Need help: YS828 intake valve not fully closed on compression stroke
Hello, I have a weird issue with a YS828 engine...
It is very difficult to start. When running I remarked that the carb was spitting out some fuel during acceleration.
Did the following tests:
1- Took a compression reading, got 78 psi.
2- Put my hand over the carb inlet during cranking and felt succion and then some pressure (which doesn't look normal)
Suspected bad valve timing or misadjusted intake valve, so I removed the cylinder head to look at valve opening sequence and everything is fine. I checked the valve gap at TDC and they are both at 0.006 (specs is 0.005 to 0.007) = OK
Then I cranked slowly the engine and found that the intake valve doesn't fully close during most of the compression stroke (I can rotate easily the valve with a finger). The valve close fully only when the piston is at about 0.5 inches before TDC... This might explain the hard to start and spitting.
My question is:
Is it normal ? Is it a trick that the Yamaha engineers took to reduce the compression for an easier cranking ? This is not mentioned in the shop manual.
Note: This engine camshaft has no compression release system, and usually those systems are partially opening the exhaust valve during the compression stroke, not the intake valve ...
Does someone have a spare parts engine they could use to validate this ?
I'm stuck, I don't want to grind the intake valve stem to allow the valve to close fully during compression stroke, I will end up with a valve gap of 0.016 at TDC and during all the explosion and exhaust stroke...
Thanks for any help