stainless brake line and high idle

[raphski]

Hi,

My front brake line is looking in need of replacing. From what I can gather it seems stainless is the suggested approach. Is there is a particular manufacturer that some of you have used and would recommend.

On another topic I have also intermittently experienced the high idle so will pay more attention to the recent thread when I have a chance. I notice mine when I get home from a ride. The last half mile home is down hill on a gravely dirt road so I'm usually going pretty slow and using the engine to control speed on the decent.    

[motoboy66]

I ordered Hella lines for mine. But they weren't off the shelf, had to measure and specify the fittings on their custom order website.

Mine also has the intermittent high idle. There seem to be multiple threads on it.

It's currently my biggest niggle and i've i'm getting tempted to blindly order the Siemens bean can.. At least it's no longer shooting fireballs at unsuspecting cyclists out of the RH exhaust pipe.

[Barry]

The recent thread on high idle suggest you should start simple and just reduce the idle speed when the engine is fully warmed up after min 10 mile ride. Only if that doesn't cure the problem consider that the cause may be more complex.

The reason for a long warm up is not only does the engine have to be up to temperature in terms of the combustion efficiency but the engine and transmission oils need to be at proper operating temperature which reduces their drag on the idle speed.

[nhmaf]

I once ordered some stainless brake lines from Bob's BMW in Maryland - they had them made by someone who did a good job - I gave them the model, year, and handlebar height and brake info for my R65LS, and they had them shipped to me in 1-2 weeks.  Fit perfectly.

I've also gotten some from Spiegler, which also worked well.

[tunnelrider]

Nice rounded post Barry regarding the high idle and also why it takes so long to warm up the whole engine, it explains why engines tend to warm up a lot quicker going uphill - I guess the gears are under a lot more load.

I agree, high idle rev is easily fixed with a bit of playing with both the throttle stop screws and idle mix under the carbs.  I've found that the idle mix screws under the carb actually alter the economy of the engine a reasonable amount, i.e. how many km I get per tank. The initial setting of the idle mix screw, under the carb, you should start with raphski is 3/4 a turn from the seating. The seating being tightening the screw to where it will not turn, but do not force it any tighter. Then loosen it out 3/4 from the initial position. A felt or wooden pencil will help to mark the initial spot.
Then read this:

http://www.bmwr65.org/htdocs/yabbfiles/Attachments/Tuning_40mm_BING_CV_carburetors_for_BMW_motorcycles_by_ear.pdf

[motoboy66]

My high idle is only after letting off the throttle.. then after anything from 10 seconds to a minute it settles back to it's normal steady beat. Mixture seems set about right and there are no air leaks between the carb and engine. I do have hardly any back pressure on my exhaust system and have  filter pods straight on the carbs with no air box so it may be affecting the setup adversely. The advance weights seem to be moving freely enough BUT there is some light corrosion on the posts that they pivot on which could be causing them to drag possibly? That's my best guess at this point!

[jonathanrowley]

i'm getting tempted to blindly order the Siemens bean can..  

Worked a treat for me

[mrclubike]

The throttle shaft "O" rings could be swollen and causing the shaft to hang up
It doesn't take much  

[Barry]

A sticking throttle shaft is certainly possible and would mimic one of the 2 fundamental causes of idle speed hang up:

1.Mechanical hang up of the advance mechanism.

2 The idle speed is set too high because the mixture screw setting is incorrect.


Mechanical hang up definitely happens but is as not as common as might be imagined or at least not the most common cause. The mechanism at work for this cause though is very obvious. Ignition timing at idle is a compromise between easy starting and efficient idle so that more advanced timing resulting from a sticking advance will increase idle speed.


The mechanism at work with Carb related idle hang up is less obvious. . Carb related idle hang up occurs when the transition ports are brought in to play because the butterfly is too far open at idle.  The transition ports are the two tiny holes close to the butterfly's bottom edge. They get fuel from the pilot jet circuit but aren't controlled by the pilot mixture screw, they are controlled by the position of the bottom edge of the butterfly as it moves over the holes creating a sufficient depression to draw fuel. They are designed to smooth the transition from the idle circuit to the needle circuit.

With the butterfly at a proper idle setting and at wider throttle openings the transition ports are not in operation as the edge of the butterfly is not close enough to create sufficient vacuum but if the butterfly is further open than it should be at idle the transition ports can begin to flow fuel and increase the revs.

The butterfly might be too far open because the idle speed has simply been set too high or it might be because the idle mixture is incorrect and more throttle was used to compensate.

Either way the simple test is to move the butterfly away from the transition ports by reducing idle speed using the throttle stop screws on both carbs, even if that means going lower than usual or desired. If the idle hang up is resolved then you know it's carb related and can re-tune the idle mixture. If not then you only wasted a couple of minutes and can move on to looking at the advance mechanism.  

[D Mann]

I had high idle when the engine was warm, mentioned it at a tech day, we balanced the carbs and no more problem. I was surprised, was expecting bean can or cable/linkage problems, but a proper balancing was all it needed.

[marcmax]

I have had an intermittent high idle issue for about 4-5 months now. Not all the time but always after the bike has had a good warm-up period. Ocassionaly I will get a high idle when I back off the throttle when stopped. If I slip the clutch (I know that is not a good solution) it will drop the rpm's and they stay at a normal range until it happens again. Not all the time.

[Barry]

, ...but a proper balancing was all it needed.

yes, especially if that included mixture screw adjustment.

[motoboy66]

The carbs on mine have both been totally rebuilt at this point with fresh o rings throughout. I will take some time riding and tweaking as it this point the whole rebuild only has about 100 miles on it and it's my first air head.

Balancing the carbs is feeling like a black art to be sure and i'm still waiting for that eureka moment.

[Barry]

...Balancing the carbs is feeling like a black art to be sure and i'm still waiting for that eureka moment.

That brings to mind Duane Ausherman's comments on the subject. When he ran a BMW dealership, seeking perfection in carb balance used to drive his mechanic's crazy.

"The bottom line on carb tuning for the BMW twin

A good BMW twin tuner with a lot of experience will almost never find a perfectly tuned engine.  Each of my mechanics went through a "crazy period" when they were learning to tune carbs.  While riding their own bikes, every few minutes they would reach down and do a slight tweak on a carb.  Eventually, they learned to accept that it would never be perfect.  The very best that you will ever achieve is a workable compromise.  Be happy. "

  

[Luca]

I agree, high idle rev is easily fixed with a bit of playing with both the throttle stop screws and idle mix under the carbs.  I've found that the idle mix screws under the carb actually alter the economy of the engine a reasonable amount, i.e. how many km I get per tank. The initial setting of the idle mix screw, under the carb, you should start with raphski is 3/4 a turn from the seating. The seating being tightening the screw to where it will not turn, but do not force it any tighter. Then loosen it out 3/4 from the initial position. A felt or wooden pencil will help to mark the initial spot.
Then read this:

US bikes are jetted differently.  The base settings for our bikes are closer to 1-3/4 turns out.