Yamaha 225 Compression problems?

[cjb225]

I have an 89 Yamaha Excel 225 that has lost rpm's and power. The motor starts fine, idles fine, and bogs down getting on plane. RPM's max. at 4400 - 4500 and top speed is about 12 mph below normal. I changed the fuel water separator, primer ball, helped some but motor still surges lower rpm's and overall speed. Checked compression with the left top and bottom cylinders at 110lbs, middle 130lbs; right top and bottom at 120lbs, middle 130lbs. I changed the plugs but have not run boat since. Should I be worried about compression differences? What should I look at next?

 

[edgutgesell]

Re: Yamaha 225 Compression problems?

CJB,

Have you tried to decarb the engine? The compression difference from 110 to 130 seems to be more than normal and may be corrected by decarbing. Do a search on "decarb" and you will find out how a decarb is done.

 

[rodbolt]

Re: Yamaha 225 Compression problems?

can ya post it per cyl? your description is frying my brain.
quite a lot of yamaha motors have built in differences in compression, measure them bank top bankie 1-2,4-3,5-6. that way the 10 psi rule works.
a better test would be a leakdown after a decarb, if the leak down is within 15% then a good fuel system tune up will be in order most likly. carbs and fuel pumps dont last forever and need periodic service.

 

[cjb225]

Re: Yamaha 225 Compression problems?

Thanks just ran decarb through motor, a thunderstorm came up and wasnt' able to test it. I had the carbs rebuilt approx. 100hrs ago, motor has 870hrs. Sorry about frying your brain rodbolt, I will repost with new compression and leakdown the way you suggested. I will check fuel pumps when the weather allow's, we are into our summer weather pattern with afternoon showers every day. Thanks for your help

 

[Ray Neudecker]

Re: Yamaha 225 Compression problems?

That model was one where the compression would drop from the top bank to the bottom by about ten pounds.