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deejones

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My BMW dealer is telling me that the twin max can not be used to sync the throttle bodies,on my 051200ST. Is this correct. Thanks Dee Jones

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My BMW dealer is telling me that the twin max can not be used to sync the throttle bodies. Is this correct. Thanks Dee Jones

 

You cannot set the idle balance due to the stepper motor which takes care of idle on hexheads. You can, and many of our members do, set off-idle throttle sync with a Twinmax or indeed any other balancing tool.

 

Andy

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I don't think you should NEED to set the idle sync on these bikes thanks to Mr. Idle Control Valve.

 

You can certainly synchronize the throttle cables using a twinmax using the off-idle sync procedure (sync em just like normal only do it at 2-4k RPMS)

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My BMW dealer is telling me that the twin max can not be used to sync the throttle bodies. Is this correct. Thanks Dee Jones

 

You cannot set the idle balance due to the stepper motor which takes care of idle on hexheads. You can, and many of our members do, set off-idle throttle sync with a Twinmax or indeed any other balancing tool.

 

Andy

 

+1 to Andy's comments.

 

I have an ST and use a TwinMax to sync my carbs. Bring the RPM's up to a normal cruise, e.g., 4000 RPM, and set the sync for that.

 

Get the bike up to normal temp first, then set it. Use a fan to have some air movement over the bike while setting it as well.

 

Hope this helps. thumbsup.gif

 

You can do an idle sync but you need to park the stepper motors first. Something I haven't bothered with to this point as its running so well and smooth without.

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Well to give the dealer a little bit of credit on this one, he's correct and he's not correct.

 

You cannot do a FULL sync on the hexhead motors, because we in the aftermarket world do not yet have a way to park the stepper motors (which affect it at any RPM) prior to doing a sync. So his remark is not total BS.

 

But that being said, as mentioned you can do a usable above idle as aways.

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Phil & Jamie

When we have the SoCal tech down here in January I am so looking forward to you guys showing me how to adjust the valves and sync the TB's with my Twin Max and feeler gauge tool I made.

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Phil & Jamie

When we have the SoCal tech down here in January I am so looking forward to you guys showing me how to adjust the valves and sync the TB's with my Twin Max and feeler gauge tool I made.

 

thumbsup.gifwave.gifclap.gif

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Ken,

 

Have you tried unplugging the stepper motors and doing an idle sync per BMW's instructions?

 

The stepper motors park themselves automatically when the bike is cut off. I'd bet money that they park themselves in the same 0 position that the diagnostic computer would park them at.

 

The BMW procedure is a little funky as you are supposed to VERIFY idle sync (with the idle control system active, presumably, but the RepROM doesn't say as much). Then you adjust the throttle cables until both throttle valves open at the same time. You would want the idle control system inactive here so that you didn't get a false positive on the valves opening using the gauges, BUT, the actual position of the idle control motors wouldn't matter, just as long as they don't move.

 

Then, you are supposed to ensure that the difference between the vacuums at part-load is minimal and also that the cylinder with lower vacuum at idle has lower vacuum at part load. (There's not an additional adjustment step -- this is just a check and they tell you to go back to the previous step if it doesn't pass). This I would assume to be necessary because the idle control motors are disabled and parked at identical positions -- when active, this relative differential would be taken up. If the relative differential ISN'T maintained, when the idle control motors were reactivated, they would sync at idle but negatively impact the part-load sync. Also, the only way the relative differential couldn't be maintained, I think, is because the throttle cable adjustment is incorrect (one valve opens before the other).

 

Per the adjust at 2k or 4k or whatever procedure -- It's conceivable that, especially if the engine wasn't completely warmed up (IMO it should be in airflow from a big fan and the temperature shouldn't be changing), the idle control motors would be changing position while you are adjusting the throttle cable, giving you a reading on your vacuum gauges that would indicate your cables are synchronized when really they are not. Especially if you are adjusting at 4k, the motor is probably heating up no matter what, and so your adjustment WILL be off by however much the idle motors move while adjusting. If you do the adjustment fast enough, it would be negligable, but if you really wanted this procedure to work, I'd recommend doing it in a windtunnel (or riding to get your readings and then adjusting and then riding ...)

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Ken,

 

Have you tried unplugging the stepper motors and doing an idle sync per BMW's instructions?

Yes. I have tried - leaving them hooked up, un hooking them before I turn on the key, and un hooking them after I turn on the key. The last one because when you turn on the key you can hear and feel them go though a little initialization routine.

 

The only thing I can say for sure is that the above idle sync. is different with all three approaches. Which one is correct I'm not so sure.

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Ken -- how is the sync different depending on when you unplug them? I'm assuming you're talking about the standard BMW process -- making sure the throttle valves open at the same time using vacuum gauges -- and NOT trying to match the vacuum levels, which you shouldn't do with the idle control system disabled.

 

I'm thinking that trying to sync the TBs at 4k in a garage with a fan is actually a bad idea. It's going to heat up the engine very quickly and the idle control circuit will adjust the servo positions to compensate.

 

There's something elegant about the BMW technique of just synchronizing the opening of the valves. I think this is the right way to go. But can you use a TwinMax to do this?

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Three test runs, each measuring the vacuum at say 3000 RPM or so with a water manometer (you could use TwinMax if preferred) -

 

a) with the servos connected as normal,

 

b) With the servos disconnected before starting the bike. In an attempt to simulate the theory that the shut down parking of them is the same as the GT-1's parking of them,

 

c) With the servos disconnected after starting the bike. In an attempt to simulate the theory that the initialization of them when the key is turned on is the same as the GT-1's parking of them.

 

In each case the sync at 3000 RPM was slightly different. About a 1" on my manometer.

 

Which one, or none, of these procedures is best for the DYIer to simulate what the GT-1 does when it parks them, I do not know.

 

making sure the throttle valves open at the same time using vacuum gauges -- and NOT trying to match the vacuum levels,
I'm not sure I understand the distinction you are trying to make. Isn't the way you verify that the throttle valves are opening at the same time by measuring the vacuum levels? And then adjusting the sync if they are not?
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I attached my TwinMax to a Al. plate with suction cups so I can do under load tuning. This may not have as much effect on the coumputer RT's as my old '82, but worth a thought anyway.

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