Throttle body sync, cable slack ??

[Rapala 50]

I have read a lot of the threads on here about doing the TBS, but fine myself a little confused about slacking the cables before making any adjustments. Can anyone tell me what this intales exactly...

[mneblett]

If your cables already have sufficient slack in them, then you do not have to do anything with them (at least not until doing the above-idle balance adjustment).

 

The idea is to ensure that when you are doing the idle adjustments, the throttle cables are not pulling up on their pulley(s), i.e., prevent the cables from ever-so-slightly opening either butterfly valve plate and thereby screwing-up the idle by-pass adjustment.

 

You check cable slack by lightly pulling up on the cable sheath down at the point the cables enter the throttle body ferrules. If there is at least a small amount of free-play as you lift the sheath, there is enough slack to do the idle adjustments. If there is no slack, loosen the lock-nut (10mm, IIRC) on the ferrule and rotate the ferrule clockwise until the cable sheath has some slack.

[dirtrider]

Afternoon Rapala 49

 

Mark covered the reason why.

 

Personally I do it differently if I need to gain some slack in the cables.

 

If you do it by loosening each side cable at the TB & moving the cable adjuster you will definitely need to do an above idle re-balance (as opposed to maybe just checking it, or knowing where it was at to begin with). The 1200 hexheads seldom need adjustment so why force yourself to have to adjust them if you don't need to?

 

If possible don't mess with the cable adjusters at the TB's but instead just back the main cable off at bit at the adjuster (under the little boot up by the twist grip). That keeps both sides even so you know how far of it was off on balance to begin with, allows cable slack to be present but not effect the cross side balance, allows the cable slack to be taken out at end of balance session without effecting the balance itself.

 

The important thing on the 1200 hexheads is not only have the above idle cross side balance set correctly but to MAKE SURE both side throttle levers lift off their stops at the exact same time.

 

[Rapala 50]

Ok, doing this throttle body sync using a home made Manometer and a GS-911 , I warmed the engine ,l locked the steppers using the gs-911 and notice the Manometer showed almost 12" difference but when I brought it up to 3500 rpm it is right on after very little adjustment to the right side. Back at idle it still shows a good foot of difference. Is this normal ?

[dirtrider]

Morning Ralala

 

12" of H2o difference at stepper held idle is a LOT. I usually find 2"-5" difference on most 1200 hexheads.

 

The BMW manual gives you a bit over 10" of H2o delta at held idle so you are not that far above the max spec.

 

You have a few choices--

 

-Live with it as it is as it isn't that far out of spec.

 

-OR, try to correct it somewhat.

 

Before doing much can you tell us how close the idle balance is with the steppers "not held"? That will maybe give us a clue on where to start the process.

 

Things to verify are --

 

*That the base idle screws haven't been messed with (the painted ones). If those have been tweaked by someone then you have a problem.

 

*That both side cables have some slack at hot engine base idle.

 

*That both side throttle levers FULLY contact the stop screws at hot engine curb idle.

 

*No leaks in the TB rubber boots or attachment to cyl heads.

 

*The engine valves are set correctly.

 

*That the engine cranking compression is close side to side.

 

If ALL above is somewhat close or in spec then you might have coked up stepper pintles or coked up pintle seats (try cleaning them with 02 safe carb cleaner.

 

Or possibly a stepper issue.

 

OR, you might have coked up throttle bores at the throttle plate areas (again try cleaning with 02 safe carb cleaner.

 

Possibly a worn throttle shaft bushing or worn shaft causing poor throttle plate seating.

 

 

___Oh, one last thing try swapping your manometer hoses side to side to verify your problem is in the bike not the manometer.

 

 

 

 

 

 

 

 

 

[Rapala 50]

After playing with the TB on both sides (not sure what the hell I was doing) for awhile. I was able to get a good enough balance between idle and off idle. I never touched anything but the throttle lock nut and adjuster. It still seemed to run a little rough at idle so I did a idle actuator sync using the GS-911 (great tool to have by the way) and it seem's to have smooth it out. Not sure about making sense of the real time values function yet but I hope to learn what it all means..

[Rapala 50]

This is what my Real Time Values looked like when I was done doing the TBS.. Anyone with some time on the GS-911 know if things look right..

This was at idle with steppers connected

[Rapala 50]

Looking at the pic. I posted it looks like the idle actuator is off by 10 or so, what would be the first thing to do to try and get this closer ? Or is this normal ? Also where exactly would I be using 02 carb cleaner, not sure I understand that process. Pic. Of these components would be a great help, I'm new to this working on my BMW thing and find this forum my main sorce of information.