Author Topic: Service code 62: Subthrottle valve actuator malfunction - how bad?  (Read 917 times)

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Offline TowerMan

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*Originally Posted by senpai71 [+]
So what does the subthrottle valve actually do? Does it simply improve things at low revs and/or cold engine?

Basically, if it stops working, does it really matter?

Due to emission and noise control regulations secondary throttle valves appeared in motorcycles in the last couple of decades.
The STV system does a couple jobs.

It's primary function when the engine, is running is to manage intake port velocity to keep the power curve smooth.
As RPMs increase or decrease, they will open and shut to perform this function.
This secondary butterfly is controlled by the bike’s ECU.
For maximum performance and crisp throttle response this secondary system can be removed – in drag racing / road racing.

The secondary function is to control the fast idle system.
On the opposite end of the secondary throttle shaft is the fast idle cam.
When the secondaries rotate open, the cam engages the follower to press against the high idle screw.
Basically, it just bumps the throttle open a little.

If it stops working and remains shut then you will have no power.

If they fail open then the bike will bogg down at low revs then come on song as the air intake velocity rises

Aslo see this link -
Last Edit: January 10, 2020, 11:42:22 AM by TowerMan
Richard    :001: