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smoothing the throttle at low speeds


oops

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Hey Folks,

I seem to be having trouble applying power smoothly at low speeds, particularly in 2nd gear. The bike (99RT) wants to leap ahead all of a sudden causing me to back off on the throttle which then causes the bike to jerk in the other direction; this is not comfortable. Is this just my lack of riding skill or what?

Oops

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Can you provide a little more info? You say it happens at low road speeds, but what about engine speed? Does it happen when transitioning off idle? When rolling up from low revs, like 2000? Or when accelerating from cruising revs like 3000-4000 to higher speeds? Does it happen when accelerating hard or gently?

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Perhaps the throttle cable adjustment at the grip housing is too tight. It can be loosened such that the response is a little slower when you twist the grip. Might check it out.

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Okay so this is low revs and going from the no or almost no throttle position. Most often I get this in town when leaving a stop light and turning. I want to accelerate smoothly and the bike just sort of lurches forward on me.

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My bike did the same, called a snatchy throttle, often found 0n fuel injected bikes. Something that helped, not cured, helped me was to put an o ring between the grip and the housing which same caused a lot of friction resulting in smoother control and a cruise control of sorts. Still there 50,000 miles later but not as good at cruise control, now the bike slows down gradually as I ride with my hands off. About 2 miles later it is at idle rpm.

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Peter Parts

Is it mechanical issues in the throttle or is it the TB and fueling?

 

 

Throttle will be smooth with a counter-force spring.

 

Fueling issues may be too low an idle speed or too little air through BBSs (there are multiple equivalent ways to synch but only one configuration will mate with the ECU maps).

 

Anybody done something dumb like touch the factory-set idle stops screws?

 

Ben

 

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Morning Oops

 

Difficult to tell what you have going on there as we can't see or ride your bike.

 

Your snatchy throttle control could be anything from sticky throttle cables, to a sticky twist grip, to incorrectly adjusted throttle cables, to something engine or engine fueling wise like TB adjustment or worn out throttle shafts & bushings, to possibly your operation & modulation of the throttle, or even normal BMW large throttle plate light throttle control.

 

Maybe start by slowly & smoothly twisting the twist grip (engine not running) to see if you can feel any stickiness, binding, or jumpiness. If so try to find out what & where it is sticking. Sometimes soap & road grip will work it's way between the twist grip & handle bar causing a sticky twist grip. Also check for proper gap between the twist grip & bar end weight (if too close that can cause a sticky twist grip).

 

While it really isn't recommended to lubricate the BMW cables or twist grip I have found that a product like Tri-Flow (Teflon based) works wonders to free up & smooth out sticky BMW cables & twist grip. The Teflon type lubricant doesn't swell up cable liners or attract dirt like petroleum based cable lubricants do.

 

It wouldn't be a bad idea to PROPERLY set the throttle cable free play & adjustment as a starting point. Too much free play can make throttle control iffy at best.

 

Next, you should check to see if BOTH side TB cams lift off their idle stop screw's at EXACTLY the same time (with choke off) as the twist grip is slowly opened. Then make sure that both throttle cams hit the wide open stops at the same time. If not then you need a TB balance or adjustment or at least a check by a qualified person.

 

If you still don't think your throttle control is working smoothly or correctly stop by a BMW dealer & have them take it for a ride. At least that way you will know if the problem is the bike or you. In any case that will give you an idea what needs to be worked on.

 

Otherwise--if you post your location maybe someone on the site here can meet you & test your throttle for proper action based on their bike.

 

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Both my '98 RS and '02 RT have 'snatchy' throttles just like you are describing. Nothing has worked so far...

On the RS, I have, over time, rebuilt the TB, got a good sync, good valve adjust, new fuel filter, new cables - you name it. The problem is that when you close the throttle, the F/I shuts off the flow of gas...therefore a lurch. Then when you open the throttle again, the drive line snatch makes you lurch in the other direction. The only thing I am not positive about is the throttle cable slack. And I have played with that multiple times over the past 10,000 miles.

Does anyone else have a smooth 1100 or 1150?

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roger 04 rt
Both my '98 RS and '02 RT have 'snatchy' throttles just like you are describing. Nothing has worked so far...

On the RS, I have, over time, rebuilt the TB, got a good sync, good valve adjust, new fuel filter, new cables - you name it. The problem is that when you close the throttle, the F/I shuts off the flow of gas...therefore a lurch. Then when you open the throttle again, the drive line snatch makes you lurch in the other direction. The only thing I am not positive about is the throttle cable slack. And I have played with that multiple times over the past 10,000 miles.

Does anyone else have a smooth 1100 or 1150?

 

With the mixture set to 13.8:1 using the LC-1 the throttle on my 2004 R1150RT is pretty smooth and not snatchy. Before adding the Wideband O2 I felt the throttle was pretty sensitive at low gear low RPM.

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Again, I have to say - DO NOT GO CHASING COMPLICACTED SOLUTIONS to what may be an easily remedied problem. Check your throttle cable, maybe do a sync if that doesn't help, and then go on from there. You can P away a lot of time and $ chasing things that, per posts here, DO NOT HELP ANYTHING! FWIW, and IMO!

