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JamesW

Clutch Switch

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JamesW

I am totally confused about how the clutch switch works on a BMW oilhead.  My bike is a '93 so the clutch switch is located in the clutch assembly.  My bike starts and runs the same with the switch connected or not.  What is the purpose of this switch.  The switch simply applies a ground to the starter relay when the clutch lever is pulled in and I can't see what this is supposed to do or how it does it.  So, I need enlightenment.  I'm probably out in left field here but I've been thinking that the clutch switch has something to do with engine cut off which occurs when you roll off the throttle while disengaging the clutch as occurs during an up shift.  I'm assuming the BMW has this engine shut down feature.  In studying the schematics of the engine circuit in the Haynes manual I can't understand what the  clutch switch is doing or how it does it.  

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Warren Dean

That is among the many design mysteries that plague Beemer riders.  Then add in if the neutral lamp is illuminated, no need to pull the clutch in...if it is off, pull the clutch in. But mine is intermittent so sometimes I have to pull in the clutch and sometimes I don't.  I just pull the clutch in every time and just ride.  :)

 

 

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szurszewski

I'm not sure if you're asking for the mechanics of the circuit path - which you would understand better than I - or what the purpose is. 

 

Assuming the '93 works the same as the later oilheads I have, it's purpose is to keep us from accidentally starting the bike when in gear without pulling the lever/disengaging the clutch. Electrically, does it not work the same as the sidestand switch? That was my assumption, but only an assumption.

 

 

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JamesW

I studied the wiring diagram some more and I think the switch works like this:  If the side stand is up and the transmission is in gear and the clutch is engaged then the bike won't start until the clutch is disengaged.  I don't see any way that the clutch switch can disable the engine when making a shift.  I think the Motronic is in charge of that function and that's assuming the early oilhead even has that function.  I went for a test ride with the clutch switch disconnected and I could have sworn the bike shifted smoother but it was probably just a kind of placebo effect and wishful thinking.  Not saying my bike shifts poorly at all.    I'm going to leave the clutch switch disconnected and whenever I go to start the bike in neutral or not I always disengage the clutch anyway.  Maybe I'm just bored.:P  

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Miguel!

Consider this  scenario... You stop at a light but forget to downshift from, say, 3rd or 4th. Light turns green and you stall the engine. You can pull the clutch in and  start the engine while in gear. Otherwise, you have to find neutral before starting, holding up traffic behind you.

 

Miguel

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JamesW

I do wish there was a way to eliminate fuel cut off which occurs when you roll off the throttle when making a gear shift.  If this fuel cut which shuts down the fuel injectors when you back off the throttle could be eliminated the result would be easier and smoother shifting without having to coordinate foot shifter, de-clutch, and throttle roll off all with such precision and co-ordination to attain that smooth gear change.

 

What got me started on this was I had my FJR ECU flashed by a well known tuner and the end results are nothing short of amazing.  One of the things he did was turn off the engine cut that occurs during shifting when the throttle is rolled off slightly as the clutch is disengaged.  No more lurching or clunking from the transmission at all and you don't have to be as quick and precise with the clutch, throttle, and shifter.  The reason for this engine cut is emission reduction since an engine that is not running does not pollute.  This is kind of ridiculous on a motorcycle, imo.  

 

I don't think there are any tuner guys out there that are doing this kind of work on BMW bikes at least none that I can find.  Actually my R1100 shifts pretty good as is but I think it could be better.  

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dirtrider
9 hours ago, JamesW said:

I do wish there was a way to eliminate fuel cut off which occurs when you roll off the throttle when making a gear shift.  If this fuel cut which shuts down the fuel injectors when you back off the throttle could be eliminated the result would be easier and smoother shifting without having to coordinate foot shifter, de-clutch, and throttle roll off all with such precision and co-ordination to attain that smooth gear change.

