Why is idle adjustment so convenient? | GTAMotorcycle.com

Why is idle adjustment so convenient?

TwistedKestrel

TwistedKestrel

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No I haven't been drinking yet today

Just pushing stuff around the garage, I got to thinking about how prominent the idle adjustment knob is on every bike I've had with an adjustable idle. Why is the whole linkage that makes adjusting idle easy even there? I can count on one hand the number of times an idle adjustment has ever been necessary for me, and I think it was usually in conjunction with a valve and/or sync adjustment i.e. I'm already pulling stuff off and breaking tools out. Meanwhile you usually can't even change suspension compression or rebound without producing a tool, or those same bikes could have come with control levers that have no adjustment whatsoever.
 
TwistedKestrel said:
No I haven't been drinking yet today

Just pushing stuff around the garage, I got to thinking about how prominent the idle adjustment knob is on every bike I've had with an adjustable idle. Why is the whole linkage that makes adjusting idle easy even there? I can count on one hand the number of times an idle adjustment has ever been necessary for me, and I think it was usually in conjunction with a valve and/or sync adjustment i.e. I'm already pulling stuff off and breaking tools out. Meanwhile you usually can't even change suspension compression or rebound without producing a tool, or those same bikes could have come with control levers that have no adjustment whatsoever.
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On carbed bikes used for motorcycle schools, it's usually necessary to adjust one or two bikes per year out of thirty-fourty, that I've seen. It might be more, since I'm not there all the time.

I also recall adjusting my old bike for the change in seasons.
 
Baggsy said:
On carbed bikes used for motorcycle schools, it's usually necessary to adjust one or two bikes per year out of thirty-fourty, that I've seen. It might be more, since I'm not there all the time.

I also recall adjusting my old bike for the change in seasons.
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Old school. Way back change in temp, gasoline supplier, carbon buildup, and overall state of tune could be accommodated by fiddling with idle.

I'm guessing few people reading this forum know that decarbonization was regular service on some makes.

Not so important these days.
 
Mad Mike said:
I'm guessing few people reading this forum know that decarbonization was regular service on some makes.

Not so important these days.
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These is an extremely prevalent issue again with modern direct injected cars. Ford and some others use port and direct so the valves stay cleaner while maintaining the benefits of direct. The insane carbon buildup is an issue for a lot of German DI motors. Need periodic walnut blasting because eventually the buildup will cause the valve to not even be able to seal fully.
 
TwistedKestrel said:
No I haven't been drinking yet today

Just pushing stuff around the garage, I got to thinking about how prominent the idle adjustment knob is on every bike I've had with an adjustable idle. Why is the whole linkage that makes adjusting idle easy even there? I can count on one hand the number of times an idle adjustment has ever been necessary for me, and I think it was usually in conjunction with a valve and/or sync adjustment i.e. I'm already pulling stuff off and breaking tools out. Meanwhile you usually can't even change suspension compression or rebound without producing a tool, or those same bikes could have come with control levers that have no adjustment whatsoever.
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I would play with it occasionally. Drop it as low as possible to see how carb/valves were behaving compared to just after redoing them, raise it for a bad tank of gas, raise it if going off roading or practicing tight manoeuvres so it was less likely to stall, etc.
 
KWDRZ said:
These is an extremely prevalent issue again with modern direct injected cars. Ford and some others use port and direct so the valves stay cleaner while maintaining the benefits of direct. The insane carbon buildup is an issue for a lot of German DI motors. Need periodic walnut blasting because eventually the buildup will cause the valve to not even be able to seal fully.
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Mercedes’ mechanic I socialize with says carbon buildup is the worst part of owning a sprinter van , and in some model cars , a rediculous service cost .


Sent from my iPhone using GTAMotorcycle.com mobile app
 
Is this something that was more necessary before CV carbs were common, and inertia kept it around?

Edit: Have never owned/ridden anything with slide carbs
 
crankcall said:
Mercedes’ mechanic I socialize with says carbon buildup is the worst part of owning a sprinter van , and in some model cars , a rediculous service cost .


Sent from my iPhone using GTAMotorcycle.com mobile app
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Yes it is an unfortunate reality of direct injection... it wasn't an issue for so long with everything being port injected, people are surprised when it becomes time to have the service done because your fancy vehicle is running so rough. Can easily be a $1k job. And will need to be done multiple times during ownership especially on a vehicle people put a lot of mileage on like a Sprinter.
 
My RC51 is injected but still has an idle adjuster poking out the side like a vestigial tail. I suspect it's there for the poor man's slipper clutch, i.e. jack the idle revs to about 3000...
 
Priller said:
My RC51 is injected but still has an idle adjuster poking out the side like a vestigial tail. I suspect it's there for the poor man's slipper clutch, i.e. jack the idle revs to about 3000...
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Isn't that what the fast idle lever is for? Apparently you can set it up to be basically cruise control on the TLS
 
TwistedKestrel said:
Isn't that what the fast idle lever is for? Apparently you can set it up to be basically cruise control on the TLS
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There's actually also a choke on the RC, though I'm not sure if it's a choke or fast idle. Only bumps rpm by about 300, so not much good for cruise or for avoiding locking the rear in hard braking...
 
I guess I can't say with 100% certainly that it's just fast idle, but all the PGM-FI bikes I know of that vintage will have a fast idle, except the Blackbird which has a mechanical automatic fast idle (wax motor). For some reason Honda put the fast idle knob directly on the throttle body on my 919. I guess for the same reason that they used steel instead of aluminum on the brake rotor carriers... which they did also make for the CBR600F4i, a part that is dimensionally identical. I'm sure it saved them millions
 
TwistedKestrel said:
I guess I can't say with 100% certainly that it's just fast idle, but all the PGM-FI bikes I know of that vintage will have a fast idle, except the Blackbird which has a mechanical automatic fast idle (wax motor). For some reason Honda put the fast idle knob directly on the throttle body on my 919. I guess for the same reason that they used steel instead of aluminum on the brake rotor carriers... which they did also make for the CBR600F4i, a part that is dimensionally identical. I'm sure it saved them millions
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Honda calls it a choke in the manual, for what that's worth, and it's actually a pull knob located on the left side of the bike just at the back of the upper fairing. I've never thought to look at what it actually does to the throttle bodies. The idle adjuster knob is in a similar spot on the right side, and it essentially moves the stop for the throttle cable. Neither is accessible when you're on the bike...
 
My RC needed the choke pulled out almost every start?
If you leave it on for any length of time, the motor will run like a bag of dirt.

Most bikes are now fuel injected. The computer will be able to adjust for any elevation or air density issues.
Idle is set at the factory. Most riders will have absolutely no reason to adjust idle speed.
They make it hard on purpose, so you don't mess things up.
 
Low rider said:
My RC needed the choke pulled out almost every start?
If you leave it on for any length of time, the motor will run like a bag of dirt.
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Yep, same for mine. Only needed for cold start, leave out for a couple of seconds, then push in as the revs stabilise, maybe 10 or 15 seconds. Have never tried to run it open, but if it runs rough, that suggests an actual choke rather than a fast idle. Early FI, still runs like a carb'ed bike in a lot of ways.
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