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1965 Johnson 3 hp low rpm

M

MarkVenema

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"I have been thru this motor a

"I have been thru this motor and replaced points, plugs, coils, spark plug wires, carb kit, etc.. and the motor still does not reach the RPM's it should. I tried choking a little to see if it is too lean. No change. Then tried turning off the fuel petcock to see if it is running too rich (would cause motor to rev right before it runs out of fuel). No change. I then replaced the float in the carb (also replaced the "boss" gasket again) and the head gasket. When replacing the head gasket, I noticed the bottom cylinder piston had hardly any carbon on it and was very clean where the top cylinder had some carbon and looked normal. I thought possibly this was a result of water from a blown head gasket or ??? was causing this condition. Could it be reed valves or poor rings? I have done done an actual compression check but it seems very good when pulling the rope. Any suggestions? or where I may find piston rings/gaskets for this motor? I could not locate those items on this site. Thanks, Mark."
 
"If you are getting good compr

"If you are getting good compression then you probably don't need new rings. But if you have a local marine shop they should have them, if you absolutely need to replace them."
 
"Mark,
On the small engin

"Mark,
On the small engines it is difficult to even guess at compression based on the pulling the starter rope. A compression gauge is dirt cheap at any auto supply shop. Buy one, pull the plugs and find out. Note, you should add a squirt of oil to each cylinder and crank it a few times to get an accurate compression number. 80 psi is acceptable, 90 is pretty good and above 90 is excellent."
 
"Okay, I checked compression d

"Okay, I checked compression dry and it was 60# in each cylinder. With oil, it went up to 70# each cylinder. The bottom plug appeared to be damp looking compared to the top cylinder plug. I then visually checked spark and they both looked the same. Why would that cylinder appear "wet looking" compared to the top cylinder? I don't know anything about reed valves...if they were bad, would it affect both cylinders? Maybe it is a weak coil, plug or condenser or faulty points, but the spark looks the same on both?? Any ideas? I know 70 PSI is not the greatest, but they are both equal anyway. Thanks for the responses! Mark"
 
Is it running on both cylinder

Is it running on both cylinders??? Disconnect one wire at a time and see if both cylinders are firing.
 
"I am out of town for a week,

"I am out of town for a week, so when I get back, I will disconnect one wire at a time to see if that is the problem. With one cylinder plug looking different (i.e wet and nearly zero carbon on the piston and head), it leads me to think something is wrong there. But yet I have the same compression and same looking spark when pulled over by hand. I even set the points with an ohm meter to verify timing was exact. Can it be the reeds? Maybe something is happening with the coil/condenser/points at higher speed? It seems to be okay at slower speed, but maybe it is just one cylinder firing for some reason....thanks for the suggestion. Mark"
 
Test the spark by using a 1/4&

Test the spark by using a 1/4" gap or bigger. Guessing at spark by laying a plug on the block is a waste of time.
 
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