86 Mariner 25hp not much speed

[neil271978]

The motor is running at about half the speed it is capable of going. I had a mechanic test it out in the water the other day. He ran some tests on it. First he bent the propeller back into normal position, he said it was bent pretty bad. That made it go a little faster. Also he said that the prop shaft was bent which could be causing it to lose speed. Also a month ago I took the boat out and it cut off on me and wouldn't start back up. I took it to the mechanic and he replaced the water pump and impeller and cleaned the carb. He said that the motor overheated. But anyway he said the other day when he took it out that the head gasket probably needed to be replaced because of the overheating. He tested the 2 spark plugs and one was normal (at 90 degrees) but the other one was black at 110 degrees. However he didn't seem too sure of himself about replacing the head gasket. Can anyone tell me if he is right or if something else is causing the problem.

 

[Deep_Blue]

Re: 86 Mariner 25hp not much speed

Check that your carburetor is adjusted correctly. And run a compression check.

 

[ozziebob]

Re: 86 Mariner 25hp not much speed

Find out where the head gasket is then find yourself another mechanic???????? Sorry for being stupid but I pull my hair out sometime with what I hear. Maybe this is a reare 25hp merc that actualy has a head gasket but I can count on one hand the one's that i have seen that does.(I dont know if these were made like this from the factory or are a modification for racing? but just about all have no removable head. Check your serial no and get on a sight to see a parts brake down as I think it will suprise you and will explain why your mechanic was unsure how to remove the head.......simply put you probably cant