Compression question....

[60LOWRIDER]

My 1984 evinrude 40 hp has approx.100-105 psi in the top cylinder and approx. 80-85 psi in the lower cylinder. Although not optimal,should this be enough to run ? It starts and runs , but seems to be running on one cylinder. Both cylinders are getting spark and when i spray carb cleaner in the lower cylinder carb it surges.....

 

[F_R]

My advice is don't be messing around trying to make it "run". I say find out why the compression is low before it totally destructs. Could be a broken or stuck rings, a blown head gasket, or water getting in. Or a plugged carburetor causing that cylinder to run with little or no oil. Any of the above will lead to disaster.

 

[racerone]

Compression testers are certainly not all the same.----Tested a 2 cylinder last week with 150 on # 1 and 120 on # 2.-----It sounds like you need to clean the carburetors here.

 

[60LOWRIDER]

Has overheating issues that i 'm working on .ran salt away through it and the telltale works.the thermostat was clogged with pasty white so I vleaned it all out.Thats what probably caused the lower cylinder to run hot and lose compression. I cleaned the carbsthat reallywere not that bad.

 

[bonz_d]

try another gage if still the same results I'd say that engine is weak.

 

[Chinewalker]

Regardless of whether the gauge is accurate or not, if it is consistent, then you have a problem with the motor. I would not continue to run it until that problem is dealt with...

 

[60LOWRIDER]

I agree as it won't run full throttle at the moment. Ipicked this motor up over the winter as its the same model and only around 100 units off from my old motor and appeared to be in better condition.I swapped it out and started it with muffs but no telltale,removed lower unit and checked the pump,looked good reinstalled.Removed thermostat housing shearing 3 bolts,cleaned and checked thermostat and replaced after cleaning all that pasty white crap out.May have reinstalled pressure relief valve backwards.......Drilled out sheared bolts and installed Helicoils and reassembled.telltale now shows pissing ,but temp alarm still going off.Took out yesterday to see if ran different in real conditions.Bought home ran in container of salt away for an hour and checked compression.Water passages may be fouled with white crud still causing to overheat.When ran on water would not come up full power.

 

[SparkieBoat]

clean your carbs and if you overheated the motor you could try smoothing your head and a new head gasket. then maybe a decarb. you can clean out the water passages while the head is off. you should flush your motor every time you take it into salt water. you dropped your lower and looked at your water pump impeller and did not replace it with a new one? that is kinda crazy. Also you should use a good marine anti sieze on all of your bolts especially your lower unit bolts and head bolts. you found out why when you had to do all that drilling.

 

[60LOWRIDER]

Water pump assembly looked fairly new.....Used neversieze on everthing.Any thoughts on PRV? ,can't find any diagrams showing proper installation.... Replaced with longer end in spring and flat against the grommet with notch up...Might swap a carb off other motor to see if anything changes.....I might try to start my old motor on the stand to see what my compression is on that...its ran fine for the last 20 years though...

 

[bonz_d]

I've got a 1983 60hp, 1987 50hp and just sold a 1975 50hp. All 3 of those engines were running between 145 to 150lbs. So if there's nothing wrong with the gage then I would say you have a serious problem.