K75S Oil/grease on throttle bodies

[ethand320]

Hi all,

I've got a 91 k75s that has some leakage around 2 of the throttle body ports.  You can see on the plugs there is some too.  For the most part the bike runs OK, has some bogging in low rpms if you open the throttle quickly (and the engine is cold).  Last season the plugs were fouled, and I changed them, but this obviously isn't a longterm fix.

Any thoughts on how to troubleshoot and repair?  I'm sure the boots on the TBs are old and could be replaced, but is that all I'm needing here?

[The Mighty Gryphon]

In my experience the K75 engine prefers to have the throttle rolled on vs. snapping it open.   

It seems to be part of the "charm" inherent in the Jetronic system and the barn door air flow sensor it uses.  The Motronic system which replaced the barn door with a throttle position sensor on the 16 valve engines has much better throttle response. 

The barn door problem is that it has a mechanical lag that allows a momentary leaning of the mixture when the throttle is opened rapidly.  Because the Motronic "senses" air flow with the throttle butterfly position the fuel delivery responds almost simultaneously with the throttle opening.

I would do a good clean of the engine followed by a valve adjustment, replacement of the crankcase breather "Z" tube, new air filter and a throttle body balance before getting into the throttle body plumbing.  Your post doesn't make me suspect any major air leaks.

[ethand320]

Appreciate the reply,  definitely will move forward with the smaller things before worrying about the TBs.  Thanks!

[rbm]

When you get around to removing the TBs and inspecting them and the bushings, remember to use red RTV or equivalent high temperature silicone sealant between the bushing and the engine block.  This will seal the bushings to the block and prevent leaks at that point.

[motohippy]

Check your crankcase vent hose (Z-tube). I've found they have a short-ish life before getting a thin split, and will both let some oil mist out and get you a vacuum leak.

[frankenduck]

In my experience the K75 engine prefers to have the throttle rolled on vs. snapping it open.   

It seems to be part of the "charm" inherent in the Jetronic system and the barn door air flow sensor it uses.  The Motronic system which replaced the barn door with a throttle position sensor on the 16 valve engines has much better throttle response. 

The barn door problem is that it has a mechanical lag that allows a momentary leaning of the mixture when the throttle is opened rapidly.  Because the Motronic "senses" air flow with the throttle butterfly position the fuel delivery responds almost simultaneously with the throttle opening.

I would do a good clean of the engine followed by a valve adjustment, replacement of the crankcase breather "Z" tube, new air filter and a throttle body balance before getting into the throttle body plumbing.  Your post doesn't make me suspect any major air leaks.

The air filter doesn't matter unless it's really, really clogged. It's a HUGE air filter for a 750cc motor. Don E covered half of the air filter with Saran wrap and it had no impact on dyno runs.
http://www.eilenberger.net/k75exhaust/

And It’s more than just the Mass Airflow and L-Jet that make K75s a bit sluggish at low RPMs. It’s the valve cams too. My K75 turbo also has Luftmeister “high performance” cams and performs noticeably better in low to mid-range RPMs. (The turbo is mid-80s turbo technology and doesn’t kick in until about 4500 RPM.)

I set the idle on my K75s at 1100+ RPM. They have less lag off of the line that way.

K75s run pretty rich at idle. If you let a K75 idle for an extended period then it will foul the plugs.

Do not start the engine and let it idle to warm up.  Start the motor and ride off right away as recommended in the BMW rider(owner)  manual.