Compression sws 150's 1994

[130mckee]

I have an even 100psi in all six cylinders on both motors. Is this normal
And if I decarb motor should these numbers rise alittle? I thought 100 to be normal but some say it's kind of low. Motors run like raped apes so I think those compression numbers are good. Motors have 990 & 992 hours and hope to have for another couple thousand hours. Any help would be great!!!!!

[jb123]

those numbers are ok,even is what counts
tell your friends they ARE 18 yrs old.....
decarb could help

[130mckee]

They sat without being run in a year still winterized. Have to clean them up for this next fishing season. Have to get a shop manual.

[robert graham]

Maybe run a tank of gas with "deposit removal" dosage of Seafoam or Ringfree to remove whatever carbon may be on the piston rings or in their grooves. I run the Ringfree all the time at the "deposit prevention" dosage, good preventive maintenance and a Whole Lot cheaper than stuck rings! Good Luck!

[130mckee]

Was wondering what should be done before they are run. I don't want to damage them. I've never let my boat sit so long so preventative maintanence or what has to be gone over to save on damage. These are my babies and I don't want to hurt them. To expnsive to replace.

[99yam40]

Drain and clean the fuel system to get rid of all of that old fuel

[TownsendsFJR1300]

Motor

If you squirt a little Seafoam in each cylinder before cranking will help lubricate things on initial turnover..

If you can find a small syringe, put a small piece of hose on the end of it and you can get it to about any opening(spark plug hole)..

+1 on running the Seafoam in the tank. You can run it on the heavy side as it won't hurt anything and will help stabilize the fuel...

Also +1 on draining the carbs.
Pull the drain plugs (one carb at a time) and put a small tuna fish can (clean) under the opening and drain. Squeeze the primer several times (while the drain plug is out) and get fresh fuel in the system. Look for any debris/water coming out of the bowls.. Repeat for all the carbs....

[130mckee]

Fuel tanks are empty carbs are getting cleaned by me next month but my concern is more the oil that spent a year in the remote tanks. Fuel doesn't scare me it's more the oiling system from sitting. I have never serviced the oil side of the motors. I have rebuilt yamaha carbs a bunch of times.

[robert graham]

Fuel tanks are empty carbs are getting cleaned by me next month but my concern is more the oil that spent a year in the remote tanks. Fuel doesn't scare me it's more the oiling system from sitting. I have never serviced the oil side of the motors. I have rebuilt yamaha carbs a bunch of times.

The oil don't degrade like fuel, but if you're worried about your oiling system not working right, run a 100:1 gas/oil mix in your first tank just to be sure until you determine your oiling system is working right...cheap/easy insurance!

[130mckee]

Will have to bring a few portable tanks out on test run this year. Going to change both head gaskets on both motors. Also gonna shock it with seafoam after I clean the carbs and change head gaskets. New water pumps and fuel pumps. Almost forgot spark plugs and Gear oil. Boat is new to me just want to make sure I cover all bases to keep these motors running. Like said sat for a year and I finally convinced owner to sell because he was no longer able to use. Definatly not my first yamaha so I am familiar with carbs and rebuilding them.