand this could be lodged into your thermostat holding it open causing engine to run cold and poor fuel burn
check plugs again for fouling
had similar issue
rr45

 

[j_k_bisson]

Re: Evinrude great power / crapo power / repeat

You may be getting a weak spark from a weak power pack. The proper way to check this for sure is to pick up a spark gap checker at any auto story. Set the gap to 7/16" you should see a bright blue flame/spark. If not then you are getting a week spark. Even though you get a reading does not mean it is enough to fire the cylinder.

 

[FUL_005]

Re: Evinrude great power / crapo power / repeat

Just saw this thread today, and I know its a few months old, but what you have described is exactly what is happening to my late Eighties 70hp Evinrude. It is also driving me nuts too. You just dont know how it is going to behave on any given day, or, hour of the day. I has hoping you found the solution and could share it with me, because I have had so much conflicting advice on what the problem is caused by. I have been searching the internet for a similar problem and you have decribed it perfectly. Most of the time it runs like a dream, 6000 rpm WOT and 55kmh. But you never know for how long. It always seems to be when your racing a storm front back in!! This is making me reluctant to go out. I know Carbies, compression, Tanks, fuel are all good as I have had them checked and replaced. Please let me know, as I think it will only get worse and do it more often. Thanks Heaps.