Seca 400 Different Main jet sizes

[Jtoroli]

I was rebuilding the Carbs on my Seca 400 this saturday. Everythign went together really well. I did however notice one weird thing. The factory manual calls out 117 main jet for one cylinder and 125 main for the other. Can't remember which was which. THis is a vertical twin and so unlike an aircooled ducati both cylinders received the same airflow. Typically I would runt he rear cylinder a little rich on my ducatis. The only think I can imagine is that the difference is to pass emissions or possibly limit top speed.

Can anyone shed light on the reasoning behind the different Seca main jet sizes?

Best,

Joe

 

[bcware]

I believe it simply has to do with a quirky air box on that model of bike. It's normal. The threads below will tell you which side needs which jet.

Some other threads:

http://www.xs400.com/forum/showthread.php?t=6647

http://www.xs400.com/forum/showthread.php?t=10450

 

[Jtoroli]

Hi Bcware,

Thanks for the reply. Curious though. The intake runner is symetrical after the filter element. Difficult how to see there is anything in the airbox flow that would have this type of influence. I have left it stock for now which is fine. But my curiousity is piqued. I'll keep digging aroud for more information. Thanks again!

Joe