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1985 50hp lost bottom cyl compression

mountman62

New member
my 1985 50hp lost compression on bottom cyl, has set up for over a year, craked it up and ran fine for around 10 minutes, then started missing, checked carbs, fire, all ok, check comp today, top cy 130 lbs, bottom cyl 75 lbs, would it maybe be the cyl head gasket or worse, head or cylinder rings, hoping not too bad
 
Very common on that motor.----Likely scored a piston and cylinder bore.----------Pull the cylinder head off to inspect.----Lucky you if it is just the head gasket.---------------If oil injection is still in use, then did you run with 50:1 mix in your tank untill VRO was confirmed to be working properly.---Was water pump impeller maintained / replaced ?
 
I'm having the same problem. 1984 Evinrude 50hp spins over good an will pop every now an then through exhaust, fresh 50:1 gas, rebuilt carbs, top compression 130 bottom 80, timing checked good, plenty of spark will arc over 1/2", no blowing back through carbs, also checked both cylinders with a bore scope they don't a peer to be scored up. I understand low compression on bottom cylinder is a problem but shouldn't it still try to run on upper cylinder an just have a bad miss. I even tried a shot of starter fluid that I hate because it's to hard on the motor but still no change made zero difference.
 
XRider, mine will run a little on the top one only, yep, it pops & blows like some black smoke back thru the exhaust, hope i can take the head cove & head off tomorrow and just find a bad head gasket, with the 75 or 80 lbs of comp on the lower cyl, i think that the rings would be good, otherwise the comp level would be a lot lower, just wishful thinking, but just maybe i will get lucky
 
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