I did the tappets a few months back. Haven't ridden it since late September after I replaced the broken starter motor. I thought I should rectify that.
Charged the battery then got it running. It was rough...
1. The Bosch W6DC was kaput. No spark. Easy fix. I managed a 20 minute warmup ride, took a couple of tools and it was better by the time I got home.
2. No change to rpm when looking for highest idle tweaking the R mixture screw.
I had a couple of spares with better orings. Installed. Easy fix.
3. Got it idling much better...except now it's wandering from 1100 to 2800rpm.
Getting late so stopped. I guess I have a leak somewhere. Tomorrows task to sort that...
I suspect the cables might need replacing too.
Wandering.......indicates a air leak somewhere? To narrow the leak down, I used to use a quick carb cleaner spray to the carb area and listen for idle changes.
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04 R1150RT ~ 78 R100/7 ~ 84 RS ~ 93 K1100RS ~ 65 R60/2
Randy in Round Rock
dwerbil wrote: ↑Wed Jan 29, 2025 9:57 pm
Wandering.......indicates a air leak somewhere? To narrow the leak down, I used to use a quick carb cleaner spray to the carb area and listen for idle changes.
Yep, same thoughts. I went over all the intake tube connections and tweaked them a little more. Some "start ya bastard" sprayed about afterwards didn't show an increase in rpm, more stable.
However, no time today to ride it to correct warmup. Hopefully tomorrow. The heat is on it's way here...~40C early next week so tomorrow will need to be the day.
With airheads you need to set the idle mixture and idle speed with the engine fully warmed through... that's 'ten mile' ride warmed through not 'two minutes in the garage with the engine idling' warmed through. If you don't, the idle will invariably be way too high when the engine is up to temperature.
Not insisting this is your problem but I've known owners search high and low for air leaks, exhaust leaks, sticking advance mechanisms... you name it, only to find that five minutes fettling with a screwdriver and a hot engine cures the issue.
Yes, thanks Rob. In the first instance yesterday, it had been well warmed up with a 20 minute ride. The wandering idle was then.
The second instance today it was inadequately warmed up (deliberately...didn't have a lot of time) but a little pre startup tightening/fettling seems to have removed the wandering. I'd had the airbox off last year replacing these...
...and the hose clamps did allow more tightening.
The third instance should be tomorrow, a good warm up and see what it's doing. Hopefully get it sorted before it gets too hot to ride it!
I'm still expecting a high idle, but hoping it doesn't wander.
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Success. A decent 30minute warm up ride in 27C temp resulted in a high idle at 2500rpm but without any wandering. A good start A bit of fettling with the idle adjuster and all good at 1100rpm.
I spent a little time just feeling the tension on the throttle cables and adjusting them to something that felt equal enough with a visually equal lift time. Once running it seemed the cable adjusters were very close but still took a little bit of back and forth between sides. It now sounds good and pulls smoothly to 4000rpm. The test ride was satisfying.
I'm using a harmoniser to confirm what I'm hearing and feeling, trying to adjust with the harmoniser screen out of sight. I don't do it frequently enough to make tuning the Bings an intuitive skill. Still, I'm better at it than I was 10 years ago.
AI overview via Google wrote:To tune a 40mm Bing carburetor, primarily focus on adjusting the idle mixture screw and throttle linkage to achieve the correct idle speed, then fine-tune by changing the main jet if necessary, while ensuring proper float level and checking for any blockages in the jets or passages; always consult your specific motorcycle manual for precise settings and procedures.
Key steps:
Basic Checks:
Clean the carburetor thoroughly: Remove the carburetor and disassemble it to clean all parts, including jets, float chamber, and passages, with carburetor cleaner.
Inspect float level: Ensure the float level is within the specified range.
Check for wear: Examine the needle valve and seat for wear and replace if necessary.
Idle Adjustment:
Set throttle linkage: Ensure both throttle butterflies open equally by adjusting the linkage screws.
Idle mixture screw:
Turn the idle mixture screw fully clockwise (leanest setting), then back it out 1.25 turns counterclockwise.
Start the engine and adjust the idle mixture screw slightly clockwise or counterclockwise until the engine runs smoothly at the desired idle speed.
Main Jet Adjustment (if needed):
Identify the main jet size: Check your motorcycle manual to determine the recommended main jet size for your riding conditions.
Replace the main jet: If the engine is running too lean (high RPM, poor acceleration), try a slightly larger main jet; if too rich (sluggish acceleration, black smoke), try a smaller main jet.
Important points to consider:
Sync the carburetors (if dual):
If your motorcycle has two Bing carburetors, ensure they are synchronized to provide equal air intake.
Listen for engine sounds:
Pay attention to engine sounds while adjusting the mixture, as a smooth idle and consistent power delivery indicate proper tuning.
Ride and fine-tune:
After initial adjustments, take your motorcycle for a test ride and fine-tune further based on your riding experience.
Tuning 40mm BING CV carburetors for BMW motorcycles by ear.
15 Dec 2008 — On both carbs, if they're mounted, you can use a thin piece of paper between the throttle adjuster screw and where the ...
Wrench'n Ride'n
HOW & WHY OF TUNING BING CARBURETORS
Use the carburetor piston Adjusting Screw to adjust the idle RPM. Turn this screw in a counterclockwise direction until the Carbur...
advancedpowerplant.com
Adjusting the Carburettor | Vanguard Engines
If your carburettor has a main jet adjustment screw at the base of the float bowl, turn the screw clockwise until you feel it just...
Vanguard® Power
I spent a little time just feeling the tension on the throttle cables and adjusting them to something that felt equal enough with a visually equal lift time. Once running it seemed the cable adjusters were very close but still took a little bit of back and forth between sides.
I use the knitting needle method for a basic mechanical balance. Take two slim and very lightweight knitting needles and pierce a short length of rubber tube that pushes onto the inside of the butterfly spindle. Then sit astride the bike and gently open the throttle while watching both needles to see which twitches first. Amplifying the movement of the spindle by that long length makes It very sensitive.
I managed a 20 minute warmup ride, took a couple of tools and it was better by the time I got home. 
early next week so tomorrow will need to be the day.
Success. A decent 30minute warm up ride in 27C temp resulted in a high idle at 2500rpm but without any wandering. A good start 