Cylinder 1 firing on intake stroke


CB750 New member
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Raleigh, NC
Hi all, I have an interesting issue.

I'm pretty new to bike building but I'm here to learn. I recently rebuilt my CB900C (very similar to the CB750) engine after a blown head gasket. I followed the manual to the T when rebuilding. I made sure the 1.4T index mark was lined up while the sprocket punch marks were horizontal etc.

However now while trying to start my engine (and troubleshooting with starter fluid because it's not starting well), I'm finding that cylinder 1 is firing on the intake stroke. If the choke is on while starting it it will blow the carburetor off the boot, and if the choke is open it will blow a little white smoke out of the carb air intake.

I have made sure my coil wires are connected correctly so I'm at a bit of a loss. Any advise on where to start looking or things to check would be much appreciated for a novice like me.

Thanks in advance!