Yet Another TB Sync Note

Typical to many oilheads, this bike's carbon canister must've vibrated off and got lost down the road somewhere... so the throttle bodies' bottom vacuum ports are properly capped off.
Closing out a minor service this afternoon, I pulled the caps to check the throttle body & cables balance. To help avoid losing them, I put them on a white paper towel. After readjusting one of BBSs a little, I looked at the towel - and there was some wet crud absorbed from the caps.
So - there's another place to clean out tarpiculates. Get a Q-Tip into the insides of the caps and give 'em a swipe!

You can also use short lengths of vacuum line of the appropriate ID and plug the ends which are not on the t/b nipples with a machine screw and then tie wrap the screws so they don't fall out

Crap post butterfly plates is bad

If you are getting a hard, kinda carbon looking/pencil lead kinda crap, you are burning ethanol whether you realize it our not. What you are seeing is the ethanol taking the phenols out of the gasoline. That crap only builds after the engine cools, not while it's operating. Bosch suggests the use of an approved gasoline fuel conditioner, like Chevron's Techron. The bad news is the throttle bodies are the first to suffer with lazy throttle response and the need to sync every few months. It's possible that you can't get a significant low idle, under 400 rpm. I can get my R1100RT to sit that low and that's where I set my big brass screws. The really bad news is that if you ignore it and find a backyard fix to get you by, that accumulation will be on the valve stems and eat the guides. That's a slow process. Now for the really bad news, if one of those accumulations comes off the stem and catches the valve seat, while hot and operating, it will stick to the valve seat. Once the engine cools, that hard crap will imbed into the seat and with about a season of riding, burn the valve.
This has been an issue in Canada for quite some time now. It's not BMW unique. Sometimes that crap will cause a transient discharge in poor TPS, just like a Beemer TPS and you can't get a low voltage for idle twice in a row and condemn the TPS, only to have it happen again.
If you pull your injectors and get them tested suspecting you have a lazy seat in the injector, the heat shield often looks very good and flow is perfect. When you take the filters out of the injectors, they are usually brown and hard. That's the clue, ethanol.

Definitely good info for all, thanks! There are other posts in this forum about valve damage due to ethanol; yeah we have it too, grrr...

I had cleaned off the tips of both brass screws; one side was "typical" and not bad at all, but this side also had some gunk on it. I also cleaned out both idle passageways. The stuff I got out of the cap was a mix of thin (and quickly evaporating, so it was prob'ly the gas I used for cleaning) and thick (oily goop buildup), plus just a little bit of dark grainy stuff. Since this is the "lowest" point, possibly the tube also acts as a bit of a trap or sump.

Chevron is pretty popular around here, it's known that Techron is actually good. When the local auto parts stores here have special sales on Techron or Sea Foam, they sell out pretty quickly, since our gas is so sucky. We have several refineries nearby, but much of their product is actually aviation fuel or goes to the military

Chevron IS Techron or perhaps I should say Techron is a Chevron product. Either way, doesn't matter, other than it works great as a fuel system "maintenance" cleaner. Meaning, if your system is already fairly clean due to regular weekly use and miles ridden regularly Techron works very well. Just don't assume that if you have fuel related problems, like a gummed up system or rusty fuel pump, due to the bike not being ridden for years, don't expect Techron or any fuel cleaner to get it to normal conditions.

But I stand by regular repeated use of Techron as my 94 RS has had not one fuel system issue and its still on the original injectors, fuel pump, fuel regulator etc. Runs great and very smooth.

I would expect the BBS tip on the side of the bike nearest the crankcase vent line to be more "oily" kind of grime, that is perfectly normal. WD40 works well for cleaning the BBS and the port.

Yeah, everything cleans up pretty easily, but a note for folks to be aware of:
Do not let cleaning solvent get on the little O-ring, it may deteriorate the rubber. If it cracks, you now have a non-repeatable air leak that will make it difficult to get a good idle sync.
Also do not let any lubricant get on the O-ring - it is responsible for firmly holding the idle air adjustment, and if lubed, the engine vibration, plus heating & cooling, is enough to move it over time.

Dieselyoda said:

It's possible that you can't get a significant low idle, under 400 rpm. I can get my R1100RT to sit that low and that's where I set my big brass screws. .

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why in the world are you interested in setting your idle at 400 rpm?

