bmw r75/5 idle

[lelocp]

my bike idles at 1400 and i cant lower it because the idle adjustment screw is all the way out(not touching the lever). I did the valve lash but i never checked the timing. Could this have an effect on the idle speed? could it also be the advance?

[Crunch]

It's possible that the advance is sticking. The springs do get weak with age. My R90 has a similar problem before I replaced the springs and cleaned and lubed the advance mechanism. Have you also checked the pilot jet screw settings? But just do one thing at a time.

[lelocp]

how do you do the pilot screw setting

[ME 109]

If the idle adjust screws are not touching the throttle 'arm?' it may be that your butterfly plate/s are not shutting off completely.
'Course it could also be that the throttle cables might be holding the throttle open. Is there slack at the carbies when the throttle is backed all the way off?

[Crunch]

Here is a link to the Bing carburetor manual. A very good reference if you are going to maintain an airhead.
http://www.bingcarburetor.com/manual.html

ME109 makes a very good point about the throttle cables. There are many possible reasons for a high idle and checking off each possibility one at a time will get you where you want the bike to be.

[lelocp]

there is slack at the throttle cables. So if i have slack at the cables and there not holding up the butterfly then i would suspect the butterflys to be closed if the throttle adjuster screw is all the way out. I was thinking... could my approach to adjusting and syncing the carbs cause this to happen or would a faulty mechanical weight cause idle adjustment issues?

[ME 109]

Push down on the the 'levers' when idling and see if there is a difference.
An air leak could cause lean idle and hihg rpm. check carb to inlet spigot rubbers for condition and tight clamps.
Worn butterfly o ring is another potential air leak causing lean running.

I don't know a thing about the advances, never been in there.

Pull the carbs and hold up to the light and see if the butterflys are completely sealing. Lift the slide up out of the way and look through the carb. With the idle adjusters backed right off, there should be no light visible around the edges of the butterfly plate. Even a little light will allow a higher idle.

[ME 109]

Check the timing, it will alter idle.
I'm not sure what rpm incorrect timing could achieve with the idle screws backed off...

[lelocp]

i checked the butterfly and noticed that there was light around the edges, now what could cause this, are the butterflies worn? Also how do you known if you have 40mm carbs or 32 mm. I noticed that these carbs say 32mm on the intake side of the carb, the carb number is 64/32/328, are these the wrong size carbs for the bike?

[ME 109]

Not sure what carby is correct for your bike but I doubt it would be 40mm.

A butterfly plate may be worn, or it may be that it has moved in the shaft. The screws may have loosened or the carbs may have been serviced and the butterflys left incorrectly positioned.
Got to be careful when adjusting the butterfly to ensure the screws cannot come out later on. Some here recommend loctite, not sure which one.
The butterfly plate has to be put in the correct way also. Upside down doesn't matter, but back to front does.
The top and bottom edges of the butterfly plate are champfered to assist in sealing.

With the butterfly screws backed off, manipulate the shaft and plate so that the plate will assume the correct position when the butterfly shaft is in the fully closed position. Difficult to explain but you will understand when you do it.
It may be possible that the carby throat is worn where the butterfly plate contacts...........not sure about this tho'