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Old 05-15-2015, 09:34 PM   #1
marbee40 OP
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Leaking throttle body?

02 GSA. Rebuilt left TB 2 years ago and right TB last winter using Cata Dan's kits. Both TB shafts are tight with zero clattering.

I've been having issues with TB syncing for the last year. Bike will only run halfway decent with the left TB brass screw at 1/4 turn (vice 1.5). In other words, super lean. Another issue is popping on decel.

Last night I finally got fed up and started poking around. Left TB was showing a weep of fuel on the inside near the cable slide...as if it were coming out the shaft past the o-ring. Using a lil starting fluid RPM's would climb to about 2k. I verified no other leaks at either the front or back of TB.

Pulled TB apart and o-ring looks fine but definitely fuel getting by. If fuel is getting out, air is getting in.

Should I only replace the o-ring? Where to find locally? BMW?
Thanks,
Jim
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Old 05-16-2015, 12:54 AM   #2
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When I rebuilt mine, I used a combination of o-rings and the original seals.
Still going good maybe 20000km later?
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Old 05-16-2015, 08:47 AM   #3
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Original 'seals'?
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Old 05-17-2015, 08:24 AM   #4
gr8ridn
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Quote:
Originally Posted by marbee40 View Post
Original 'seals'?
Don't overlook what BMW calls the throttle stub pipe. This is the rubber tube between the cylinder head and the throttle body. These typically crack and develop leaks with age. This means un-metered air introduced giving the symptoms you describe. You might try testing for leaks. First ckeck the stub pipe clamp and mount screws. I spray WD 40 around the stub pipe with the engine warmed and idling. If it is leaking the the idle speed will pick up in response to enriching the intake mixture.. WD 40 is much safer than other combustibles like gas, starter fluid etc. Do this outside the garage, it doesn't take much fluid to discover leaks.
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Old 05-17-2015, 05:46 PM   #5
def
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If fuel is present at the shaft/bushing location, I would suspect your fuel injector(s) may be leaking after shut off. A cleaning may solve the issue. Fuel injectors should shut off drip tight.
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Old 05-17-2015, 10:58 PM   #6
marbee40 OP
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Gr8rdn, no leaks at the stub pipe. Even took it off and inspected. Still pliable with no cracking.

As for the fuel injector comment, I'll clean that up asap.
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Old 05-18-2015, 06:55 AM   #7
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Originally Posted by marbee40 View Post
Original 'seals'?
You're testing my memory now.
It had rubber things, kind of like an o-ring but thinner and flatter, sort of cupped.
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Old 05-18-2015, 08:09 AM   #8
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This is the kit...

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Old 05-18-2015, 08:41 AM   #9
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Originally Posted by gr8ridn View Post
Don't overlook what BMW calls the throttle stub pipe.
I thought they called this the "intake manifold" or "inlet manifold", no?
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Old 05-18-2015, 10:46 AM   #10
def
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Excerpted from the BMW REProm;

Removing and installing trottlevalve
stub pipe
Press in spring keeper of multi-pin plug for throttle-
valve potentiometer (1) and disconnect plug.


They spell it two ways...interesting.
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Old 05-18-2015, 10:48 AM   #11
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This is the kit...

I'm interested to know why the flat is milled on the outside of the shaft at the throttle plate slots....Hmmmm.
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Old 05-18-2015, 11:02 AM   #12
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Originally Posted by def View Post
I'm interested to know why the flat is milled on the outside of the shaft at the throttle plate slots....Hmmmm.
Good question. I wonder if it is simply because it is easier to machine an entire flat, as opposed to flats only where the bolt heads and nuts are seated.
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Old 05-18-2015, 11:14 AM   #13
def
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Quote:
Originally Posted by marbee40 View Post
02 GSA. Rebuilt left TB 2 years ago and right TB last winter using Cata Dan's kits. Both TB shafts are tight with zero clattering.

I've been having issues with TB syncing for the last year. Bike will only run halfway decent with the left TB brass screw at 1/4 turn (vice 1.5). In other words, super lean. Another issue is popping on decel.

Last night I finally got fed up and started poking around. Left TB was showing a weep of fuel on the inside near the cable slide...as if it were coming out the shaft past the o-ring. Using a lil starting fluid RPM's would climb to about 2k. I verified no other leaks at either the front or back of TB.

Pulled TB apart and o-ring looks fine but definitely fuel getting by. If fuel is getting out, air is getting in.

Should I only replace the o-ring? Where to find locally? BMW?
Thanks,
Jim
The BBIABPSs are there to adjust idle air and allow one to balance the TBs at idle RPM. However, the setting of 1.5 (or is it 1.25) turns assumes the throttle stop screws are in specification.

If you are unable to achieve correct TB balance at idle RPM within the BMW recommended turns off seat for the BBIABPSs your TB(s) throttle stop set screws are out of adjustment and you have violated the BMW blue paint on these screws and the Bing folks are coming for you.

The 52mm X 2mm o-ring at the intake end of the TB has no influence on idle air. You might check the 7.5 X 3.5 o-rings on the BBIABPSs for leaks. Also, the stubs (or intake manifolds as they are referred to on the Max site) should be checked for leaks. I apply some silicone grease to them when refitting the TBs.

Realize, these BBIABPSs have no influence on engine operation (mixture) once you are off idle.
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Old 05-18-2015, 11:21 AM   #14
def
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Quote:
Originally Posted by MaxSeven View Post
Good question. I wonder if it is simply because it is easier to machine an entire flat, as opposed to flats only where the bolt heads and nuts are seated.

What purpose does the flat serve? Many throttle shafts in other applications have no flat at all and some eliminate the lock nut altogether. Some race applications attempt to eliminate fasteners completely thereby eliminating ingesting metal parts into the intake track...especially in blower setups. I've seen blowers that have been damaged by a screw that came loose...expensive.
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Old 05-18-2015, 11:46 AM   #15
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Quote:
Originally Posted by def View Post
What purpose does the flat serve? Many throttle shafts in other applications have no flat at all and some eliminate the lock nut altogether. Some race applications attempt to eliminate fasteners completely thereby eliminating ingesting metal parts into the intake track...especially in blower setups. I've seen blowers that have been damaged by a screw that came loose...expensive.
Unknown - maybe the flats reduces airflow turbulence at WOT?
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