Yamaha 60 - Down on Power

[Paul_Dublin]

Have a pair pr Yam 60's (1996).<br />Both run and start well. Both identical props.<br />Left motor down on power, so did rebuild with OS pistons. Got compression up to 125/125/110 but it's still not getting as much power as the other motor.<br />"Good" motor will get over 5700RPM (will always back off to 5500)<br />The weak motor will struggle to get more than 5200.<br />I've tried swopping the complete carbs but this makes no difference.<br />The fuel pump seems to be pumping well when tested and no visable restrictions on the fuel lines.<br /><br />Is it possibly the timing?<br />As the other motor is identical, is there anything I should swop as a test?<br /><br />Any other suggestions?

 

[ivar]

Re: Yamaha 60 - Down on Power

You have tried swapping the props too?

 

[Paul_Dublin]

Re: Yamaha 60 - Down on Power

Yes, I changed the props after the rebuild<br />Both were brand new.<br />It just seems to be down on power.

 

[jim dozier]

Re: Yamaha 60 - Down on Power

How do the spark plugs compare from the good engine to the weak one. They can often give you an indication of a bad cylinder or a lean condition. If the compression is good it has to be fuel, timing, temperature (overheat), friction (such as lower unit problem), or prop. Get a manual, check the timing on both engines, and get a point and shoot laser thermometer and check the temperature in several places on both engines.

 

[Paul_Dublin]

Re: Yamaha 60 - Down on Power

Sparks are good (bit wet, but not too much)<br />Compression is 15PSI less on bottom Cyl, but I think still in Specs.<br />I would think Fuel is OK as I have completely swopped Carbs from sister motor.<br /><br />I've dropped the lower unit, and it seems pretty smooth.<br />Just put new props on.<br />That just leaves the timing and temp. <br />I think the cooling should be ok as it's flowing pretty good and I can still touch the motor without burning myself. Is this a reliable way?<br /><br />I have a manual, but the timing is the only thing I'm not too clear on.<br />I can get a dial guage and check the relationship between Flywheel and piston at TCD.<br />Can't get a strobe light to check without having to buy one though.