4 Attachment(s)
Why 100% Matters in a Time 90% is Accepted
I've had 3 cylinder 2 stroke Yamaha outboards since 1990. They have a particular idle when everything is right and a very detectable miss when it is not. Old Crossflow OMC engines had this issue too when you do everything right to tune it but the lean idle miss or sneeze kinda hangs around. Another principle I live by is "A lazy man does the most work" and this one bit me by not following through. So I'm breaking in the built Powerhead and can hear it still isn't right, the extra shake to the Cowling, the 3 cylinder hit followed by only 2 cylinder hit at idle, kinda weak off idle to butterfly opening when the throttle is ramped up. This can not be tuned out with Carburetor adjusting because the cause is not there. It is not electrical either. I trusted my bud to do 100% work on the Powerhead but he is young, very good at building powerful powerheads for Drag Racing but the 100% follow through isn't there. I should have check behind him but there are lots going on here besides this project so I put it together without my usual 100% nature in practice.
Attachment 514588
Behold why I had to pull the Powerhead back off. The silver fitting you see right over the 2x4 centered in the bottom of the Powerhead is a Check Valve. This Check Valve drains excess oil off #3 cylinder and during the cylinder's Pulse pushes the oil thru the Check Valve towards the Upper Crankshaft Bearing which my Bud had to replace with no less than 15 hours on the new one. I didn't check this Check Valve when I initially rebuilt this engine, I didn't check it while the powerhead was off, I didn't check it before reinstalling the powerhead, see where I'm going here. So the Check Valve is stuck open, the top crank bearing is not getting oiled properly as the oil is just moving back and forth in the hose. Well fuel/oil mixture is also pooling in the bottom cylinder causing excess enrichment of the mixture creating the miss.
Attachment 514589
The 2 Check Valves in cylinders 1 & 2 are fine. These Check Valves oil other Crankshaft Bearings.
Attachment 514590
I'm not sure where this Check Valve is draining excess oil but it also feeds the top Crank Bearing. The top bearing has 2 oil lines on a Yamaha 3 Cyl 2 Stroke. This Check Valve is a different part number than the other three also. Well this one is stuck open too. OMC engines have these Check Valves too and when they are stuck open you can't tune them to idle right until you replace the check valves.
To check for proper Check Valve function you load a syringe with alcohol and attach the syringe to the hose going to the Check Valve. You should NOT be able to push alcohol thru the valve but you Should be able to suck air back thru it. I Should have done that before installing the Powerhead but didn't. My Bud said it was a waste of time. Well all 2 stroke outboards that oil the Crankshaft Bearings this way using check valves can't be tuned to idle smooth as fuel/oil mixture pools in the intake passageways.
Back to why I had to pull the Powerhead.
Attachment 514588
This fitting is Pressed In not threaded. I had no way to replace the fitting while the Powerhead was installed. A lazy man does the most work. Since this is a 1999 Block I ordered all new replacements. Once back together and running I will follow up here.
Attachment 514591
Perfection has a price.