 

What got me started on this was I had my FJR ECU flashed by a well known tuner and the end results are nothing short of amazing.  One of the things he did was turn off the engine cut that occurs during shifting when the throttle is rolled off slightly as the clutch is disengaged.  No more lurching or clunking from the transmission at all and you don't have to be as quick and precise with the clutch, throttle, and shifter.  The reason for this engine cut is emission reduction since an engine that is not running does not pollute.  This is kind of ridiculous on a motorcycle, imo.  

 

I don't think there are any tuner guys out there that are doing this kind of work on BMW bikes at least none that I can find.  Actually my R1100 shifts pretty good as is but I think it could be better.  

 

Morning James

 

On your BMW you don't get fuel cut-off until a fully  closed throttle so just don't roll the throttle all the way off during the shift.

 

Or just ride with the choke on (actually fast idle only)  as that prevents the TPS from dropping low enough to enter dropped-throttle fuel cut off. It also prevents the engine RPM from dropping real low on the shift so you don't get all the engine-compression-braking during the shift.

 

If you turn off the fuel cut-off then you won't like the popping & farting in the exhaust system on decel as you will have fuel injected with very little air entering to allow it to burn off that fuel. 

 

A lot of your shifting problem is that you are riding a somewhat large piston 2 cylinder boxer engine motorcycle. That engine configuration has a LOT of dropped throttle engine braking. If you are getting lurching on the shift then you are probably backing the throttle off too far during the shift.

 

If you learn to shift your boxer bike without using the clutch on the up-shift, that is how you need to control the throttle during the shift, so just do the same thing using the clutch & it will smooth right out on the shifting.  

 

Or, some riders only partially de-clutch for the shift by only pulling the clutch lever partially in  (as a rule I don't so this but it can  help shifting smoothness). 

 

Even to this day I typically don't use the clutch on my boxer bikes for light & moderate throttle upshifts from 2nd through 6th. (smooth as silk). I do (usually) use the clutch for full throttle upshifts. I also typically don't use the clutch for 6-5, 5-4 downshifts, but do usually use the clutch for 2-1 down shifts & the 3-2 downshifts can go either way. 

 

 

 

 

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dirtrider
12 hours ago, JamesW said:

I am totally confused about how the clutch switch works on a BMW oilhead.  My bike is a '93 so the clutch switch is located in the clutch assembly.  My bike starts and runs the same with the switch connected or not.  What is the purpose of this switch.  The switch simply applies a ground to the starter relay when the clutch lever is pulled in and I can't see what this is supposed to do or how it does it.  So, I need enlightenment. 

 

Morning James 

 

I put this in it's own posting__

 

The clutch switch & the transmission neutral switch parallel each other (both can provide the ground path for the starter relay pull-in coil) 

 

In it's simplest form that is ALL the clutch switch does is provide a ground path for the starter relay pull-in coil. It has no input into the Motronic, can't/doesn't change  anything  in the fueling control (it is just a simple start-inhibit by-pass switch)

 

The big difference between the clutch switch & the  trans neutral switch is that the trans neutral switch "also" illuminates the dash neutral light. If the clutch switch wasn't isolated from the neutral light circuit,  & seeing as it parallels the neutral switch, if the clutch switch wasn't isolated  from the neutral light then the dash neutral light would also come on every time that the clutch lever was pulled in. 

 

SO, there is a one way diode in the clutch switch circuit so it can ONLY parallel the neutral switch for starter relay pull-in coil grounding but NOT turn on the neutral light (this is what makes the clutch switch circuit seem so intimidating to most).

 

ALL the clutch switch does is provide a ground for the starter relay pull-in coil when the clutch lever is pulled in (that's it).  

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JamesW

Hi D.R.,  Yes, I pretty much figured all that out.  When I first looked at the wiring diagram I thought I saw a connection to the ECU that involved the clutch switch but that turned out to be my error probably as a result of using my drug store reading glasses since I lost my prescription glasses in the brush last week. Grrrrr...

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