She's a 1985 K100RT, and when stopped for a light, she surges -- just a little. The tach needle hardly moves when I'm stopped, just sort of vibrates a bit around 750. But the engine goes up and down and sounds a bit like it's saying Wow...Wow...Wow...Wow. Doesn't really bother me, but I am curious as to what might cause this.

I have exactly the same problem on a 1988 model and am in the process of stripping the fuel injection and various rubber connections in the hope of finding air leaks. I made a start and will hopefully have it in bits Friday. Its 26 years old and looks like its never been apart and is testimony to the reliability of these engines (92,000 miles) Various posts on this excellent Forum indicate this is probably the culprit. John

Air leaks is likely cause, 750 sounds low rpm for idle, rev her up a bit may smooth her out.

Thanks, gents. I'll check her for leaks. When I use the throttle to raise the idle speed, she definitely does smooth right out. I'll try setting the speed a tad higher later today and see what happens.

John

Idle should be 950 (+/- 50) on these bikes.

Stamford wrote:She's a 1985 K100RT, and when stopped for a light, she surges -- just a little. The tach needle hardly moves when I'm stopped, just sort of vibrates a bit around 750. But the engine goes up and down and sounds a bit like it's saying Wow...Wow...Wow...Wow. Doesn't really bother me, but I am curious as to what might cause this.

Idle speed should be 950 RPM, + or - 50 RPM. 750 RPM is too low.

Good write up here on checking and replacing inlet rubbers etc.

http://www.motobrick.com/index.php?topic=624.0

good luck !

not hard to do ...but it is difficult to reinstall the throttle bodies and plenum onto old and hardened rubbers, the first time .

just takes time and patience ....to get the right technique and result .

Dicke wrote:Good write up here on checking and replacing inlet rubbers etc.

http://www.motobrick.com/index.php?topic=624.0

That removal and install part of the process is targeted at the K1100's which don't have a bloody big air plenum above the TBs.

The technique to the K100 is to remove the air filter box and MAS assembly completely from the right side of the motor and let them gently dangle from the MAS harness connection.  Support the MAS if possible to ease strain on the cabling.  This now offers space behind the plenum.  Move the cable harness away from the top of the plenum if at all possible to give headroom.  It helps to remove the TPS connection and the vacuum connection from TB4.

Then, loosen the rubber bushing clamps from the TB side (this may involve cutting the lower four Oetiker clamps instead) and carefully wiggle the plenum upwards and backwards away from the TB throats and inwards towards the space previously occupied by the air filter box.  Easy does it.  The rubber bushings should pop off the TBs remaining attached to the air plenum.  Once they are all clear, you can extract the air plenum out either side of the bike.

Installation is the opposite of removal.  Since you'll probably be using adjustable clamps on the install, make sure to orient them (1) for easy access to the screws and (2) to prevent interference with the throttle's moving parts.

Great advise from Rob. One of the clamps to pay real attention to is the rear-most unit, as that clamp needs to be at an angle, otherwise it interferes with the cam movement of the 'choke'. Not difficult, but easy does it!

I'm also in the midst of this job on my bike and this writeup was recommended to me. http://classickbikes.com/ckb.tech/0.ckb.tech.files/intakeman/intakeman.htm

Now I'm just waiting on parts. Ordered intake parts from BikeBandit.com and they are taking forever. I've recently ordered som parts from Bob's BMW in Maryland. They don't have a great selection online but over the phone, they seemed pretty knowledgeable on our dear ol K's.

For syncing the throttle bodies, do you guys make your own synchronizer or use a particular brand?

Much thanks for all the good advice and instructions. Yes, she is definitely happier and more stable around 950 rpm. The leak check is still a good idea, but will have to wait until I can get the time to pull everything apart. In the meantime, she is still a joy to ride and keeps me smiling.

John