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1971 25hp Evinrude running terrible I've done everything I can think of

Sirrobbythe5th

Contributing Member
Hello folks, I recently purchased a 1971 evinrude 25hp sportster and the motor appears to be in great condition. Since the first time I took it out it has been running extremely rough. Almost as if it has fouled fuel, improper fuel=oil ratio, bad spark plugs, or like its being choked out. So I got a new gas can, new hose, inline filter on the hose, new fuel, oil, spark plugs. And it STILL ran rough. So this time I took off the carb in hopes it was a gummed up bowl. Took off the carb to rebuild it and it looks brand new like its recently been rebuilt. So i put it back on, still running like crap. I then took a look at the coil under the flywheel and it looks brand new also. The points and everything looked brand new!!!!!!!! Im stuck here, any ideas? could it be something as simple as timing, or adjustment on the carbs??
 
I will try that. Now when I first got the boat and took it out, it ran great for about an hour or two, when we went to come back in it started running terrible. But now it just constantly runs like crap. However, occasionally it will run normal for a minute or so. Then go back to its antics
 
Now i don't know if this is any help, but my smoke is white ( suggesting I am burning all my fuel ) and my spark plugs are brand new J4c, I plan on getting J6c to help some bit, and brand new spark plugs that are damp ( 2 stoke ) obviously
 
My knowledge here is very limited, On the armature plate there is what apears to be a "coil" and it runs down to two green looking "coils" that are external the flywheel, and have the spark plug leads
 
Grounds and everything are good, went through and replaced all the wiring today. New spark plugs, J6c. Tested the spark plugs...getting good spark, compression test.... Both cylinders are at 118. Ran it on land, sounds like its running better. But ill have to take it in the water to tell for sure
 
The wires coming from the battery and the kill switch were pretty badly ran and frayed. So like I said I replaced them, but how would those affect how it runs if the coil under the flywheel goes strait to the spark plugs??
 
Are you mixing gas and oil at 50:1 ??------Is the waterpump working properly.------Have you checked for water in the fuel ?
 
New tank, new hose, new fuel, using tc-w3 synthetic, at 50:1 ratio, water pump works and theres a constant flow of water, the spark plugs where bright blue and jumped the 1/4". We spun the shaft and watched the points open and close in sync with the armature plate. The points look brand new and are clean, no corrosion anywhere. The ground is good, like I stated I ran new wires replacing the old ones. Everything under the flywheel looks brand new even the coil. Also there isnt any wire touching anything it shouldnt be
 
Have you looked into things like the reed valves ?--------Have you looked into an issue with lower crankshaft seal ?-----Plugged or partially plugged exhaust ?------There are still a few thing to check on these magic 2 stroke engines.
 
Took the boat out today it ran incredible, little hesitation but not bad.... still haven't done timing and everything stated above but I'm sure after that she will run like a dream... Would running synthetic oil and standard fuel instead of premium make a difference in anything
 
Ok, so I took the boat out yesterday. It ran pretty good for about an hour or so, still hesitating a little. Then it just started acting terrible in Fwd, Reverse, and neutral. If it was the timing or a gear issue wouldn't it do it all the time, and if it was a gear thing it wouldn't do it in neutral??... This is just confusing the hell out of me because everything looks as it should......
 
heres a thought. Could it be the pump??.
again though... I took it out one day and it ran great, hesitated a little but full power,
Took it out again yesterday, ran great for an hour or two then just ran like crap, it wouldn't go full power or make that typically 2 stoke whine noise, and a heavy jolt or shake almost as if it missing and it does it even when its idling
 
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