setting throttle body baseline Dirtrider help

[SANTA]

background r1100s with motronic 2.4, twin spark with 48000km

as far as i know the TPS and the idle stop screw on the left side have never been moved.

 

over time as miles have piled on it would require more and more RH BBS to get an even balance at idle. and the high speed syn was funny, it would change from left to right, it would not hold steady.

 

i came to the belief that one of the idle stops screws had somehow moved, the only solution to set the both BBS screws to 1.25 turns out and then use the right idle stop to achieve manometer balance.

 

i have done that and it runs very well now, with only ONE ISSUE;

 

when the throttle is rolled on to accelerate, one can feel just the slightest left/ right imbalance initially, almost like a single cylinder engine accel, don't know were to start to correct this.

 

suggestion are requested, Oh and its -30deg outside right now, the garage is a freezer, so nothing is going to happen for a while but i want to make this go away

 

thanks

 

 

 

[Michaelr11]

Remove and clean both of the big brass screws, then remove the hose from the bottom and spray O2 sensor-safe TB cleaner into the air bypass ports until you get clean run-through from the bottom.

[dirtrider]

Morning Santa

 

The idle stop screws are pretty solid & I haven't ever seen them move by themselves.

 

The usual cause of an erratic balance, or changing balance side to side is worn throttles shafts, or worn throttle shaft bushings, or cables with kinks in them, or loose TB's in their boots, etc.

 

Personally I think riders pay way too much attention to getting an even air flow balance while missing more important things.

 

Even side to side fuel flow is way more important than a bit of air flow difference. Problem is, no good way to measure or verify "even" fuel flow.

 

On the TB balance, one of the most important things is to verify that both throttle plates open at the very same time (basically lift off the idle stop screws at the very same time). If the idle stop screws are not set correctly that is difficult to verify & correct. The idle stop screws were supposedly initially set at original build by throttle plate opening angle. (difficult to check that at home). About all you can do is get it close by using air flow delta (vacuum difference). This only works to get it close unless the engine is EXACTLY the same side to side on cam profile, cam timing, valve adjustement, compression, intake restriction, exhaust restriction, cylinder head machining, etc.

 

When you see something like the balance continually changing from left to right look for tight or damaged cables, or worn throttle shafts or bushings, or loose or worn throttle plates. OR, maybe something mechanical like excessive coking of the intake or exhaust valves, or a slight exhaust restriction on one side.

 

On your " when the throttle is rolled on to accelerate, one can feel just the slightest left/ right imbalance initially, almost like a single cylinder engine accel, don't know were to start to correct this"---

 

I'm not sure how anybody could feel or tell a slight side to side imbalance on acceleration from just riding the bike. Could just as easily (actually more likely) be a fueling issue or one of your stick coils dropping out momentarily under increased engine loading.

 

If possible try to borrow a set of known good stick coils as a quick test.

 

You might also check your 02 sensor wire pig tail routing. If that is routed close to or along your R/H lower spark plug wire it can pick up cross talk from the plug wire & drive the fueling crazy for a short time.

 

Bottom line here: don't get so stuck on correcting a slight TB imbalance that is pretty meaningless while overlooking more important things like stick coils or a fueling issue, or other engine mechanicals.

 

[SANTA]

what started this all off is a 1998 r1100rt, that was dropped er set at my doorstep with the request to check it out, claiming a a gearbox rattle. to make it a short story, this bike had been maintained by a bmw mechanic and was so smooth i couldn't beleive it... especially in the initial throttle rollon,

 

i guess trying to get mine back to that state is the search.

 

i will add some additional info, the o2 sensor died and was replaced, and just before being parked i had the injectors cleaned.

 

have tested a spare stick coil no change. id expect the stick coil to ail at higher rpm with a very warmed up engine

 

thanks for the suggestions