25hp Mariner problems

[BigDaddy300]

The motor bogs when at WOT. Came to the conclusion that it was starving for fuel. The ball was firm but while running at Wot I pumped it anyway. As long as I kept pumping the ball it would run great, but when I would stop pumping it would starve again and bog. I did this 2 times in a row for about 1minute. Then it started idling bad and stalled. It would start but would not idle. Then I had a hard time starting it. To make a long story short I got it back on the trailer and pulled the plugs bottom plug was good but the top one was wet with water. I was told that it is a blown head gasket. Could I have caused this. Can it be some sort of other problem?

So I am asking for advice on the fuel problem and the water in the cylinder problem. I was told the head gasket is not that difficult to replace. If this is the problem and I attempt this where can I get the torque specs and sequence? Thanks for any help.

 

[WillyBWright]

Re: 25hp Mariner problems

If it's a Mariner with a head gasket, then it's a Yamaha. The torquing value and order might be embossed right on the head. There will be numbers 1 thru 10 by each bolt, and the torq somewhere. Kinda like drawing by numbers. If it isn't Yamaha-made, then it doesn't have a head gasket.

 

[BigDaddy300]

Re: 25hp Mariner problems

It is made by Yamaha. It is a 1983 model. I will look for the numbers. Thanks

 

[BigDaddy300]

Re: 25hp Mariner problems

I took the head off and it was definately a blown gasket. What is the best way to prep the surfaces of the head and block for the new gasket? Is there anything else that I should do while the head is off? Anything that I should do to the top of the pistons? Also I did find the sequence and specs for torquing but it is in metric I think. Can't remember the measurement and I can't get to it now but I think it was 28 something. Any ideas what it would be in foot pounds or foot inches. Thanks for any help

 

[BigDaddy300]

Re: 25hp Mariner problems

Bump.

Anybody have any help to offer? Thanks.

 

[Scrottocks]

Re: 25hp Mariner problems

Big Daddy300,​

I have a manual for the Mariner (Yamaha) 20/25/30 models - from about 1977 onwards, so probably covers yours. Mine's a 20.​

The cylinder head final torque is given as 18 to 25 ft.lbs = 2.5 to 2.8 kg.cm. (cm is wrong, should be kg.m). Elsewhere in the manual the figure of 2.8 kg-m = 20lb.ft is given. The "2.8" might be the "28" you mention in your post. They also refer to applying Loctite 'A' to the bolt threads.​

Hope this helps,​

Scrottocks ​

 

[Scrottocks]

Re: 25hp Mariner problems

BigDaddy300,​

If you PM me your email address I will try to scan the pages of the manual re. the head/pistons/re-assembly, etc. and email them to you. ​

Scrottocks​