Topic: Overcross - why?

[efair]

I've become the caretaker of a family relic CB750K1, I had to remove and clean the carbs due to frozen piston valves.  I've been reviewing the shop manual with an eye towards the initial settings and the final tuning and I'm wondering what the purpose of "overcross" is.  Looking at the mechanical components and how I think they work: simply releasing the throttle grip allows the pistons to snap "mostly closed" to the idle position; twisting the throttle even further towards the slow allows the pistons to close even further.  What is the purpose of this?  Is it simply to allow engine braking?

[Don R]

 I believe it is to assure closure of a hanging slide.

[Bodi]

I think you're wondering about the dual cable throttle, I haven't heard "overcross" before.
This is purely a safety design. If the carb rack mechanism jams open, the rider is probably in trouble. It's a lot of mechanism. The return spring is pretty strong and they could just put in a really heavy spring but throttle effort would be ridiculous.
So the spring generally works great, but if something like gummed up slides sticking happens you just twist the throttle forward and force the slides down.

[newday777]

I've never heard of "overcross" before. Where did you get that from efair?

[TwoTired]

I always thought the overtravel springs were to relive stress on the close cable from overzealous throttle shut down efforts, and to keep all differential play out of the actuators.

Cheers,

[jaytee-nz]

"Overcross" is referred to on page 195 of the K1-K8 workshop manual supplement (in the manuals section of this site).
Doesn't really explain what it's for though, just how to make adjustments.

[efair]

So two votes for "safety mechanism" and one vote for "end play adjustment".  My vote is "engine braking".  Thanks for all your replies, and correct: overcross is mentioned in the shop manual but is not described.  Unfortunately the operation of the two cables below the throttle grip isn't even mentioned.

Can anybody describe how the dual cables in the throttle grip work exactly?  Or post photos?

I'm 1000 miles from the bike for a few months, so I can't just look at it myself.

[ofreen]

The owner's manual for my '75 F calls it the "overriding stroke."  I've always used it to cut the revs a bit when shifting into first from neutral.  It does ease the mechanical clashing a little.

[efair]

Thanks, that's helpful.  The (somewhat fuzzy) 750 shop manual does appear to show three distinct arcs of travel, as does yours; the middle arc being what I would normally call end play.  I do wonder where your measurement, 1/8" to 1/4", would be taken though.

[ofreen]

I do wonder where your measurement, 1/8" to 1/4", would be taken though.

Looking at how mine works, that 1/8 to 1/4 would be measured at the outer circumference of the grip as it moves through the arc.

[efair]

Got back on it today - the second throttle cable is totally missing from the bike.  The good news is the carbs are back on.