Compression testing

[SPEEDSTER95]

Hey Guys

I have been reading on the site all about testing compression and it should be 120 with min 10% between cylinders.
Now please excuse me for sounding ignorant, but 120 what? I know you guys work in imperial, so I presume this is 120psi.
The reason I ask, is because 1 of my engines ( port side ) is giving me extreme nightmares. Battles to start and when given gas , it dies!
I have removed and re-done the carbs , ie new gaskets, pump gasket was stretched, new needle and seat etc. All set up according to the manual.
I have not tried it yet but was also thinking of checking the compression. The bloke I bought it from told me the engines have recently been overhauled.Being a mechanical engineer, I am a natural sceptic, unless I have done the work myself. I have also replaced all the fuel and oil lines. I have also isolated the oil pumps as being fairly old ( 1995 ) I dont trust them.
Anything else I should check??

 

[Moto-Madness]

120psi. You can buy a Compression Guage at your local automotive store for about $25. Remove the spark plus wires and remove one spark plug. Screw in the Compression guage fitting and crank the engine over about 4-5 revolutions which will give you a pretty good reading.

 

[SPEEDSTER95]

Thanks for the speedy reply. Got a gauge, will try tomorrow night. Too bloody hot here during the day,46 deg c plus today was about 80% humidity!! Was just trying to confirm about the psi or kpa measurement. ( have to say, I figured it had to be Psi as 120 kpa is WAY too low)

 

[Moto-Madness]

I also removed the fuel line to the carbs so I didn't flood the engine while doing it.

 

[cjb]

You should do the test at wide-open throttle. Just crank the engines with the throttle open untill the needle on the gauge stops moving. Also dont forget to ground the spark plug cables.

Isnt compression supposed to be at 150psi?

 

[seadoo GTS 1993]

150 is ideal, down to 120 is acceptable

 

[SPEEDSTER95]

OK. Have to admit, never thought of disconnecting the fuel line:redface:So between 150 and 120 is OK ?did click about grounding the plugs though!

 

[seadoo GTS 1993]

Rite, If compression is 120-150 then u got a strong motor