Factory setting for the idle is 1100 to 1200 rpm. NO reason to set the idle lower than that. Keep in mind that oil distribution and cooling, especially on a stationary bike, is dependent on rpm. Less rpm, means less oil moving through the cooler, means faster heat gain in the engine. I don't see why you'd want idle speed any more than 10% below factory recommended values. At most (least) the idle speed could be 1000 rpm.

Unless you back the cable slack way off and back out the factory set (and painted/sealed)idle stop screws I doubt you can get much below an idle speed of 800 rpm just with the BBSs.

Dieselyoda said:

If ... Bosch suggests the use of an approved gasoline fuel conditioner, like Chevron's Techron. The bad news is the throttle bodies are the first to suffer with lazy throttle response and the need to sync every few months. It's possible that you can't get a significant low idle, under 400 rpm. I can get my R1100RT to sit that low and that's where I set my big brass screws. ...

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I didn't realize that Bosch recommended Techron but use it regularly. Even when it has only been 6 months I notice an idle speed increase by the time a half tank, with the concentrate added, has been consumed.

I'd like to hear why you try for a 400 rpm idle.

Make sure you squeeze that rubber cap used to seal the TB port and check it for cracks. Recently my RT was running kind of rough and it turned out to be a vacuum leak coming from the cracked, deteriorated rubber cap. They are constantly exposed to hot/cold conditions and the rubber breaks down; they get leaky. Just a little FYI.

I've also found that the caps we can buy at the local auto parts stores do not last as long as the BMW caps. We do operate in a more severe environment.

Pauls1150 said:

I've also found that the caps we can buy at the local auto parts stores do not last as long as the BMW caps. We do operate in a more severe environment.

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I get a year or less life out of auto part store caps and more than five year life out of the BMW OEM caps. The caps I buy are the ones specified for the vacuum take off ports on the throttle bodies on K75/K100/K1100 bikes.

I've considered that rather than using the rubber caps using 3-5 inch pieces of hose capped with screws. This way, I could do or check the throttle bodies at anytime by simply hooking up the twinmax to the extensions which could be tucked into the faring. Only issue is getting to the BBS on the left side with the fairing on. Probably could cut a nice hole in the left fairing and cap it so it looks more professionally done.

OLSENSAN said:

I've considered that rather than using the rubber caps using 3-5 inch pieces of hose capped with screws. This way, I could do or check the throttle bodies at anytime by simply hooking up the twinmax to the extensions which could be tucked into the faring. Only issue is getting to the BBS on the left side with the fairing on. Probably could cut a nice hole in the left fairing and cap it so it looks more professionally done.

Click to expand...

If you want to do that just use 12" or two feet of hose routed to wherever you want it for convenient access.

Low idle is a very big deal

My comments aren't specific to BMW nor should they be as there isn't one system on a BMW that's unique to the manufacturer. A low idle, below normal with a very good set of gauges, be they water, mechanical or mercury can give you a great picture of what is going on inside and outside any given cylinder. From a very low idle, as low as it will go, you should be able to get a good idea of the following and my list isn't inclusive:

Ignition Timing, relative and actual
Valve Timing, relative and actual
Valve condition, stretched valve or worn lifter/lobe
Injector/Carb condition
Exhaust condition
Ignition condition, lazy spark plugs
Piston Ring Condition.
Atmospheric air leaks.

I can't remember them all but it's a pretty important old-guy starting point when you are looking at an engine. If you get caught up thinking that this engine using crankcase oil is an important factor, I can introduce you to at least ten other engines using oil cooling.

If you believe that a scan tool can tell you when a valve has stretched, have I got some news for you.

I can make sense of using a low idle as a diagnostic tool (if one knows what to look & listen for and knows what it means), but I can't imagine operating the bike at such a low settting as SOP.

I guess my posts have been a bit confusing. The very low idle is my starting point to sync carbs/throttle bodies. If I can get my gauges equal and steady, I'm pretty comfortable that the rest will be a breeze. I think of it as setting idle mixture and then move on to curb idle. If curb idle remains equal and steady on the gauges, I'm pretty comfortable that setting the mid-throttle sync will be even easier. What most of you have been talking about is the curb idle and in my opinion, if you sync at curb idle, you can miss some very important clues as to the overall condition of your engine.

My 96, R1100RT has a custom feramic, four pad clutch plate for incredible hook up and the OE "recommended" setting of 1100-1200 rpm curb idle will cause the bike to launch so I have it sitting, curb idle, at 850. I've also noticed the OE idle setting will cause the engine to build heat very fast in stop and go traffic and that concerns me.

I hope that clears some confusion.