low compression in one cylinder

[eveningtide]

took compression test all holes have 120 but left bank in the middle has 50 this is a 1998 1200 hrs yamaha 200 salt water with carbs what should i do now

[robert graham]

You may have carbon stuck piston rings on that piston and/or grooves in that cylinder wall. A shop could put a scope into the spark plug hole to inspect cylinder wall for grooves. There's a chance you could do a decarb on your motor to try and free up the stuck rings, then check your compression again. If it's still low then you'll be looking at some expensive repairs on that motor. Good Luck!

[eveningtide]

thanks that is what i am going to do got a bore scope from a buddy if all looks good than what is the best way to decarben rings

[robert graham]

Yamaha has a product called Ringfree which you can mix in a tank of gas and run through your motor, possibly free up rings. Some folks also use Seafoam, and a few other Carbon Deposit removers. After you run about 10 or 15 gallons of gas through your motor(while running the boat), check spark plugs for possible fouling caused by decarbon process. Ringfree is about $40/quart, and decarb dosage is 2 ounces per gallon. Good Luck and keep us posted with results!

[eveningtide]

well its not carbon looked inside with scope and not good. poped the head off for sure not good. looking to pull power head and bring home to see what can be done. thinking of clean up the bore, go from there.

[robert graham]

well its not carbon looked inside with scope and not good. poped the head off for sure not good. looking to pull power head and bring home to see what can be done. thinking of clean up the bore, go from there.

Not so good!...If grooves are not too deep then cylinder may be honed or bored oversized and an oversized piston and rings installed. Maybe stuck and/or broken rings have scored cylinder walls. The Ringfree Additive is recommended at a "deposit prevention" dosage of about an ounce per 10 gallons of gas to help prevent carbon on rings and in ring grooves. While you're in there for repairs check other pistons, rings and cylinders for carbon. Good luck with your repairs!

[eveningtide]

well something got in the cylinder reed or a ring not sure, need to finish taking apart. so the cylinder is done need to sleeve or go with a short block. limted on time and cash, this is how i make money charter capt. so my ?? is which would be the fastest and cheepest way to go. i looked on line for out broad machine shop in jersey and cant find one to call about sleeving all i fine is one in PA. and FL. has alot. help what to do iam pulling my hair out and my season is just starting.

[boats.net]

Crank Cylinder Assemble(powerhead) is the quickest but not the cheapest, number one in this diagram is a new powerhead assemble, Make sure this is correct model number and make sure to oreder the part number for the 200 hp, 1998 S200TXRW Yamaha Outboard CYLINDER CRANKCASE 1 Diagram and Parts

[Tucker]

Believe you can buy these all day on ebay for around $3,000. Yea, a bit risky but if they offer a warranty and the motor has good compression, you should be able to fix anything from your parts motor.

[robert graham]

Since it's a 14 year old saltwater motor, maybe find a similar used motor and buy it. If same model and HP, just hook it up and go...keep your old motor for parts!...they could come in real handy after a while! Good Luck!