60 lbs compression 2005 25hp yamaha pls help

[Zjb187]

I have a 05 4 stroke yam 25hp it wasnt idleing good and found out it has 60lbs each cylinder.. used a clearer to clear out carbon buildup brought compression to 100lbs each.. next day only had 50 each... no scoring or anything on cylinder walls and rings dont seem to be stuck.. valve is working.. head gasket seems to be ok but i am replacing just incase.. what else could it be if not head gasket? what am i looking at paying here? thanks for any help..

 

[JB]

Re: 60 lbs compression 2005 25hp yamaha pls help

With both cylinders doing the same thing and delivering the same psi I would suspect testing equipment or technique before the engine.

 

[robert graham]

Re: 60 lbs compression 2005 25hp yamaha pls help

Rough idle probably dirty carbs or fuel delivery issue. You may be barking up the wrong tree on the carbon, compression as the problem. Check your entire fuel system from tank through carbs. Good Luck and let us know what you find!

 

[clanton]

Re: 60 lbs compression 2005 25hp yamaha pls help

Did you check the valve adjustment, may be too tight.

 

[Zjb187]

Re: 60 lbs compression 2005 25hp yamaha pls help

The compression test was done professionaly several times.. he cleaned the carb so problem shouldnt be there also prior to that i pumped out all of the gas and got fresh stuff even know the other wasnt bad so its not bad fuel.. and would the valve being too tight cause low compression??? anyway im sure the mechanic would know to check that.. i would hope anyways.. im just trying to see if anyone knows what this might be if not the head gasket.. he suspects the compression is leaking between the two cylinders causing each to have similar but low compression make any sence?

 

[Ruggybuggy]

Re: 60 lbs compression 2005 25hp yamaha pls help

After he clean out the cylinders compression went to 100 psi then fell back to 50 psi the next day? If he solved a compression problem it would still be at 100 the next day. I would take it to another shop for a second opinion before you let him tear into it.

 

[rodbolt]

Re: 60 lbs compression 2005 25hp yamaha pls help

carefully look at the parts manual, quite a few of the small F motors have an automatic decompression device.
if yours has it a compression test is a teat on a boar hog.
ALWAYS use a leakdown test on a four stroke.
more accurate and faster than a compression test.