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1999 yamaha 50hp deto model

W

weejohn

Member
just bought a 50 hp from a guy i was told the psi was 120 got it delivered today . the engine looks new just had a full respray and a very good job it is . the engine starts first turn of the key . i done a compression test and all 3 cylinders are 90 psi , i phoned the guy to my surprise no answer . do i do a compression test when engine is cold or warm ? also is 90 psi ok to run , i know i will loose a little top end power but apart from that will it be ok .
 
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A compression check should be done with the engine fully warmed up. Battery should be fully charged and the throttles wide open. Crank until the pressure stops rising.

90 PSI is not abnormal. It is well above the minimum specification for that motor.
 
boscoe many thanks for your advice . i will do a compression check tomorrow the way you said . i done it from cold and never done the throttle wide open i will let you know the psi if there is any difference . cheers
 
done another compression test as was advised to do by heating the engine and opening the carb full open . no 1 cylinder 1100 no 2 cylinder 1115 no3 cylinder 1100 is this ok ?
 
The number look fine. Better than they were before, right?

Some say it does not matter with a two stroke if the motor is hot/cold or throttle opened/closed. I think you have found out that it does.
 
cheers i also noticed when using the compression tester with the screw bottom and ring seal it gives a false reading i used the cone bottom and held it in with my hand while turning it over . i took your advice with carb open and carb closed like you said it was better full open . ;)
 
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