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1987 Johnson 48spl wonbt idle compression

T

tranquility

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"Hi all, I have gained much kn

"Hi all, I have gained much knowledge from reading this site and have a question. This motor will start when heavily fueled and seems to run fine at advanced or wide open throttle. It will not idle however. A compression check showed 60/65 upper/lower. This seems low. Would this be the reason this motor doesn't idle?? The carbs have been gone thru several times and are spotless. I even removed all the plugs to check the idle passages and ran copper wire thru the siphone tube for the idle circuit. What effect does low compression have???"
 
"Thanks for the reply. I thou

"Thanks for the reply. I thought the compression was low, but the motor ran well at anything above real fast idle. It had power to push the boat fully loaded. I took your advice and pulled the cylinder head. The head gasket was in good shape with no deterioration around the edges or signs of blowby. The thermostat was corroded beyond recognition, but the cooling jacket was fairly clean. The cylinder walls were another story. They were moderately scored over 75% of the way around the circumference. Things came apart fairly easily without much corrosion, but I doubt I want to spend the effort to repair this thing since I can find a replacement for about the same cost of repairs.

My original question still remains. Does the low compression of the engine at idle cause the stalling and is the low compression compensated for as the engine runs at a higher speed? Opinions??

Brian Campbell
S/V Tranquility"
 
"at low idle,u r getting '

"at low idle,u r getting 'blowby',prob causing your idle prob's...at higher spd,it is just a faster result,i would say it is def overhaul time....esp due to low comp,and moderate scoring.u will never get it to run properly,w/low compression."
 
When a 2 stroke or any motor r

When a 2 stroke or any motor runs at higher speeds there is less time for air to leak.It is easy to judge the condition of a motor by the way it idles.The motor stalls because it is not making " power " due to it's poor condition.
 
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