Yamaha Seca 750, 1982 model

[Bonz]

There was a Yamaha tool you inserted into the YICS port that had a lever to expand rubber on rod to block the ports when syncing, don't know how much difference it made.

I believe it makes a difference. Sync'd w/o tool, thought it was good based on gauges. Looking back, they would be easy to line up sharing the same vacuum in the YICS port as has been said many times.

Used the tool, that showed they weren't good if having all 4 lined up is the goal. $68 front ebay, original Yamaha tool, shipped from Japan. Took a while but worth it.