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Don't slam the throttle completely off and back on. Leave it slightly rolled on, maybe fast idle worth, and it will behave smoother. YMMV.

 

----

 

 

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The RT has a pretty quick throttle and those big jugs have lots of engine braking. Check the idle RPM and try 1150. You might also press your hand up against the switch module to produce a little drag.Don't suddenly shut the throttle down. Practice on smoothness. You will get better at it.

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roger 04 rt

I find it interesting that BMW's instructions for adjusting idle and low throttle settings on the non-CAT European R1100s is to adjust the CO potentiometer for an AFR in the range: 13.77 to 14.11 (CO 1.5% +- 0.5%). Surely that must lead to better low RPM behavior. Why else why didn't BMW just set the non-CAT mixture to 14.7:1 just like the US bikes?

 

 

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I find it interesting that BMW's instructions for adjusting idle and low throttle settings on the non-CAT European R1100s is to adjust the CO potentiometer for an AFR in the range: 13.77 to 14.11 (CO 1.5% +- 0.5%). Surely that must lead to better low RPM behavior. Why else why didn't BMW just set the non-CAT mixture to 14.7:1 just like the US bikes?

 

 

Morning Roger

 

That is actually pretty tight specs. One of my Ducati's of that era have a European Co. spec of 1.5-4% Co (set with ECU fuel trimmer screw & air by-pass screws)

 

Interestingly enough the service manual (as close as I can translate it) says if needed to sacrifice perfect air flow balance in favor of a uniform mixture. The ECU uses a single idle fueling trim screw (similar to the BMW idle trim pot) but separate idle air by-pass screws.

 

Another interesting statement is-- as a final test, short out one spark plug then the other while watching the rev counter (tachometer to us Americans) to verify the same engine torque at idle.

 

Seems they agree with what we (you & me) have talked about in the past on even fueling over even air flow at idle.

 

What the Ducati has over the BMW is a separate Co. tap on each exhaust pipe so the cylinders can be sniffed separately.

 

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roger 04 rt
I find it interesting that BMW's instructions for adjusting idle and low throttle settings on the non-CAT European R1100s is to adjust the CO potentiometer for an AFR in the range: 13.77 to 14.11 (CO 1.5% +- 0.5%). Surely that must lead to better low RPM behavior. Why else why didn't BMW just set the non-CAT mixture to 14.7:1 just like the US bikes?

 

 

Morning Roger

 

That is actually pretty tight specs. One of my Ducati's of that era have a European Co. spec of 1.5-4% Co (set with ECU fuel trimmer screw & air by-pass screws)

 

Interestingly enough the service manual (as close as I can translate it) says if needed to sacrifice perfect air flow balance in favor of a uniform mixture. The ECU uses a single idle fueling trim screw (similar to the BMW idle trim pot) but separate idle air by-pass screws.

 

Another interesting statement is-- as a final test, short out one spark plug then the other while watching the rev counter (tachometer to us Americans) to verify the same engine torque at idle.

 

Seems they agree with what we (you & me) have talked about in the past on even fueling over even air flow at idle.

 

What the Ducati has over the BMW is a separate Co. tap on each exhaust pipe so the cylinders can be sniffed separately.

 

Hi DR,

That 1.5-4.0% range translates to an idle AFR range of about 14:1 to 13:1, an idle mixture range I've seen for other SI engines. and we're in agreement that if you balance the air with a good normal tune, then adding or somehow balancing fuel will make a good improvement.

 

Separate monitoring of the exhaust gas, like on the 1200s, would be great but maybe a bridge too far for the 1100s and 1150s.

 

Given the Ducati and BMW European configurations, it seems pretty easy to connect the dots and conclude that each company tuned for richer mixtures when it didn't have to meet EPA requirements.

 

That said, I think the first steps for Oops are to make sure the bike is tuned and the cables are adjusted--and maybe a couple tanks with Techron concentrate added to the fuel. And to take some time to get used to the feel of the bike.

 

RB

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----Separate monitoring of the exhaust gas, like on the 1200s, would be great but maybe a bridge too far for the 1100s and 1150s.

 

 

Morning Roger

 

Just so we are on the same page here the Ducati has separate Co. taps (pipe plugs) for each exhaust pipe but no 02 sensors (open loop bike). That allows each cylinder to have the Co. adjusted separately for each cylinder.

 

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roger 04 rt

 

----Separate monitoring of the exhaust gas, like on the 1200s, would be great but maybe a bridge too far for the 1100s and 1150s.

 

 

Morning Roger

 

Just so we are on the same page here the Ducati has separate Co. taps (pipe plugs) for each exhaust pipe but no 02 sensors (open loop bike). That allows each cylinder to have the Co. adjusted separately for each cylinder.

 

Hi DR, Got it, nice arrangement!

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My 800ST was like that when I first got it . HAd to retrain my right hand. A good tune up as suggested may correct the problem.

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