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Stepper Motor - an observation

T

tris

Cruisin' Guzzisti
Joined
May 30, 2012
Messages
256
Location
Lincolnshire UK
I suspected that at the stepper on my B11 was "less than perfect" - it was graunching and the like

SO I bought a stepper controller on line so I could stroke it back and forth on the bench and cleaned it with an inch of its life which was fine

However, I found that if I closed the valve completely and gently blew through the inlet one outlet passed air and the other didn't. Not a colossal amount but definitely leaked

Then I bought a secondhand one of a Ducati (£21 as opposed to £300 ;)) for a spare and it does exactly the same thing

So I guess my question is do they all do this?

My thoughts being that it should only be open at idle I believe, and does it have this asymetric flow at idle as well thus needing the air bleed screws open to even things out

Any thoughts team??
 
My thoughts are just like yours. Asymmetric flow as you have observed w/tester, although I have not tested one on the bench like you. This is why one air bleed screw is open just a little.
 
And yes, they flow air when "closed." Part of the silly design (flaw IMO).
 
But that they flow air, even when closed, is why you can get an improvement by turning the system off. A valve capable of turning the system off seems to improve throttle decel, when you close the throttle with the system off / out of the loop the engine displays a more immediate decel. I like that, for me it makes shifting and general riding more as I prefer / expect.
As long ago discussed, mine has a valve that allows me to turn the system on for cold starts and turn it off once warm enough that it does not need the system to idle.
 
Thanks Todd - I'm glad its not just me that found that they leak!

Can we expand this leak theorising a little further

We know that at idle the SM is open some amount and the TBs are closed and as the TB opens at some point the the SM is fully closed

Is it a reasonable hypothesis to assume that at some small TB opening with the additional leak past the SM the engine is receiving more air than the ECU thinks it is giving rise to lean surge?

Do you people that have fitted a valve suffer lean surge when cruising at low throttle positions?

If the hypothesis is correct then you shouldn't
 
I don't think the ECU knows how much air the stepper receives. I do know if you put a shut off valve in the feed air hose from airbox and shut it off it idles normally. That is because it gets air from the air bleed screw that is slightly open.
All the problems w/metal steppers is why Guzzi put the later plastic stepper on their bikes.
Many riders put the valve in the airbox hose to vary the rpm till engine is warmed up fully then shut it off manually.
 
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