low compression need help.

luisjg

Cadet
Joined
Jul 16, 2004
Messages
27
yamaha 30 hp , 1994 2 cylinder.<br /><br />the motor starts right away and has a lot of power .<br />only thing is that the motor was in storage<br />for a long time and when i checked the compression,,,<br />i was surprice that the lower cylinder reads<br />90 psi and the upper 70 psi...<br /><br />wow!! this is bad...in fact the motor doesnt have more than 100 hours of used.<br /><br />im thinking that the piston rings are stuck somehow because of the lenght in storage,<br /><br />PLEASE HELP...<br />what do i do? <br />do you thing it will come back to normal after using it for a while or<br />should i be very concern about this.<br />or this is normal???<br />im preety dissapointed.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: low compression need help.

Hi, Luis.<br /><br />Tell us exactly what you did before and during the compression test. I suspect the preparation or technique produced your low readings.<br /><br />Was the engine warmed up? Did you have both spark plugs out? Was the throttle wide open? Was the battery fully charged? How many revs did you take on each measurement? Did you use a screw-in guage or a push in guage?
 

luisjg

Cadet
Joined
Jul 16, 2004
Messages
27
Re: low compression need help.

the motor was not warm, actualy i didnt ran in for 4 days before the test.<br /><br />no gas tank was conected.<br /><br />no throttle at all<br /><br />i removed one spark plug to do the test on the other then instaled the spark plug then removed the other and test.<br /><br />its a screw in tester<br /><br />dont know what you mean aboout revs.<br /><br />dont know about the batery beeing fully charged.<br />idont think so.<br /><br />should i do another test??? how should i do it.<br />this is the first time i d o it.<br /><br />THANKS JB!
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: low compression need help.

hello<br /> start the engine. allow it to warm up 5 min or so. remove both plugs, using a known fully charged battery and pull the stop switch lanyard, test each cyl through about 5 compression cyles with the throttles opened. in other words lift up the warm up lever. if its a pull start tiller then pull through about 5 compression cycles with the tiller throttle advanced. this is why we always ask for a model number. gives some of us a chance to figgure out what you have :) .
 

luisjg

Cadet
Joined
Jul 16, 2004
Messages
27
Re: low compression need help.

sorry about that.<br /><br />electric start<br />model c30elrs<br /><br />i will try that
 

luisjg

Cadet
Joined
Jul 16, 2004
Messages
27
Re: low compression need help.

OK <br />i did it again as recommended and i got the same result.<br />lower 70 <br />upper 100<br /><br />were do i go from here?
 

luisjg

Cadet
Joined
Jul 16, 2004
Messages
27
Re: low compression need help.

other waty arround sorry..<br />lower 100<br />upper 70
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: low compression need help.

I think a decarbonizing is your next step, Luis. Then check it again. That much difference could simply be carbon-fouled rings.<br /><br />Good luck. :)
 

luisjg

Cadet
Joined
Jul 16, 2004
Messages
27
Re: low compression need help.

thanks JB.<br />i will buy some yamaha ring free and give it a chok treatment.<br />if there is a way to decarbonize other than this please let me know.<br /><br />also<br />is it possible to open to clean the rings or im just getting ahead of myself here.
 

bigbrownbuku

Master Chief Petty Officer
Joined
Sep 17, 2004
Messages
885
Re: low compression need help.

its a complete tear down to physically see the rings luis. an engine stored that long may have impellor damage. was it pumping water from the telltale? merc powertune is product i use in the spark plug hole over night sometimes to try and help free up stuck rings. once started after this you will see a lot of black in the exhaust washed by the powertune from the trunk section. you should also check your thermostat, its quite possible it could be stuck closed, especially in a salt water engine.
 

luisjg

Cadet
Joined
Jul 16, 2004
Messages
27
Re: low compression need help.

yeah it pumps water fine , i just got a new water pump for it anyways.<br /><br />i will try to do the decarb deal,, i realy hope it works,,because new engines are preety expensive.<br /><br />its a shame though.. this engine looks in tops new condition im sure that it was used only ocacionaly.
 
Top