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Old 25hp Evinrude running problems

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arlenmcgee

New member
Hello, Need some guidance.
Details
Im 63 yrs old
can work on these motors
bought a 1971 25hp outboard, recoil start short shaft model 25102
have ordered a manual, fuel pump, condenser, points, impeller etc from
you guys and am waiting on delivery.
previous owner said new impeller last year
took out last week, started 3rd pull, and ran at top rpm for 3miles with no problems
then at top end engine began throttling down to about 1/4 throttle and would not increase.
I throttled back to idle for about 30 seconds with a mild rough idle then idle smoothed
and gave full throttle and ran great for about 500yds 3-4 minutes or so and then did the
same thing. this repeated for about 5 repeats and I then went to dock.

Bought new 6 gal fuel tank, fuel lines bulb and connectors, put fuel, carb cleaner in new tank
and new fuel. Ran yesterday, not really much difference and ran boat 7-8 miles (1 hour)
Plenty of water is coming from the exhaust port, and finger on cylinder housing, seems to indicate
that water is cooling the cylinders adequately. Have not checked compression yet, will do that today later.
Looking for best guess direction to go in.
thank you
 
Recommended Spark Plug: Champion J4C or J6C gaped at .030

Due to age of engine, coupled with the low quality fuel we have today, I'd personally recommend the J6C plug gaped at .030

Let us know how you make out.
 
Thanks guys,
May not be able to get plugs until Tuesday, Have tried whats open today, Autozone and such, they dont carry and want to
cross reference. Would rather go with champion. whats in engine now is autolite 45R, are they even a marine plug? will keep up with you
until problem resolved. your advice is appreciated.
 
update,
Compression test yielded 110 psi on both cylinders
plugs that were in engine were AC Delco R45, had a new set of same with purchase, put them in with proper gap. of 0.030
found a rub through on the insulation of the lower spark plug lead. Got to get one, but put liquid electrical seal and taped it.
positioned lead so it was away from all arc points. Getting ready to do trial run 3 without engine cover and I am bringing my IR
laser thermometer to shoot cylinders while running. Will post later after get back in couple of hours.
 
trial run 3,
5 miles run to state park harbor, idle in and turned around and came 1 mile back and engine throttled down,
idled 30 sec and back to full throttle, throttled back two more times. Going to try points and condenser when they come in.
I havent drained fuel bowl? yet to see if gunk in it. Oh, the cylinders both ran at 172 to 174 degrees F. the whole time so overheating
isnt an issue. Any other suggestions I would welcome.
 
thanks to all of you guys that responded. They were all good steps to follow.
but the gold star goes to my 84 yr old Dad, he has been saying all along its a
condenser problem. My condensers and points arrived this week and today
I was able to change them out. Took the boat out and the engine ran 15 miles
at full throttle without an issue. Now Im having happiness.
 
Wish I still had my Dad (avatar picture). He was a decent mechanic, but mainly an electrical engineer, he built two TV stations and several radio stations, also an experienced fishing guide in Ontario wilderness. (Once survived a trip down a 50 foot waterfall when his customer's Mercury quit, "water in the gas" ) He ended up saving the life of guy who didn't have on a lifejacket.....and couldn't swim......not a wise combination......plus the guy wanted to fish in this particular area against my Dad's judgement.
If it acts up again we need to focus on a fuel delivery problem. Please keep ethanol out of that motor, please!
 
Last edited:
timguy,
thanks for sharing your story about your Dad, characters make life interesting, sounds like one helluva guy!..Oh the only ethanol that will go near that motor
will be in the form of Jack Daniels going in me!
 
Excellent thinking. Filter ethanol through the liver first. Take the sugar back out, then drain the rest on the ground. Dad did that with a little Johnny Walker, or of course Canadian Club. That's when he ran out of our homemade Zinfandel (dago red).
 
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